PCC Jan/Feb 2019

January/February 2019 

Clonal Paradox Rootstocks Hold Their 

own in Tehama County Howard Trial 

A Nitrogen Fertilization Tool for Drip 

Irrigated Processing Tomatoes 

2018 Armyworm Season in Rice 

California Citrus Network: 

An Online Forum to Facilitate Communication and 

Information Exchange Regarding California Citrus 

JANUARY/FEBRUARY 2019 

VINEYARD 

REVIEW 

pages 21-42 

PUBLICATION 

Volume 4 : Issue 1 


www.progressivecrop.com 

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4 

IN THIS ISSUE 

Clonal Paradox 

Rootstocks Hold their 

own in Tehama County 

Howard Trial 

PUBLISHER: Jason Scott 

Email: jason@jcsmarketinginc.com 

EDITOR: Kathy Coatney 

ASSOCIATE EDITOR: Cecilia Parsons 

Email: article@jcsmarketinginc.com 

PRODUCTION: design@jcsmarketinginc.com 

Phone: 559.352.4456 

Fax: 559.472.3113 

Web: www.progressivecrop.com 

10 

16 

22 

28 

34 

38 

44 

A Nitrogen Fertilization 

Tool for Drip Irrigated 

Processing Tomatoes 

2018 Armyworm Season 

in Rice 

VINEYARD REVIEW 

Habitat Diversification 

for Pest Management 

in Vineyards—More 

Complicated Than It Seems 

Improving Grape Coloration 

and Ripening Using the 

Plant Hormone Ethylene 

The Impacts of Smoke to 

Vineyards 

Field Evaluation of Seven 

Rootstocks Under Saline 

Condition 


An Online Forum to 

Facilitate Communication 

and Information Exchange 

Regarding California Citrus 

10 

16 

VINEYARD 

REVIEW 

21 

CONTRIBUTING WRITERS & 

INDUSTRY SUPPORT 

Dr. Greg W. Douhan 

University of California 

Cooperative Extension, 

UCCE Citrus Advisor, 

Tulare, CA 

Luis Espino 

Rice Farming Systems 

Advisor, University of 

California Cooperative 

Extension 

Daniel Geisseler 

Associate UCCE Specialist, 

UC Davis and Kelley Liang, 

Junior Specialist UC Davis 

County 

Glenn McGourty 

Winegrower and Plant 

Science Advisor, UCCE 

Mendocino and Lake 

counties 

Luke Milliron 

UCCE Farm Advisor 

(Butte, Tehama, and Glenn 

Kevin Day 

County Director and 

UCCE Pomology Farm 

Advisor, Tulare/Kings County 

Dr. Brent Holtz 

County Director and UCCE 

Pomology Farm Advisor, San 

Joaquin County 

Steven T. Koike, 

Director, TriCal Diagnostics 

Counties), Richard 

Buchner, UCCE Farm 

Advisor Emeritus and 

Allan Fulton UCCE 

Irrigation and Water 

Resources Advisor 

Tehama, Colusa, Glenn, 

and Shasta Counties 

Houston Wilson 

Asst. Cooperative 

Extension Specialist 

Kearney Agricultural 

Research and Extension 

Center Dept. 

Entomology, UC Riverside 

George Zhuang 

and Matthew Fidelibus 

University of California 

Cooperative Extension, 

Fresno County, 

Department of Viticulture 

and Enology, University of 

California (UC) Davis 

UC COOPERATIVE EXTENSION 

ADVISORY BOARD 

Emily J. Symmes 

UCCE IPM Advisor, 

Sacramento Valley 

Kris Tollerup 

UCCE Integrated Pest 

Management Advisor, 

Parlier, CA 

The articles, research, industry updates, company profiles, and 

advertisements in this publication are the professional opinions 

of writers and advertisers. Progressive Crop Consultant does 

not assume any responsibility for the opinions given in the 

publication. 



3

sites. Second, because they are clonally 

propagated, they will impart less genetic 

variability and be more predictable in 

the orchard. Disadvantages include 

the loss of genetic diversity in orchard 

plantings and that additional expertise 

is required to micropropagate, 

nursery culture and graft to produce a 

commercially viable product. 

Clonal Paradox 

Rootstocks Hold their 

own in Tehama County 

Howard Trial 

By: Luke Milliron UCCE Farm Advisor (Butte, Tehama, and Glenn 

Counties), Richard Buchner, UCCE Farm Advisor Emeritus and 

Allan Fulton UCCE Irrigation and Water Resources Advisor Tehama, 

Colusa, Glenn, and Shasta Counties 

All photos courtesy of Luke Milliron 

Land available for perennial orchard crops is limited in the Central Valley, which 

often results in farmers either planting on less productive and more challenging 

soils or removing existing non-productive orchards and replanting them. 

Non-traditional orchard soils present challenges because they may have poorer 

nutrient availability or water quality. Replanting after an existing orchard puts a 

farmer at risk of a replant problem, when soil pathogens and nematodes from the 

first orchard inhibit performance of the replant orchard. 

One solution for managing replant problems is to replant with a different species 

(e.g. walnuts to almonds). Another possibility is to develop rootstock genetics to 

manage the replant problem. The California walnut industry traditionally utilizes 

two rootstocks for commercial production. Northern California Black (Juglans 

hindsii) or Paradox hybrid seedling (Juglans hindsii x Juglans regia). Both rootstocks 

are open pollinated resulting in genetic variability. Due to superior vigor, better 

adaptability to marginal soils and lower susceptibility to Phytophthora and crown 

and root rots, Paradox is the preferred rootstock for Northern California. Recent 

technology has resulted in micropropagation and commercial availability of three 

new clonal Paradox walnut rootstocks, VX211, RX1, and Vlach. These rootstocks 

are clones of seedling Paradox judged by researchers and breeders to offer superior 

traits. 

Clonal rootstocks may have several horticultural advantages. First, they can be 

selected for desirable attributes such as disease resistance, nematode tolerance, and 

vigor, giving farmers the opportunity to match rootstock selection with planting 

University of California (UC) 

and United States Department of 

Agriculture (USDA) researchers have 

been trialing the three new clonal 

Paradox rootstocks in experiments 

across the California walnut growing 

region. Work in controlled greenhouse 

studies, as well as field trials have shown 

that the clonal Paradox rootstock 

VX211 offers lesion nematode tolerance, 

and that RX1 offers moderate resistance 

to Phytophthora crown and root rot. 

Their research has also suggested that 

all three commercially available clonal 

Paradox rootstocks (VX211, RX1, and 

Vlach) generally have lower incidence 

of crown gall compared to the standard 

seedling Paradox. RX1 generally has the 

lowest crown gall incidence and may 

have low to moderate resistance. 

Recent History of Clonally 

Propagated Paradox 

Clonally propagated Paradox rootstocks 

have been available since 1999 with the 

release of Vlach, which originated from 

a vigorous Paradox tree in Stanislaus 

County. In 2007 RX1 and VX211 were 

released by the University of California 

and USDA, after being vetted for 

several years. The three clonal Paradox 

rootstocks are sold as potted rootstock, 

or they are June-budded or grafted 

to the walnut variety of choice at the 

nursery and sold as bare root trees. The 

three rootstocks are now planted across 

thousands of acres in California. 

For more information on the 

terminology, propagation, availability 

and pest interactions of walnut 

trees in the nursey trade, please see: 

sacvalleyorchards.com/walnuts/ 

orchard-development/walnut-trees-inthe-nursery-trade/ 

Tehama County ‘Howard’ Clonal 

Rootstock Trial 

One of the trials underway to evaluate 

the commercially available clonal 

Paradox rootstocks is located in a 

Continued on Page 6 

4 Progressive Crop Consultant January/February 2019

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5

Continued from Page 4 

Howard orchard in Los Molinos, 

California (Tehama County). The 

objective of this plot is to evaluate and 

compare the clonal rootstocks RX1, 

VX211 and Vlach to seedling Paradox 

and nursery budded June-bud Vlach 

trees. To evaluate these rootstock 

treatments against each other we 

measured trunk cross sectional area 

(TCSA), dry in shell yield, edible yield, 

percent jumbo walnuts, percent light 

kernels and percent mold. 

The clonal rootstock experiment in 

Tehama County was planted in March 

of 2009 as part of a large commercial 

Howard walnut orchard planted in a 

north/south orientation, at a 14-foot 

by 26-foot hedgerow configuration. 

The Tehama Soil Survey lists the soil as 

class one Columbia loam. The previous 

planting was Hartley walnut and the 

site was pre-plant fumigated with 400 

pounds of methyl bromide per-acre. 

The rootstock treatments were planted 

as three adjacent rows of six trees and 

replicated in five randomized plots. 

Trees are micro sprinkler irrigated and 

managed as part of the larger orchard. 

Planting and Establishment 

RX1, VX211 and Vlach were 

micropropagated by North American 

Plant Lab, Lafayette Oregon and grown 

for one year in a conventional walnut 

nursery, machine harvested and planted 

as soon as possible following digging. 

Seedling Paradox from the same 

nursery was planted as a control or 

reference rootstock to compare to the 

clonal Paradox treatments. June-budded 

Vlach, nursery grafted to Howard 

was included as the grower standard, 

since it is the rootstock and nursery 

product utilized in the orchard outside 

the plot. RX1, VX211, Vlach and the 

seedling Paradox were planted in March 

2009 as ungrafted trees and patch 

budded to Howard in September 2009. 

Unfortunately, freezing temperatures in 

December of 2009 resulted in very poor 

bud take. 

To ensure that all trees were treated 

equally, RX1, VX211, Vlach and the 

seedling Paradox were all re-grafted 

in May 2010 using whip grafts. Not all 

of the 2010 whip grafts took and the 

remaining trees were again whip grafted 

in May of 2011. Finally, all May 2011 

grafts were successful, and all trees 

had Howard scions in 2011. Note that 

the June-budded Vlach, propagated 

by the Bonilla nursey, were already 

grafted to Howard when planted in 

March 2009. Consequently, those trees 

have an advantage of over two years of 

uninterrupted growth compared to the 

other rootstocks, which is reflected in 

growth and yield measurements. 

Tracking Growth and Yield 

In each three adjacent row plot the 

center six trees are the measured trees 

with six guard trees to the east and six 

guard trees to the west. Tree and crop 

measurements include trunk cross 

sectional area, calculated using trunk 

circumference 12 inches above the graft 

union. Dry in-shell yield is calculated 

using the total field green weight 


(measured by load cell at harvest) 

multiplied by a green field weight 

to dry in-shell weight conversion, 

calculated from subsamples. 

Subsamples were also used to 

commercially evaluate nut quality. Due 

to tree mortality, not every plot had the 

original six trees, consequently total 

plot weight is divided by the number of 

harvested trees per plot and reported 

as weight per tree. Edible yield, percent 

jumbo walnuts, percent light kernels 

and percent mold were taken directly 

from the commercial grade sheets. 

Biological Controls for 

Anthracnose, Alternaria, N.O . W., 

and more... 

Field grafting was a tremendous 

challenge in this experiment, and 

points to the benefit of selecting 

nursery grafted trees if available. For 

this experiment, nursery grafted trees 

on clonal rootstocks were not available 

and field grafting was the only option. 

The key consequence of the grafting 

challenges were graft age differences 

throughout the plot. Assuming graft 

differences would decrease with 

time as trees matured, full plot yield 

measurements were delayed until 2017 

to minimize to the greatest extent 

possible any graft date differences. 

Recall the June-budded Vlach were 

planted already nursery grafted so 

they had an age advantage which is 

probably responsible for their superior 

performance through 2018. Again, 

tree age may minimize or reduce that 

effect, so additional years of yield 

measurement may show a decline 

in the competitive growth and yield 

advantage of June-budded Vlach. 

Resulting Growth 

The key comparisons are the 

micropropagated RX1, VX211, Vlach 

and the industry standard seedling 

Paradox. Interestingly, 2016 TCSA 


marronebio.com 



7

Table 1. 2017 Tehama County Clonal Paradox Rootstock Comparisons 

Rootstock 

2016 

TCSA 

cm 2 

Dry In shell 

Yield lbs/tree 

% 

Edible 

Yield 

% 

Jumbo 

% Light 

Kernel % Mold 

RX1 233 a 52.96 a 48.49 a 64.4 a 76.0 a 9.0 b 

Paradox seedling 234 a 59.20 ab 48.87 ab 65.6 a 79.8 ab 8.0 b 

VX211 235 a 63.90 ab 51.11 ab 66.6 a 84.0 bc 4.6 ab 

Vlach 253 a 68.60 b 50.80 ab 71.0 a 84.8 bc 5.6 ab 

June-budded Vlach 315 b 69.50 b 51.60 b 70.2 a 86.0 c 3.0 a 

Table 2. 2018 Tehama County Clonal Paradox Rootstock Comparisons 

Rootstock 

Dry In shell 

Yield lbs/tree 

% 

Edible 

Yield 

% 

Jumbo 

% Light 

Kernel % Mold 

RX1 38.86 a 43.66 a 73.4 a 76.4 a 5.2 a 

Paradox seedling 42.77 ab 43.08 a 66.8 a 80.2 a 3.4 a 

VX211 43.52 ab 43.74 a 66.0 a 79.2 a 3.0 a 

Vlach 46.75 ab 43.71 a 70.8 a 82.6 a 3.0 a 

June-budded Vlach 52.42 b 44.68 a 64.4 a 83.2 a 3.2 a 

Table 1 & 2 . Treatment means for tree size (trunk cross section area, TCSA cm2), dry in shell yield (lbs/tree) and quality 

comparisos for clonal Paradox rootstocks in Tehama County. If the rootstock treatments do not share a common letter in 

the column to the right of the averages, they are statistically different from one-another. 


measurements were not significantly 

different (Table 1) for those four 

rootstocks. Notice that only Junebudded 

Vlach trees were statistically 

significantly greater for TCSA in 2016. 

2017 and 2018 Harvest Findings 

In 2017 dry in-shell yield generally 

favored June-budded Vlach and Vlach, 

with RX1 imparting statistically lower 

yields and VX211 and Paradox seedling 

falling in-between (Table 1) statistical 

differences are signified by not sharing 

a common letter). The following year 

yields were significantly lower overall, 

and the June-budded Vlach again 

imparted statistically higher yield than 

the RX1, with the other rootstock 

treatments falling in-between (Table 2). 

Through these two harvests, the Junebudded 

Vlach trees with the growth 

advantage from not being field grafted, 

have been amongst the most productive 

trees in the plot. The trunk crosssectional 

area, or TCSA of June-budded 

Vlach was greater than the other 

rootstocks in 2016. Trees with larger 

trunks and presumably conferring 

larger canopies would be expected to 

produce more crop. 

The nut samples gathered for Junebudded 

Vlach were wetter (i.e. greater 

percent of moisture loss during drying) 

than RX1 or Paradox seedling in 2017 

and wetter than all other rootstock 

treatments in 2018. Wetter Junebudded 

Vlach might indicate they were 

harvested a little early being larger 

more robust trees, again due to their 

advantageous early start. 

Edible yield measurements favored 

June-budded Vlach, compared to RX1 

in 2017, with the other rootstocks 

falling in-between. In 2018 edible yields 

were lower overall and not significantly 

different across rootstocks. Nut size 

characterized as percent jumbo walnuts 

did not statistically differ between the 

five rootstocks in either year. Looking 

at the kernel quality attributes (percent 

light kernels and percent mold), values 

favored June-budded Vlach, Vlach, 

and VX211 in 2017. RX1 and seedling 

Paradox seedling tended to impart 

fewer light kernels in 2017. They also 

had more kernel mold compared to 

June-budded Vlach in 2017. More 

refined canopy measurements might 

confirm the possibility that RX1 and 

seedling Paradox trees featured a 

more open canopy with walnuts more 

vulnerable to heat/sun damage from 

the unusually hot 2017 growing season 

in Tehama County. There were no light 

kernel and mold differences between 

rootstocks in 2018. Despite the lack of 

statistical differences in 2018, RX1 again 

had numerically fewer light kernels 


and higher percent mold. Percent mold 

was lower in 2018, possibly due to the 

smoky summer in the Sacramento 

Valley that provided some protection 

from sunburn related mold, compared 

to the previous summer of recordbreaking 

temperatures. 

Nursery Product and the 

Importance of a Good Early 

Start 

This plot serves as an important lesson 

in the lingering ill effects of setbacks 

due to in-field grafting and budding 

problems. Vlach, already a vigorous 

rootstock was allowed to get a twoseason 

head-start on the rest of the 

field when planted as a June-bud. Many 

growers have had positive experiences 

with planting clonal rootstock and 

subsequently fall budding or spring 

grafting in the field with very high 

percentage take. However, unforeseen 

setbacks like the December frost in 

2009 that killed the new chip buds and 

the 50 percent take of the subsequent 

April’s bark grafts are also experienced 

by growers. As in the case of this trial, 

June-budded clonal rootstocks are not 

always available, and their higher price 

tag when they are available discourages 

some growers from planting them. 

At this orchard, the growth and yield 

advantage of the June-budded trees may 

fade in future years. However, for this 

site, the June-budded trees have been a 

solid investment. 

For more information on the various 

walnut nursery products available 

and how to handle them, please see: 

sacvalleyorchards.com/walnuts/ 

horticulture-walnuts/walnut-treetraining-different-nursery-products/ 

What Have We Learned 

About These Clonal Paradox 

Rootstocks? 

At the Howard orchard trial site in 

Tehama, the clonally propagated Vlach, 

VX211, and RX1 Paradox rootstocks 

have all performed competitively 

against the Paradox seedling rootstock 

that is standard in the region. The 

differences between the clonal 

rootstocks have been relatively subtle. 

The standard Paradox seedling has 

been in the middle of the pack across 

yield and quality attributes. Although 

not separating out statistically, VX211 

and Vlach have so far been numerically 

higher yielding and offered good quality 

(high percent light kernels and low 

percent mold). In a Solano county trial, 

cumulative yield from the 4th through 

8th leaf has also resulted in no yield 

differences between the three clonal 

rootstocks and Paradox seedling. At the 

Solano site Paradox seedling also falls 

numerically in the middle of the pack, 

with VX211 and Vlach in-front. UC 

and USDA researchers regard RX1 as 

moderately vigorous, Vlach as vigorous, 

and VX211 as highly vigorous. 

The class one Columbia loam and preplant 

fumigation with methyl bromide 

at the Tehama county trial site may 

mean that attributes like VX211’s 

tolerance of some nematodes and 

RX1’s moderate to high resistance to 

some Phytophthora species, have not 

had the opportunity to shine. Thus far, 

the nursery product choice of a Junebudded 

tree has been the big advantage 

at the site. At the site of your next 

walnut orchard, availability, cost, and 

the subsequent required handling of the 

various nursery products will all have 

to be judged. In addition, consider the 

attributes conferred by clonal rootstocks 

for vigor, crown gall, nematodes, and 

Phytophthora/wet feet when choosing a 

rootstock. Researchers will continue to 

test these rootstocks, as well as an even 

newer generation of clonally propagated 

rootstocks, across the California walnut 

growing region. 

For more information on selecting the 

right clonal rootstock for managing 

your soil and pest problems please 

see: sacvalleyorchards.com/blog/ 

walnuts-blog/selecting-the-right-clonalrootstock-for-managing-soil-and-pestproblems/ 

We want to sincerely thank an amazing 

team of UC and USDA researchers who 

have worked tirelessly on developing and 

testing new rootstocks for California 

walnut production. They include Janine 

Hasey, Chuck Leslie, Wesley Hackett, 

Pat J. Brown, Andreas Westphal, 

Michael McKenry, Greg Browne, Bruce 

Lampinen, Katherine Jarvis-Shean, Dani 

Lightle and Dan Kluepfel. This work is 

made possible by the funding support of 

the California Walnut Board. 

Comments about this article? We want 

to hear from you. Feel free to email us at 

article@jcsmarketinginc.com 

ORGANIC TREE WASH 

ELIMINATES FOOD SOURCES THAT CAN CAUSE: 

• Fire Blight 

• Gummosis 

• Canker 

• Bot Diseases 

ENHANCES FRUIT COLOR 

Use for, Tree Nuts, Stone 

Fruits, Apples, Pears, Citrus, 

Avocados, 

and Blueberries. 

ALSO HELPS TO CONTROL GROUND 

SQUIRRELS, GOPHERS, MICE, AND VOLES. 

Begin Spraying at bud break or 

2 to 4 inch shoot growth, two 

quarts per 100 GPA. 

Repeat every 14 days, mixes 

well with fertilizers, we 

recommend using, 

PURE PROTEIN DRY 15-1-1 



9

A Nitrogen 

Fertilization 

Tool for Drip 

Irrigated 

Processing 

Tomatoes 

By: Daniel Geisseler | Associate UCCE 

Specialist, UC Davis and 

Kelley Liang, Junior Specialist | 

UC Davis County 

The in the field trial four weeks before harvest. 

Photo courtesy of Daniel Geisseler. 

The processing tomato industry has 

seen a dramatic shift in production 

practices over the last 20 

years, caused mainly by a wide adoption 

of drip irrigation. While less than 10 percent 

of the acreage was drip irrigated in 

1999, this number reached 85 percent in 

2012. The shift from predominantly furrow 

irrigation to drip irrigation has contributed 

to strong yield increases. It has 

also changed fertilization management, 

with fertigation through the drip system 

now being common. Subsurface drip 

irrigation allows application of water and 

nitrogen (N) fertilizer close to the roots 

throughout the season to match crop requirements. 

Fertigation can increase the 

N use efficiency considerably, minimizing 

N losses to the environment. 

Applying the right amount at the right 

time requires knowledge about the N 

demand of the crop, the seasonal uptake 

pattern and the availability of other 

sources of N. Many factors that affect 

the balance between N availability and 

crop N demand are site specific, including 

yield potential, residual soil nitrate 

levels, nitrate in the irrigation water 

and N mineralized from organic matter 

during the growing season. This is 

especially true with residual soil nitrate 

levels at transplanting, which can vary 

considerably from one field to another 

and across years, as they depend on 

weather conditions, the previous crop 

and its management. 

Three years ago, we started a project 

with the goal to develop a user-friendly 

N fertilization tool for processing 

tomato producers and consultants. To 

achieve this goal, we first monitored N 

uptake in commercial fields. We then 

developed a template for a N budget, 

which takes into account crop N 

requirement, availability of non-fertilizer 

N and efficiency of N fertilizer 

use. Finally, we tested the budget in a 

replicated field trial. 

Nitrogen Uptake 

Plant samples were collected throughout 

the season at 3-week intervals in 11 

commercial fields located in Yolo, San 

Joaquin and Fresno counties. Plants 

were cut at the base and fruits picked 

and weighed. Fruits and vines were then 

dried separately and analyzed for total 

N content. 

The results from these fields revealed 

that little N was taken up during the 

first month after transplanting (Figure 

1, see page 12). On average, less than 

15 percent of the total aboveground N 



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11

300 

Esmated N uptake (lbs/acre) 

250 

200 

150 

100 

50 

0 

0 

20 

40 60 80 100 120 

Days aer transplanng 

Figure 1. Nitrogen accumulation in the vines and fruits of a processing tomato crop with an expected 

yield of 55 tons/ac. The curve is based on results from 11 commercial fields. 


was taken up during this period, which 

in most fields was less than 50 lb/ac. A 

moderate starter fertilizer application 

can therefore supply enough N during 

the initial 3-4 weeks after transplanting. 

The initial period of slow N uptake was 

followed by 8-10 weeks of rapid uptake, 

with daily uptake rates reaching 7 lb/ac 

in some fields. On average, more than 

80 percent of the total N in the aboveground 

biomass had been taken up 

by the time the plants reached the early 

red fruit stage. An adequate N supply 

is crucial during this period of high N 

demand, and N fertigation should be 

timed to avoid temporary N limitations. 

During the last month before harvest, 

N uptake was low and in some cases a 

decrease in the total biomass N was observed. 

After the crop reaches the early 

red fruit stage, N applications are generally 

no longer needed. Late applications 

may not be taken up by the plants, and 

will be at risk of being leached during 

the winter. 

Creating an N Budget Template 

Across all commercial fields, the tomato 

fruits contained 3 lb N/ton of fresh 

weight at harvest. The N in the fruits accounted 

for two thirds of the total N in 

the aboveground biomass. These values 

were used to determine total N requirement 

for the budget. As an example, the 

average N requirement of a 55-ton crop 

is 246 lb/ac. In most fields the plants 

were well supplied with N, and a value 

of 3 lb/ton for the fruits likely includes 

some luxury consumption. 

The N demand of a crop can be covered 

with fertilizer, residual soil mineral N, 

nitrate in the irrigation water and N 

mineralized from soil organic matter 

during the growing season. These 

sources need to be taken into account 

when determining the need for fertilizer 

N. With subsurface drip irrigation, the 

surface layer of the soil profile remains 

dry throughout the season, potentially 

restricting root activity and nutrient 

uptake. For the N budget, we assumed 

that only 50 percent of the pre-plant soil 

nitrate in the top foot can be accessed 

by roots. This assumption is a rough 

estimate which needs to be further 

investigated. This is especially important 

for the San Joaquin Valley where 

soil nitrate levels can be quite high and 

supply a significant portion of the N 

needed by the crop. For the residual soil 

nitrate in the second foot of the profile 

and for fertilizer N, we assumed that 80 

percent is taken up by the plants. 

Field Trial 

The budget calculations were validated 

in a replicated field trial at UC Davis 

in 2017 and 2018. The soil at the site 

was classified as a Yolo silt loam with 

a soil organic matter content of 1.8 

percent and a pH of 7.4. Tomatoes were 

transplanted onto 60-inch beds in early 

May both years. Twenty-five gal/ac of a 


Table 1. Nitrogen budget examples. Example 1 corresponds to the situation in the replicated field trial in 2018. Example 2 

assumes the same yield, but larger credits for residual soil nitrate and nitrate in the irrigation water. Credits were calculated 

based on the description in the text. 

Expected yield 

Expected N in fruits 3 lb/ton 

Expected N in vines 33 percent of total 

Expected N uptake 

Residual soil nitrate N 

Irrigaon water N 

Soil N mineralizaon 

Non-ferlizer credits 

st 

1 

nd 

2 

22 ac-in 

Difference (uptake - non ferlizer N) 

Starter applicaon 

In-season N(assumed efficiency:80 percent) 

58 

12 

11 

0 

Example 1 Example 2 

tons/ac 

ppm N 

ppm N 

ppm N 

lb N/ac 

174 

87 

24 

39 

261 

0 

40 

102 

159 

25 

167 

58 tons/ac 

25 

15 

10 

ppm N 

ppm N 

ppm N 

lb N/ac 

174 

87 

49 

53 

45 

40 

261 

187 

74 

25 

93 

liquid starter fertilizer (8-24-6, 0.5 percent 

Zn) was applied to all treatments. 

During the growing season, UAN 32 

was supplied via drip tape in 5 weekly 

applications starting one month after 

transplanting. Three application rates 

were compared in the trial. The intermediate 

or optimal rate corresponded 

to the amount calculated in the budget. 

This application rate was reduced or increased 

by 50 lb/ac for the low and high 

rate, respectively. All other management 

practices followed common practices 

for conventional processing tomatoes. 

The trial was machine harvested in late 

August both years. We expected a yield 

of 55 and 58 tons/ac in 2017 and 2018, 

respectively. 

Pre-transplant nitrate-N in the top and 

second foot of the soil profile ranged 

from 8 to 13 ppm (parts per million). 

Taking into account limited root access 

in the dry top soil, the available 

residual soil nitrate was about 50 lb/ac 

both years. The irrigation water did not 

contain any nitrate. Based on results 

from a different study which included 

the field trial site, N mineralization was 

assumed to be 40 lb/ac. Subtracting 

these N credits and the starter N application 

from the expected amount of N 

required, the N fertigation requirements 

were estimated to be 165-190 lb/ac in 

the two years of the study. The detailed 

budget for the second year is shown in 

Table 1. 

Average yields were higher than expected, 

reaching 58 tons/ac in 2017 and 63 

tons/ac in 2018 (Figure 2). 

Nitrogen application rate had no signif- 


80 

2017 

2018 

Yield (tons/ac) 

60 

40 

20 

0 

Low N Intermediate N High N Low N Intermediate N High N 

Figure 2. Yield in the replicated field trial. The N treatments had no statistically significant effect on yield. Each treatment 

was replicated five times. The tomatoes were machine harvested. Error bars indicate standard error. 



13


icant effect on yield. It may appear that 

the yield in the high treatment in 2018 

was greater than the other treatments. 

However, due to some pest issues, variability 

across the plots was quite high. 

Therefore, the statistical analysis concluded 

that it is likely that the observed 

difference is simply due to chance and 

not because of the higher N rate. 

Discussion of the Budget 

Approach 

Even though the measured yield exceeded 

the expected yield in both years, 

reducing the optimal N application 

rate by 50 lb/ac had no effect on yield. 

This was mainly due to the fact that the 

plants adjusted N uptake based on N 

availability. From the low N to the high 

N treatment, the N application rate was 

increased by 100 lb/ac, while the N in 

the aboveground biomass increased by 

87 lb/ac across both years. 

Our results suggest that using a value 

of 3 lb/ton may overestimate N requirements 

and that a fruit N concentration 

above 2.7 lb/ac is likely the result of 

luxury consumption. However, the N 

budget is based on marketable yield and 

not total yield. Therefore, the use of the 

higher value represents an adjustment 

for N in non-marketable fruits. 

While fertilizer N use efficiency decreased 

only slightly with increasing N 

application rate within the range of our 

study, the amount of N removed from 

the field with the harvested tomatoes 

only increased by 46 lb/ac when the N 

rate was increased by 100 lb/ac. Close 

to half of the increased N uptake was 

due to higher N contents in the vines, 

which were left in the field and later 

incorporated. The decomposition of the 

vines will release part of this N resulting 

in higher nitrate levels in the soil, 

increasing the risk of nitrate leaching 

with winter rains. While the increasing 

N uptake with increasing N application 

rates suggests that the optimal N rate 

can be considered a range rather than 

an exact number, it is still important to 

accurately estimate fertilizer N requirements 

in order to minimize the risk of 

nitrate leaching and to keep production 

costs low. 

Conclusions 

The results of this study were incorporated 

into a simple processing tomato 

N calculator, which is freely available 

online at http://geisseler.ucdavis.edu/ 

Tomato_N_Calculator.html. The 

calculator is easy to use and requires 

few readily available input variables. 

However, such a simple tool cannot 

capture all the factors that affect growth 

and yield of the crop in individual 

fields. Factors such as: differences in soil 

properties, crop management, disease 

pressure or weather conditions. While 

the assumptions used in the budget presented 

here provide a margin of safety 

for commercial producers, it is crucial 

to monitor the fields during the growing 

season in order to make adjustments 

if needed. Soil nitrate testing and leaf 

analyses are valuable tools to determine 

N availability and N status of the crop 

during the season. These tools allow for 

adjustments when the calculated N application 

rates do not match the plants’ 

demand. 

This project was a collaboration between 

the authors and Gene Miyao, 

UCCE Farm Advisor, Yolo, Solano & 

Sacramento counties; Brenna Aegerter, 

UCCE Farm Advisor San Joaquin 

County; and Tom Turini, UCCE Farm 

Advisor Fresno County. Funding was 

provided by the CDFA Fertilizer Research 

and Education Program (FREP). 




Photo courtesy of Daniel Geisseler. 


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2018 Armyworm 

Season in Rice 

By: Luis Espino | Rice Farming Systems Advisor, University of California Cooperative Extension 

Figure 1. This picture was taken in 2015 in a Glenn County field. The field had already been 

treated twice, but worms kept feeding on foliage. All photos courtesy of Luis Espino. 

For many years, armyworms have 

been considered a secondary pest 

in rice fields. Treatments were 

sometimes needed, but for the most 

part, most growers could get by without 

spraying an insecticide. That changed in 

2015, when a severe armyworm outbreak 

occurred throughout the Sacramento 

Valley. Infestations were worst in 

Butte, Glenn and Sutter counties. Severe 

defoliation was observed in some fields, 

where plants were eaten to the water 

level (Figure 1). That year, growers and 

pest control advisors realized that pyrethroids, 

a common insecticide group 

used on rice, do not do a good job controlling 

armyworms. The industry was 

able to obtain a Section 18 Emergency 

Registration for the insecticide Intrepid 

(methoxyfenozide), an insect growth 

regulator, but the registration came a bit 

too late, when the outbreak had passed. 

The next two years saw variable infestation 

levels, with 2016 being less problematic 

than 2017. Again, a Section 18 

registration was obtained for Intrepid at 

the end of June both years. 

In 2018, armyworm levels were variable, 

with high levels in some fields, and 

average levels in others. Intrepid was 

available from mid June until the end of 

the season. Severe defoliation as seen in 

2015 did not happen; however, this year 

growers and PCAs were on their toes, 

monitoring fields closely. 

Armyworm Cycle in Rice 

Two species of armyworms can be 

found in rice fields, the true armyworm 

(Mythimna unipuncta) and the western 

yellowstriped armyworm (Spodoptera 

praefica). In the past few years, the true 

armyworm has been the dominant 

species; however, there is evidence that 

in some years the western yellowstriped 

armyworm can be dominant. Adults of 

both species are nocturnal moths that 

most of us will not get to see during the 

day. These moths lay their egg masses 

in vegetation surrounding rice fields 

beginning in late May and through June. 

Their eggs are difficult to find 



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17

Figure 3. Armyworms usually pupate in the soil. In 

rice, however, they can find hiding place between 

tillers and pupate there. 


(I haven’t been able to find them in or near rice fields). The small larvae 

emerging from the eggs are very difficult to find also, hiding under clods and 

at the base of plants in levees and around rice fields. Their feeding is almost 

unnoticeable. As they grow, the larvae spread to other plants and their feeding 

increases. When they reach the fifth instar, larvae become voracious eaters that 

can defoliate plants quickly (Figure 2). In rice, this typically occurs in late June 

and early July. The last stage lasts six days, and during this time the larvae eat the 

most. Usually, growers and PCAs don’t notice the damage and worms in the field 

until they have reached the fifth instar. 

After the sixth instar the larvae pupate. In other crops, larvae drop to the soil, 

hide and pupate. In rice, larvae find hiding spots between tillers above the water 

and pupate there (Figure 3). Some 

of the pupae may drop to the water 

and drown, but some likely survive. 

Armyworm numbers climb up again 

during rice heading. There is so much 

foliage at this point that armyworm 

foliar feeding is not an issue. However, 

worms can feed on the panicles. 

Typically, larvae will chew on green 

panicle branches, causing blanking of 

the kernels on that branch (Figure 4, 

see page 20). In some cases, panicle 

injury can be severe. 

Monitoring 

One of the factors that make armyworm 

outbreaks a challenge to manage is 

that most of the time, defoliation is not 

noticeable until the worms are large. 

Large worms feed quickly, eat large 

amounts of foliage, and are difficult to 

control with any insecticide. 

Figure 2. Armyworms go through six instars during their development. The blue bars represent 

the duration, in days, of each instar. The red line represents how much foliage they can eat 

during each instar. For reference, 200 cm2 is equivalent to a third of a 8x11 inch paper sheet. 

Currently, the best guideline we have is 

to rely on percent defoliation or panicle 

injury. Once the defoliation reaches 

close to 25 percent of the foliage, a 

treatment is recommended. If 10 

percent of panicles show armyworm 

injury, a treatment is recommended. In 

order to time the treatments properly, 

growers and PCAs have to be “on top” 

of the field. I have heard many stories 

of fields that looked fine before the 

weekend or vacation, only to be found 

severely defoliated after only a few days. 


Pheromone Trapping 

I started monitoring the flight of 

armyworm moths in 2016 using 

pheromone traps. Monitoring moths 

does not predict if armyworms will be a 

problem in a particular field, but it lets 

us know when the peak of armyworm 

activity is happening, and therefore when 

we should expect armyworms in the field 

and step up the monitoring. Models that 

predict armyworm development based 

on temperature are available, and used 

together with moth flight monitoring, 

can help in estimating when larvae 

should reach the fifth instar in the field. 

In 2016, seven sites were monitored with 

pheromone traps. In 2017, 16 sites were 

monitored and the numbers e-mailed 

weekly to growers and PCAs. 

On average, the number of moths 

trapped per day at the peak of the early 

infestation was similar in 2017 and 

2018 (Figure 5, see page 20). However, 

the peak in 2017 was 10 days earlier 

than in 2018. It is possible that earlier 

infestations resulted in more injury 

because of defoliation of smaller plants. 

Additionally, 2017 was a late planted year 

because of late spring rains, meaning the 

crop was delayed. During heading, peak 

moth flight was much lower in 2017 than 

in 2018. In both years, panicle injury 

was not as common as foliage injury and 

rarely a problem. 

In general, traps in areas where a 

diversity of crops are grown had higher 

number of moths than areas where rice 

is the dominant crop. This is probably 

because armyworms are poliphagous, 

with other crops providing habitat and 

perhaps overwintering sites. Foliage 

treatments went out in locations where 

traps had peak catches of over 20 moths 

per trap per day; however, in some cases, 

higher catches did not result in worm 

populations that needed a treatment. 

Insecticides 

As mentioned before, pyrethroids do not 

do a good job controlling armyworms in 

rice. Grower and PCAs’ field experiences 

during the outbreak years confirm this. 

This year, field trials also confirmed 

these observations. Intrepid does a good 

job and affects worms quickly. Dimilin 

(diflubenzuron), another insect growth 

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19

Figure 5. Average 

number of moths 

trapped in 16 rice fields 

across the Sacramento 

Valley during 2018. This 

year, the first peak was 

similar to 2017, but it 

happened 10 days later. 

Even though a second 

peak was detected in mid 

August, injury to panicles 

was not widespread. 

Figure 4. Armyworm can feed on the rachis 

of panicle branches, causing blanking in 

those branches. 


regulator, also controls armyworm. 

However, the pre-harvest interval is 80 

days, allowing for its use only during 

the late June, early July infestation. Since 

this is the time when armyworms can 

be a critical problem, Dimilin can be a 

viable alternative. 

Conversations with growers and PCAs 

revealed an interesting trend. Since 

Intrepid was available early in 2018, 

before infestations started, growers and 

PCAs were more willing to scout their 

fields and wait to see if populations 

reached damaging levels. They knew 

that if they needed to treat, they could 

used Intrepid and achieve good control. 

Before 2018, a preventive approach was 

being tried by some, using insecticides 

before armyworms reached treatment 

levels, with the hope of catching 

them small and therefore improving 

control. In many cases, this resulted in 

more than one insecticide application 

targeting armyworms. 

Effect on Yield 

Research has shown that armyworms 

can reduce yield by defoliating rice 

or blanking kernels when feeding on 

panicles. A survey conducted early this 

year documented that average yield 

loses due to armyworm, after using 

an insecticide, ranged from 1.25 to 8 

percent. In 2015, growers sprayed on 

average two times to try to control 

armyworms. Treatments reported 

consisted mostly of pyrethroids and/ 

or carbaryl. Yield losses averaged from 

4 to 12 percent, but losses as high as 

24 percent were reported. In 2016 and 

2017 survey respondents reported 

higher yield losses due to armyworm 

infestations when they used pyrethroids 

than when using methoxyfenozide, 

indicating better armyworm control 

with methoxyfenozide. Yield losses 

from methoxyfenozide treated fields 

were 29 to 64 percent lower than from 

pyrethroid treated fields. 

Concluding Remarks 

It is impossible to predict how the 2019 

armyworm season will be. Hopefully, 

Intrepid will be available for use, but 

that is not a given. While Dimilin is a 

good option, remember the pre-harvest 

interval limitation. The armyworm 

trapping network will continue next 

year, so that growers and PCAs can 

increase their monitoring when moth 

populations start increasing and large 

larvae are predicted. The rice industry 

will continue to work to ensure control 

tools are available to growers and PCAs 

on a timely manner. 





JANUARY/FEBRUARY 2019 


In This Issue 

22 

Habitat Diversification for Pest 

Management in Vineyards—More 

Complicated Than It Seems 

28 

34 

38 

Improving Grape Coloration and 

Ripening Using the Plant 

Hormone Ethylene 

The Impacts of Smoke to 

Vineyards 

Field Evaluation of Seven 

Rootstocks Under 

Saline Condition 



21


Habitat Diversification for Pest 

Management in Vineyards— 

More Complicated Than It Seems 

By: Houston Wilson | Asst. Cooperative Extension Specialist 

Kearney Agricultural Research and Extension Center 

Dept. Entomology, UC Riverside 

Ammi majus blooming in a Sonoma County vineyard. 

All photos courtesy of Houston Wilson. 

Vineyard Habitat 

Diversification 

Cover crops, hedgerows and other ‌ 

on-farm habitat plantings can 

potentially attract and support 

beneficial insects that can then potentially 

increase biological control of 

pests—the key word here being potentially. 

The diversity and abundance 

of beneficial insects that can be found 

on a wide variety of non-crop plants, 

many of them flowering, has been very 

well documented over the past several 

decades. These data have subsequently 

been used to advocate for the establishment 

of on-farm habitat plantings, with 

the assumption that adding in non-crop 

plants that attract beneficials will (1) 

lead to more beneficial insects on your 

farm, (2) those beneficials will go on to 

attack the key pests that you’re concerned 

about and (3) they will do so in 

a manner that lowers pest populations 

below economic thresholds. 

This logic is embodied in a number of 

public and private programs as well 

as publications that promote on-farm 

habitat diversification. While this logic 

is not entirely off-base, the development 

of specific on-farm habitat strategies 

that can reliably and economically control 

arthropod pests in agriculture has 

remained fairly limited. This is primarily 

because such practices are very ecologically 

specific and must be tailored 

to the target pest and its key natural 

enemies, as well as the agronomic and 

economic requirements of the cropping 

system itself. As such, habitat diversification 

practices that work for a specific 

pest in a specific crop are not typically 

transferable to other crop-pest systems. 

Moreover, practices that may work for 

a given crop-pest system may not be 

readily transferable to the same croppest 

combination in another region or 

climate. This is not to say that on-farm 

habitat plantings have no potential, but 

rather that the development of practices 

that can produce consistent and 

economically relevant outcomes require 

research and development on a pest-bypest 

and crop-by-crop basis. 

Leafhoppers and Anagrus 

Parasitoids in California 

Vineyards 

Leafhopper pests in California vineyards 

include the Western grape leafhopper 

(Erythroneura elegantula), which 

is native to the state, along with two invasive 

species that arrived in the 1980s, 

the variegated leafhopper (E. variabilis) 

and Virginia creeper leafhopper (E. 

ziczac). These closely related leafhopper 

species all feed on grape leaves, which 

can reduce vine productivity, crop 

yield/quality, and the adults can be a 

nuisance at harvest. These leafhoppers 

are primarily controlled by a suite 

of parasitoids that attack their eggs, 

this includes Anagrus erythroneurae, 

A. daanei and A. tretiakovae. These 

Anagrus parasitoids are unique in 

that they seasonally move between 

vineyards and natural areas, such as 

riparian and oak woodland habitats. 

During the growing season, Anagrus 

parasitoids will regularly attack and 

reproduce on the eggs of Erythroneura 

leafhoppers in vineyards, but when 

vines senesce in the fall these leafhoppers 

enter a reproductive diapause and 

overwinter as adults in and around 

the vineyard, typically taking shelter 

in leaf litter or nearby vegetation. In 

the absence of Erythroneura eggs, the 

Anagrus parasitoids must seek out 

an alternate leafhopper species that 

continues to produce eggs over the 

winter, and these alternate hosts are 

typically located on plants outside of 

vineyards. When grape vines begin 

to develop again in the spring, the 

Erythroneura leafhoppers move onto 

the vines where they begin to feed and 

soon after start to lay eggs into the 

new leaf tissue. It is at this point that 



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23



the Anagrus parasitoids will leave their 

alternate hosts and then move back into 

the vineyard and resume attacking the 

new Erythroneura leafhopper eggs on 

grape leaves. 

Overwintering Habitat for 

Leafhopper Parasitoids 

Previous University of California (UC) 

research demonstrated that blackberry 

(Rubus spp.) and French prunes (Prunus 

domestica) were the primary plants that 

harbored the alternate insect hosts that 

the Anagrus utilized during the winter 

(Doutt and Nakata 1965, Kido et al. 

1984, Wilson et al. 1989). Follow-up 

studies demonstrated 

that Anagrus populations 

were higher and arrived 

earlier in vineyards that 

were closer to riparian 

areas where blackberry 

was abundant (Doutt 

et al. 1966, Doutt and 

Nakata 1973). Unfortunately, 

efforts to establish 

blackberry plantings in 

vineyards outside of riparian 

areas largely failed 

and any further desire to 

propagate this plant near 

vineyards was snuffed out 

when it was revealed that 

blackberry was a reservoir 

for Xyllela fastidiosa, the 

bacterium that causes 

Pierce’s Disease as well as a 

host plant for glassy-wing 

sharpshooters (Homalodisca 

vitripennis), which can transmit 

this pathogen to grape vines. That leaves 

us with the French prunes, which of 

course aren’t naturally occurring in the 

landscape like blackberry and thus provide 

a relatively limited overwintering 

resource for the Anagrus parasitoids. 

While some growers have attempted to 

establish French prunes in and around 

their vineyards, these overwintering 

refugia are dwarfed by the sheer quantity 

of vineyard acreage that needs to be 

colonized by these parasitoids. 

More recently, surveys conducted in the 

North Coast region identified a number 

of previously unknown overwintering 

host plants utilized by the Anagrus— 

most notably coyote brush (Baccharis 

pilularis) (Wilson et al. 2016). Not only 


is this plant abundant in the landscape, 

it’s drought tolerant, grows in very 

disturbed conditions, harbors Anagrus 

parasitoids year-round, and is a California 

native plant. Thus, in combination 

blackberry and coyote brush are likely 

responsible for supporting regional 

populations of these Anagrus parasitoids 

near vineyards. 

Summer Cover Crops 

Cover crops are incredibly useful for 

soil quality maintenance, as they can 

contribute to erosion control, improved 

water penetration, reduced compaction, 

and restoration of soil fertility—but can 

they also contribute to biological control 

of pests? In California, the use of 

Anagrus daanei parasitizes a leafhopper egg 

cover crops to attract beneficial insects 

to increase biological control of vineyard 

leafhoppers was first explored in 

the 1990s by various UC researchers. 

One series of trials evaluated fall-sown 

legume/grass cover crop blends that 

consisted of vetch (Vicia spp.), oats 

(Avena spp.) and/or barley (Hordeum 

sp.) in Central Valley vineyards (Daane 

and Costello 1998, Roltsch et al. 1998, 

Costello and Daane 2003, Hanna et al. 

2003). Rather than mow and plow these 

down in the spring, as is typical when 

they are used for soil management, the 

cover crops were left in place until they 

dried out in the early summer. In some 

cases, leafhopper densities were indeed 

reduced in the presence of the cover 

crop but this effect was actually due to 

changes in vine vigor—competition 

from the cover crop led to reduced petiole 

nitrate levels which had a negative 

impact on leafhoppers. Additional 

studies have demonstrated that leafhoppers 

prefer more vigorous vines as well 

as vines with greater levels of irrigation 

(Daane and Williams 2003). 

Another series of experiments explored 

the use of summer flowering cover 

crops in North Coast vineyards. One set 

of trials evaluated spring-sown species 

that required supplemental irrigation, 

this included buckwheat (Fagopyrum 

esculentum), sweet alyssum (Lobularia 

maritima), and sunflower (Helianthus 

annus) (Nicholls et al. 2000). Another 

set of trials used 

fall-sown species that 

relied on winter rains 

alone, these species 

were purple tansy 

(Phacelia tanacetifolia), 

bishop’s flower 

(Ammi majus) and 

wild carrot (Daucus 

carota) (Wilson et 

al. 2017). In both 

of these studies, the 

flowering cover crops 

attracted a lot of beneficial 

insects but this 

never translated to 

increased biological 

control of leafhoppers 

in the vine canopy 

itself. 

Finally, a study in 

the Lodi area assessed 

the influence 

of a perennial native grass cover crop 

that consisted of blue wildrye (Elymus 

glaucus), meadow barley (Hordeum 

brachyantherum) and California brome 

(Bromus carinatus) (Daane et al. 2018). 

Leafhopper populations were reduced 

in the presence of the cover crop but 

again the effect was due to changes in 

vine vigor—the cover crops reduced 

petiole nitrate levels which led to lower 

leafhopper densities. Furthermore, 

the deep-rooted perennial grasses also 

improved water infiltration which led 

to increased soil moisture and reduced 

vine water stress, which can also lead to 

lower leafhopper densities. 

Taken as a whole, these studies demonstrate 

that the effect of cover crops on 

Continued on Page 26

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Pending 

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CCA: 4.5 hour 

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8:00am 

8:30am 

9:00am 

9:30am 

10:00am 

10:45am 

11:00am 

11:30 

12:00pm 

1:00pm 

1:30pm 

2:00pm 

Laws and Regulations Update 

Marcie Skelton, Glenn County Agricultural Commissioner 

Mite Control in Almonds 

David Haviland, UCCE IPM Advisor, Kern County 

Walnut Husk Fly Management 

Dr. Bob VanSteenwyk, Entomology Specialist Emeritus, UC Berkeley 

Preventing and Managing Walnut Crown Gall 

Dr. Dan Kleupfel, Plant Pathologist, USDA ARS, Davis 

Break; Trade Show Open 

Butte-Yuba-Sutter Water Quality Coalition Update 

Rachel Castanon, Program Coordinator, Butte County Farm Bureau 

Navel Orangeworm Research Updates 

Dr. Emily Symmes, UCCE IPM Advisor, Sacramento Valley 

Early Season Irrigation: Do We Know When to Start? 

Dr. Ken Shackel, Department of Plant Sciences, UC Davis 

Lunch 

Botryosphaeria and Band Canker update 

Dr. Themis Michailides, UCCE Plant Pathology Specialist, 

Kearney Agricultural Research and Education Center 

Weed Management in Young Orchards 

Dr. Brad Hanson, UCCE Weed Specialist, UC Davis 

Adjourn 

In Conjunction with the UCCE Butte/Glenn/Tehama 

Counties Almond & Walnut Day 



25



leafhoppers is primarily due to changes 

in vine vigor rather than any increase 

in biological control. While cover crops 

are in some cases used to moderate 

vine vigor, in many situations this can 

be achieved much more economically 

by adjusting irrigation regimes, soil 

amendments and pruning practices. 

Landscape Diversity 

Given the importance of overwintering 

habitat to Anagrus parasitoids and the 

dismal performance of cover crops, 

researchers have more recently started to 

focus on the relationship between landscape 

diversity and biological control of 

vineyard leafhoppers. Landscape diversity 

can be defined in many nuanced ways, 

but generally refers to the quantity of 

natural habitat that falls within a larger 

radius surrounding the vineyard (for 

example, the total area of all riparian 

habitat within two miles of a vineyard). 

Recent studies in the North Coast evaluated 

biological control of leafhoppers in 

multiple vineyards located in contrasting 

low and high diversity landscapes. 

Vineyards in high diversity landscapes, 

with lots of natural habitat within one 

third mile of the vineyard, tended to 

have more Anagrus parasitoids earlier in 

the season, which then led to increased 

leafhopper parasitism rates and lower 

late-season leafhopper densities (Wilson 

et al. 2015a, Wilson et al. 2017). While 

not all natural habitats necessarily 

harbor Anagrus overwintering habitat 

(i.e. coyotebrush and blackberry), these 

plants are more likely to be present in a 

high diversity landscape given that there 

is more natural habitat overall. 

In a related study, biological control 

of leafhoppers was evaluated in vineyard 

blocks that were close to (30 feet) 

and far away from (500 feet) riparian 

habitats. Since these areas harbor a lot 

of blackberry, it could be that Anagrus 

populations and leafhopper parasitism 

is greater on vines closer to the riparian 

area. Leafhopper densities were 

indeed lower on vines closer to the 

riparian areas, but this was once again 

due to changes in vine status rather 

than increased parasitism (Wilson et al. 

2015b). Similar to the cover crop studies, 

vines that were close to the riparian 

area tended to be less vigorous, most 

likely due to changes in microclimate 

and soil conditions associated with vine 

shading from the tall riparian vegetation 

and compacted dirt roads along the 

riparian border of vineyard blocks. 

Conclusion 

As you can see, almost all the vineyard 

habitat research to date has focused 

on leafhoppers, whereas growers are 

of course managing for a much wider 

range of pests, including mealybugs/ 

ants, sharpshooters, mites and thrips. 

Impacts of habitat diversification on 

these other pest species has simply not 

taken place yet. Very early research 

on Willamette mites (Eotetranychus 

willamettei) did find that Johnson grass 

(Sorghum halepense) could harbor 

alternate prey that supported Western 

predatory mites (Galendromus occidentalis) 

and led to lower Willamette mite 

densities on vines—but no economic 

program was ever developed for this 

pest. Beyond that, not much else is 

known about how habitat diversification 

influences other key grape pests. 

Research on habitat diversification 

to control vineyard leafhoppers has 

demonstrated the importance of 

overwintering habitat for Anagrus 

parasitoids and moderation of vine 

vigor. Alternately, cover crops do not 

appear to be a viable way of increasing 

biological control of leafhoppers. While 

their ability to reduce vine vigor can 

translate to some changes in leafhopper 

populations, there are other ways to 

moderate vigor that are more practical 

and cost-effective. Furthermore, vigor 

moderation in the absence of Anagrus 

overwintering habitat may still result in 

increased leafhopper densities, as it is a 

combination of early-season parasitism 

and moderate vine vigor that regulates 

leafhopper populations. 

Phacelia tanacetifolia blooming in a Napa County vineyard. 



A common legume/grass winter cover crop blend in a Napa County vineyard. 

Even with all the emphasis on leafhoppers, 

habitat diversification strategies 

that can produce consistent results for 

this pest remain elusive, and many key 

questions remain. How much Anagrus 

overwintering habitat is adequate? How 

far can these parasitoids migrate into 

vineyards? Does overwintering habitat 

need to be directly adjacent to the vineyard? 

And so on… 

In summary, specific habitat diversification 

practices that can produce 

consistent and economically relevant 

impacts on vineyards pests remain elusive. 

While in theory this is not entirely 

impossible to achieve, the reality is that 

a lot of additional research is certainly 

still needed at this point in time. 

References 

Costello, M. J., and K. M. Daane. 2003. 

Spider and leafhopper (Erythroneura 

spp.) response to vineyard ground cover. 

Environ. Entomol. 32: 1085-1098. 

Daane, K. M., and M. J. Costello. 1998. 

Can cover crops reduce leafhopper 

abundance in vineyards? Calif. Agric. 

52: 27-33. 

Daane, K. M., and L. E. Williams. 

2003. Manipulating vineyard irrigation 

amounts to reduce insect pest damage. 

Ecol. Appl. 13: 1650-1666. 

Daane, K. M., B. N. Hogg, H. Wilson, 

and G. Y. Yokota. 2018. Native grass 

ground covers provide multiple ecosystem 

services in Californian vineyards. J. 

Appl. Ecol. 

Doutt, R. L., and J. Nakata. 1965. 

Overwintering refuge of Anagrus epos 

(Hymenoptera: Mymaridae). J. Econ. 

Entomol. 58: 586-586. 

Doutt, R. L., and J. Nakata. 1973. The 

Rubus leafhopper and its egg parasitoid: 

an endemic biotic system useful 

in grape pest management. Environ. 

Entomol. 2: 381-386. 

Doutt, R. L., J. Nakata, and F. Skinner. 

1966. Dispersal of grape leafhopper 

parasites from a blackberry refuge. 

Calif. Agric. 20: 14-15. 

Hanna, R., F. G. Zalom, and W. J. 

Roltsch. 2003. Relative impact of spider 

predation and cover crop on population 

dynamics of Erythroneura variabilis in 

a raisin grape vineyard. Entomol. Exp. 

Appl. 107: 177-191. 

Kido, H., D. Flaherty, D. Bosch, and 

K. Valero. 1984. French prune trees as 

overwintering sites for the grape leafhopper 

egg parasite. Am. J. Enol. Vit. 35: 

156-160. 

Nicholls, C. I., M. P. Parrella, and M. 

A. Altieri. 2000. Reducing the abundance 

of leafhoppers and thrips in a 

northern California organic vineyard 

through maintenance of full season floral 

diversity with summer cover crops. 

Agric. For. Entomol. 2: 107-113. 

Roltsch, W., R. Hanna, H. Shorey, M. 

Mayse, and F. Zalom. 1998. Spiders 

and Vineyard Habitat Relationships 

in Central California, pp. 311-338. In 

C. H. Pickett and R. L. Bugg (eds.), 

Enhancing Biological Control: Habitat 

Management to Promote Natural Enemies 

of Agricultural Pests. University of 

California Press, Berkeley, California. 

Wilson, H., A. F. Miles, K. M. Daane, 

and M. A. Altieri. 2015a. Landscape 

diversity and crop vigor influence 

biological control of the western grape 

leafhopper (E. elegantula Osborn) in 

vineyards. PLoS ONE 10: e0141752. 


and M. A. Altieri. 2015b. Vineyard 

proximity to riparian habitat influences 

western grape leafhopper (Erythroneura 

elegantula Osborn) populations. Agric., 

Ecosyst. Environ. 211: 43-50. 


and M. A. Altieri. 2016. Host plant 

associations of Anagrus spp. (Hymenoptera: 

Mymaridae) and Erythroneura 

elegantula (Hemiptera: Cicadellidae) in 

northern California. Environ. Entomol. 

45: 602–615. 


and M. A. Altieri. 2017. Landscape 

diversity and crop vigor outweigh 

influence of local diversification on 

biological control of a vineyard pest. 

Ecosphere 8. 

Wilson, L. T., C. H. Pickett, D. Flaherty, 

and T. Bates. 1989. French 

prune trees: refuge for grape leafhopper 

parasite. Calif. Agric. 43: 7-8.Laborupt 






27


atquunt utaquae lis dolestintius aliquam 

nonseri omniam quatem. Iminto 

officipitas eossit invent aut ipsantiam, ut 

magnatem quunt officiis accae officiatiur 

archicilis niae volupta tiisque volut 

veliber essit, is simaximusda volum 

quis net, voluptatur sinvene ctaquis 

illaborem alitate parum re non nam et 

harionsedis eium quuntiu sanihil et, unt 

quia quo magnienimus, volore omnis 

All photos courtesy of Cecilia Parsons. 

simi, aut quosti ipiet fugiatiam hiligent 

in pellor autemporrum ellam etur moloriti 

omnis minvent velessit quis magnita 

Improving Grape 

nisit, cus adis ma suntorios sum ant 

que endandae. Pid mos simporem eos 

esequiam rerum volupti onsequa esserumquis 

dolorepudis porioris exernat 

Coloration and Ripening 

urempe cus molest laboritatur, ut re nos 

magnis dit vent ratus voluptatus maiorpores 

autate as millaut atibeat uriorup 

tature sit ullicae sectiam simin premque 

volor si rate cum eum alique vel 

Using the Plant Hormone 

iusdantis alique exceritaquo eum alitius 

atur? Qui unti tectis apictur, omnis aut 

et ex eria doluptas moles eume nossimu 

sdanisit volupta quaspisquam re enda 

nobit laut expernat. 

Ethylene 

Accus. Asinum in remodis as et quature 

dictates volloratqui consend iorestis 

maio berit eat et hicid quas dolectu 

repudic tem veritio velluptur? 

Ut qui dolesec tempersperio ditas mil 

By: Cecilia Parsons |Associate Editor 

earumet voluptum sandit hictatis ut 

aspietur mollorit volo torunt, tet adiam 

landest voluptae vid mo volorem atiur, 

te nonescillam nus, ipidundit, te nus es 

et rem fugit incte corat eos anditas re 

volorem fugia quis quisciam es minulla 

dellace ssunti re venet officium fuga. 



Value of red table grape varieties is dependent upon berry 

color. Achieving the desired red hues at harvest is the 

goal for growers seeking premium prices for their crop. 

Numerous Factors Affect Coloration 

University of California Cooperative Extension viticulture 

advisor Ashraf El-Kereamy in Kern County said there are many 

factors that can affect coloration and are used on red seedless 

table grape varieties. 

Red table grape varieties such as Crimson Seedless and Flame 

Seedless, under certain conditions, may require help in coloring 

while some new varieties of red table grapes develop color 

without assistance. Flame and Crimson are popular varieties, 

El-Kereamy said, and still in favor with growers due to their harvesting 

time—the varieties need a little more attention to bring 

out the color. 

The red, purple and black colors in table grapes are due to the 

plant pigments, anthocyanins. These pigments are derived 

from the basic products of photosynthesis and are converted by 

enzymes to flavonoids and coupled to sugar molecules by other 

enzymes yield the final anthocyanin pigments. 

Disruption in any of the enzyme mechanisms by genetic, environmental 

or cultural practices could alter anthocyanin production 

and affect berry coloration. 

Lack of Color at Harvest 

What causes disruption and subsequent lack of grape color at 

harvest is complicated. El-Kereamy said red coloration is under 

hormonal control that is influenced by several factors. Some 

can contribute to optimal berry coloration, other factors, which 

may be out of the control of the grower can contribute to lack of 

color. 

Use of nutrients or supplements as a part of a vineyard management 

plan can effect color due to composition or mode of 

action if they are applied at the critical stage for anthocyanin 

induction and development. 

Nitrogen and Potassium 

Nitrogen (N) and potassium can influence grape color and 

must be managed. Moderate nitrogen supply before bloom and 

moderate potassium during veraison can help in optimizing 

anthocyanins. However, excessive N can have a negative effect 

on color. Fruit ripening and coloration can be delayed by too 

much applied nitrogen. Determining the optimal amount of N 

for vine growth without over application is essential. Foliar potassium 

application can boost grape anthocyanin accumulation 

and coloration, but it can reduce berry size in some cases. 

Deficit Irrigation 

El-Kereamy said deficit irrigation at the proper time can 

assist in bringing on berry color. 

A study funded by the California Table Grape Commission 

found total berry skin anthocyanin contents and individual 

pigment compounds increased with deficit irrigation at two 

experimental sites in Coachella and San Joaquin valleys. 

Deficit irrigation induced expression of several genes involved 

in anthocyanin accumulation. 

Other Cultural Practices 

There are some other cultural practices growers can use to 

improve berry color. Large, dense canopies that prevent 

light from reaching the developing fruit can stall berry 

coloration. The cultural practice of shoot and leaf removal 

to allow more light to reach the fruit can help with coloring. 

Vine nutrition and rootstock selection also effect canopy 

size, contributing to color determination. 

Plastic covers on grapevines are used to protect them from 

rain events and extend harvest. Transparent or green plastic 


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covers are used with red varieties to let 

in light and assist with coloration. 

Red table grapes grown on sandier soils 

will color more than the same varieties 

grown on heavier soils, El-Kereamy 

said. 

Temperatures have a significant effect 

on anthocyanin biosynthesis and accumulation. 

Anthocyanin biosynthesis 

increases with temperature until the 

maximum of 95 degrees F. Temperatures 

above 95 reduces anthocyanin 

biosynthesis and degradation is increased 

causing poor red coloration. 

Water management and building a good 

early season canopy can help overcome 

the negative effect of high temperatures. 

Grape anthocyanin biosynthesis and 

accumulation are best when nighttime 

temperatures are below 73 degrees F. 

This presents a problem for growers in 

the Coachella Valley and some southern 

parts of the San Joaquin Valley. 

Ethylene 

El-Kereamy’s studies on anthocyanin 

in grapes demonstrated that grapes 

produce a small amount of the ethylene 

at veraison which induces expression of 

genes and starts anthocyanin accumulation 

in red grapes. Internal ethylene 

concentration in grapes affects anthocyanin 

and color. An external source of 

ethylene releasing compounds applied 

to grapes causes an increase in internal 

ethylene and also activates anthocyanin. 

According to El-Kereamy the high 

temperatures inhibit the coloration due 

to hormonal changes that act against 

activation of anthocyanin biosynthesis 

genes. 

Abscisic acid 

Another plant hormone known for 

its role in anthocyanin biosynthesis is 

abscisic acid or ABA. An increase in 

the ABA content of berries coincides 

with veraison and red color initiation in 

grapes. The application of ABA at 



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31



veraison also stimulates anthocyanin biosynthesis. Commercial 

products that contain an ethylene releasing 

compound or ABA as the active ingredient are commonly 

used in vineyards to improve color. El-Kereamy said that 

attention should be given to varietal differences, timing of 

the application and other cultural practices during the application. 

Practices or conditions that suppress the internal 

concentration of ethylene will result in poor coloration. 

Ethephon 

The commercial product Ethephon is standard practice for 

table grape growers who need help with color. Ethephon 

is a plant growth regulator used to promote fruit ripening, 

abscission, flower induction, and other responses. It 

is applied as a tank spray. It moves inside the berries and 

releases ethylene and activates anthocyanins biosynthesis. 

It does not have an effect on berry size, El-Kereamy said. ProTone 

is the commercial product with ABA and it can be mixed with 

Ethephon and used as a spray application for color. Both of these 

products are plant growth regulators. Other plant growth regulators 

gibberellic acid and cytokinins are known for their effects on 

ethylene and ABA and have a negative role in coloring grapes. 

Ethephon is listed as a pesticide, El-Kereamy said, and must 

be used according to the label. There is a re-entry period and 

Pre-harvest interval period. That requirement makes timing an 

application tricky. The spray is applied at color break stage, not before. 

You want to be ‘pushing the color,” El-Kereamy said. Quality 

of the fruit can be affected if applied too close to harvest. 

Comments about this article? We want to hear from you. 

Feel free to email us at article@jcsmarketinginc.com 


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View of the Ranch Fire on the first day where many vineyards 

were damaged. All photos courtesy of Glenn McGourty. 

The Impacts of 

Smoke to Vineyards 

By: Glenn McGourty | Winegrower and Plant Science Advisor, UCCE 

Mendocino and Lake Counties 



Smoke Damage in Vineyards 

California and the Pacific Northwest 

have endured one of the 

worst fire seasons on record in 

2018. The huge areas burned, loss of 

buildings and life have been horrific. A 

combination of tinder dry vegetation, a 

prolonged dry season and lack of rain 

that would normally be expected in 

autumn have created “perfect storm” 

conditions that have scorched over a 

million acres, left communities completely 

destroyed, numerous lives lost 

and displaced thousands of people. 

Impacts are being felt far beyond the 

fire zone as smoke creates the most 

unhealthy air quality conditions across 

the state ever measured. 

The smoke from fires can also greatly 

affect wine grape and wine quality in 

close proximity to burn areas (which 

seems trivial compared to the loss of 

property and life). 

Direct Impacts of Fire on 

Vineyards 

Forest and brush fires have the potential 

to harm vineyards, wine grapes and 

wine in several different ways. The most 

damaging event is when vineyards 

actually catch fire and burn. This 

happens mostly to small vineyards 

surrounded by brush and forest. If 

you are concerned about fires in this 

situation, it is a good idea to minimize 

the vegetation on the vineyard floor 

either by cultivating the vineyard so that 

the soil is bare, or mowing very close to 

the ground early in the growing season 

to reduce any dry material. Removing 

brush, mowing and managing the 

landscape to risk damaging fires close 

to the vineyard is advisable. Cal Fire 

has recommendations to make your 

area reasonably fire safe that centers 

on eliminating low growing brush and 

vegetation to prevent the fire from 

climbing into the crown of trees if you 

live in a forested area. Increasingly, 

control burns during low danger 

fire conditions are being discussed 

and implemented, but for now it is 

just beginning to be used as a fire 

prevention tool. 

The next most devastating problem is 

when the edges of the vineyard either 

burn or are exposed to superheated 

air from the flames that essentially 

cook the vascular system of the vines 

and wilt the fruit. Wine grapes are not 

adapted to fire having originated from 

riparian areas (unlike so many of our 

California natives, which depend on fire 

for propagation and renewal). The bark 

is very thin, and provides no insulation 

from heat. The overall mass of the wood 

in the vine is relatively small, so even 

internal cells found in the woody xylem 

are likely to die from heated sap that 

might actually boil when exposed to hot 

air accompanying a fire. Vines damaged 

by fire or heat rarely recover—if the 

vines are either charred or the leaves 

are completely desiccated, odds are 

the vines have been severely damaged 

and are not going to return to healthy 

growth. You may see some buds push, 

but often the vascular system of the 

vines is seriously compromised in the 

woody portions, and there is likely to be 

irreversible damage. Check the vines by 

cutting into the cambium, and inspect 

the health of the xylem and phloem. 

Using a hand lens or microscope, 

you can detect damage by obvious 

discoloration (grey or brown instead 

of green) and wilting in the cambium. 

Cut into lateral buds to see if they are 

still green and viable. You can wait and 


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A damaged vineyard from the Valley Fire in Lake County. The 

vineyard actually burned and melted the drip line, but one 

month later, the vines are resprouting. 


see how the vines push the following 

growing season, and retrain vines if 

needed. If damage appears minimal, 

you can prune during the following 

winter and see how the vines push the 

following growing season, retraining 

vines if required by removing damaged 

parts. 

Smoke and Vineyards 

During a forest fire, large volumes of 

smoke are produced that can travel 

many miles and inundate valleys, 

especially at night when cold air 

settles into low lying areas. Smoke 

contains visible airborne byproducts of 

combustion, made up of water vapor, 

particulates (including tar, ash, carbon 

and partially burnt fuel fragments), 

and many gases (CO2, CO, N2O, S2O, 

NH3, CH4, NOx, ozone, and other nonmethane 

hydrocarbons.) Smoke makes 

up about 1.5-2 percent of the material 

that has burned. 

Smoke flavors in wine result from 

smoke following the combustion of 

lignin in wood, resulting in phenolic 

compounds released into the air. Wood 

is composed of about 20-30 percent 

lignin, which gives wood strength and 

lines water conductive tissues. Guaiacol 

and 4-methylguaiacol are compounds 

associated with smoke. Both are 

chemicals that we can taste in smoked 

food flavoring. These compounds can be 

found in oak barrels during the toasting 

process. On their own, these two 

chemicals have flavor profiles described 

as “bacon, burnt bacon, smoky, leather, 

spicy, phenolic, and spicy, salami, and 

smoked salmon” which doesn’t sound 

so bad (isn’t everything better with 

bacon!) The problem is that there are 

more than 70 other compounds in 

forest fire smoke known as glycosides 

that produce very undesirable flavors 

and odors that are described as, “like 

licking an ash tray, burnt garbage, a 

burnt potato, a campfire that has been 

drenched with water.” 

When grape vines are exposed to 

fresh smoke, the phenolic compounds 

concentrate in the skins of the fruit, 

more than in the pulp and the juice, 

and also in the leaves. They conjugate 

with sugars, and are released during 

fermentation. Both guaiacol and 

4-methylguaiacol can be detected in 

the fruit by gas chromatography, so it is 

possible to sample fruit before harvest 

to make picking decisions. While these 

compounds aren’t necessarily the sole 

cause of smoke flavors, they are highly 

correlated to many other compounds 

(the glycosides) that cause the wine 

to taste bad. Glycosides are not easy 

to test for as a group, and at this time, 

no commercial lab in the US is able to 

test for these smoke compounds likely 

to be in the fruit and wine. There are 

protocols in place to test fruit before 

picking, and anything found to have 

more than 0.5 parts per billion (ppb) 

guaiacol is considered likely to have 

smoke flavor problems. Sampling 

whole berries is recommended, as 

the skins of the berries have the 

highest concentration of guaiacol and 

4-methylguaiacol compared to juice. 

Whole berry test results indicate that 

levels between 0.5 ppb to 2.0 ppb are 

moderately affected, and will require 

special handling and treatment in the 

winery. Levels above that are almost 

certainly going to have major problems 

with smoke flavors, and may be cause 

for rejection by the winery, especially 

for red fruit. During fermentation, the 

glycosides are released when yeasts 

metabolize the sugars leaving the smoke 

compounds behind. This may increase 

their concentration 6 to 10 times. 

No doubt the intensity and duration of 

smoke plays a factor. We noted locally 

that not all vineyards were equally 

affected, and why this occurred, and 



the pattern of smoke affected vineyards 

remains a bit of a mystery. 

Wine grapes are most likely to be 

affected if your vineyard is close to a 

large fire and is inundated with intense 

smoke. Many of the smoke flavor 

compounds are volatile, and are most 

likely to affect fruit for a relatively 

short period of time, as little as two 

hours after combustion. However, these 

compounds move readily with wind, 

and can travel some distance from the 

source of the fire, as much as four or 

five miles. Australian researchers have 

shown that there is little guaiacol or 

4-methyl guaiacol in ash that might 

settle on your fruit. Researchers were 

unable to remove guaiacol from the 

fruit by washing or rinsing with any 

solvents. However, removing the leaves 

from around the fruit, high volume 

and high pressure washing with water 

before harvest did seem to help reduce 

smoke flavors in the wine. By contrast, 

if you are in a confined valley, and 

smoke settles as an inversion layer for 

a day or two from a distant fire, it is 

less likely that you will have issues with 

off flavored fruit. At that point, the 

smoke is composed mostly of very small 

particulate matter, less than 10 microns 

in size. 

Varieties also differ as to how much 

smoke that they will absorb and 

the extent of off flavors that result. 

Experiences in California, Canada 

and Australia suggest that the most 

affected varieties in decreasing order 

are Sangiovese> Pinot noir> Cabernet 

sauvignon> Chardonnay > Sauvignon 

blanc> Syrah >Merlot> Petite Sirah. 

Conclusion 

Off flavors to wine grapes and wine 

are part of the collateral damage from 

large wild fires. Research is underway 

to better understand the dynamics of 

how smoke flavors are acquired by fruit. 

Maybe even more important is research 

into techniques that can fix off flavors 

caused by smoke when the fruit is made 

into wine. A certainty is that in the 

changing climates of our wine growing 

regions, more fire and smoke will occur. 


to hear from you. Feel free to email us 

at article@jcsmarketinginc.com 

A month after these vines were burned in the Valley Fire in Lake County 

and they are most likely dead. 

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37


All photos courtesy of George Zhuang. 

Field Evaluation of Seven Rootstocks 

Under Saline Condition 

By: George Zhuang and Matthew Fidelibus | University of California Cooperative Extension, Fresno 

County | Department of Viticulture and Enology, University of California (UC) Davis 

Background 

The San Joaquin Valley (SJV including 

crush district 11, 12, 13, 

and 14) contains 40 percent of 

the wine grape acreage and crushes 70 

percent of California wine grapes (California 

Grape Acreage Report and Grape 

Crush Report 2016). Due to the pest 

threats from nematodes and phylloxera, 

grapes planted in the SJV are usually 

grafted on nematodes or phylloxera 

resistant or tolerant rootstocks. The 

commercial standard rootstocks for 

the SJV winegrowers are Freedom and 

1103P. Freedom rootstock has high root 

knot nematode and medium phylloxera 

resistance. High scion capacity makes it 

a popular rootstock for the high per acre 

yield in the SJV. However, vines on Freedom 

tend to accumulate high levels of 

potassium (K) in their fruit, which can 

in turn lead to undesirably high juice 

pH. Further, it has relatively low salt 

tolerance compared to other rootstocks, 

and is thus not the best choice for some 

SJV vineyards (Christensen 2003). 

1103P rootstock has both high phylloxera 

and root knot nematode resistance 

with the medium salt tolerance. These 

characteristics make it good rootstock 

for sites with moderately saline soil and 

irrigation water (Christensen 2003). 

Other common rootstocks have been 

used in SJV vineyards are Ramsey (Salt 

Creek), 140Ruggeri, and Schwarzmann. 

Ramsey has high phylloxera and root 

knot nematode resistance and high salt 

tolerance. However, Ramsey is difficult 

to propagate (Christensen 2003). 140Ru 

has high phylloxera resistance and 

high salt tolerance with low root knot 

nematode resistance and low K uptake 

(Christensen 2003). As a comparison, 

Schwarzmann has high phylloxera 

and medium root knot nematode 

resistance with medium salt tolerance 

(Christensen 2003). 

GRN rootstocks have been bred by 

Dr. Andy Walker in UC Davis and 

were under field evaluation at different 

locations around California to quantify 

the nematode resistance and viticultural 

performance of scion variety. There 

are currently five GRN rootstocks: 

GRN-1, GRN-2, GRN-3, GRN-4, and 

GRN-5. Previous field trials of GRN 

rootstocks have focused on nematode 

resistance and viticultural performance 

of scion variety. However, there is 

a lack of information on their salt 

tolerance under the field condition. The 

preliminary research results from a field 

trial in the northern SJV showed that 

the GRN-1, -2 and -3 yielded similarly 

as Freedom and 1103P rootstocks with 

adequate harvest juice Brix (personal 

communication from Dr. Andy 

Walker). Grapevines generally show 

reduced vigor and yield when the soil 

electrical conductivity (EC) is above 

2.5 dS/m (Christensen 2000). Specific 

salts, like sodium (Na), chloride (Cl) 

and boron (B), causing toxicity of 

grapevines. High Na (>690 ppm), Cl 

(>350 ppm), and B (>1 ppm) levels in 

soil start to cause the significant toxicity 

and ultimate damage on the grapevines 

(Figure 1, see page 40) (Christensen 

2000). 

Although it has been widely recognized 

that high soil salinity can significantly 

impact the vine growth and per acre 

yield, there is limited information on 

fruit quality and wine chemistry as well 

as wine sensory traits. Loryn, et al. 2014 

indicates that NaCl accumulated in 

berries can have a negative impact on 

juice and wine sensory characteristics 

with the detection threshold value 

of NaCl in wine as low as 0.31 g/L in 

Australia. 

Pinot gris on seven rootstocks were 

compared in a commercial vineyard 



39



with saline water and soil near Cantua 

Creek in Fresno County during 2017 

and 2018. Rootstocks were planted 

in 2015 with field grafting during the 

dormant season. Data collection started 

with the first harvest season of 2017 

and continued in 2018. Five vines were 

flagged in the field and labeled as one 

data point. As for each data point, leaf 

nutrients, yield components and juice 

chemistry were measured for both years 

as well as pruning weight during the 

dormant season. Three data points per 

rootstock were randomly selected and 

results were presented as the average. 

The salt/drought tolerance information 

of selected rootstocks included in this 

study was described in the Table 1. 

Results 

Figure 1. Boron toxicity on Pinot gris with leaf margin necrosis. 

Petioles and leaf blades were sampled 

at veraison in 2017, and bloom, 

veraison and harvest in 2018. Large 

variation has been observed for petiole 

NO3-N across two years (Figure 2, 

see page 41), and petiole NO3-N 

can be affected by various factors, 

e.g., fertilizer application, timing of 

sample collection, and weather on the 

particular day of collection. Therefore 

it is difficult to draw the conclusion on 

one year’s data. However, the difference 

of petiole NO3-N by rootstocks was still 

consistent with higher petiole NO3-N 

from 140Ru and Ramsey in both 

2017 and 2018. High petiole NO3-N 

is usually associated with high shoot 

vigor. Results of petiole K were similar 

to the results of petiole NO3-N. Petiole 

Cl was tested in 2018 only and 1103P, 

140Ru and Schwarzmann showed 

lower Cl (Figure 3, see page 41). Lower 

Table 1. Salt/drought tolerance info of rootstocks included in this study. 

Table 1. Salt/drought tolerance info of rootstocks included in this study. 

petiole Cl is regarded as beneficial 

for grapevine’s growth and yield, 

since higher Cl reduces leaf stomatal 

conductance, and therefore decrease 

photosynthesis, yield and berry sugar 

accumulation. Certain rootstocks, 

e.g., 1103P, 140Ru, Schwarzmann and 

Ramsey, have been recommended 

as salt-tolerant rootstocks due to the 

lower Cl uptake (Christensen 2003; 

Cox, 2009). Our results were largely 

Rootstock Parentage Drought tolerance 1 Salt tolerance 

1616C V. longii V. riparia Low Medium 

Schwarzmann V. riparia V. rupestris Medium Medium 

140Ruggeri V. berlandieri V. rupestris High Medium-High 

Ramsey (Salt 

V. champinii Medium-High High 

Creek) 

1103Paulsen V.berlandieri V. rupestris Medium-high Medium 

GRN-1 V. rupestris V. rotundifolia 

‘Cowart’ 

GRN-2 

GRN-3 

((V. rufotomentosa x (Dog Ridge x 

Riparia Gloire)) x Riparia Gloire 

((V. rufotomentosa x (Dog Ridge x 

Riparia Gloire)) x V. champinii 

c9038 

GRN-4 ((V. rufotomentosa x (Dog Ridge x 

Riparia Gloire)) x V. champinii 

c9038 

1 

drought tolerance and salt tolerance are cited from Christensen 2003. 


? ? 

? ? 

? ? 

? ?


in line with those studies. Boron was one of the targets in our study, since the 

experimental site has relatively high soil and water boron content (soil boron of 

0.5-0.7 ppm in 2018). Less difference of petiole B was found by rootstocks (Figure 

4), and currently less information was available in terms of B tolerant rootstocks. 

However, 1103P and GRN3 rootstocks had relatively lower petiole B as well as 

blade B (data not shown), and there was an increase of petiole B from 2017 to 2018, 

and it might be largely due to less leaching water available from the dry winter of 

2017. Similar yield was found across rootstocks at the first harvest of 2017, with 

the exception of 1103P. Yield was generally higher in 2018 than it in 2017 with 

more mature vines, however, GRN2 and GRN3 yielded the most across rootstocks 

(Figure 5). Higher vigor and canopy size might contribute to the higher yields. 

Rootstocks did not affect Brix, pH or titratable acidity (TA), however, we did find 

a large variation from season to season with higher Brix and TA, lower pH in 

2018 than these in 2017 (Figure 6, see page 42). Surprisingly, there was a stronger 

correlation between Na and pH in juice, with higher Na associated with higher pH 

(Figure 7, see page 42) than there was for petiole K, juice K or juice pH (Figure 

8, see page 42). More data are needed to determine if Na-excluding stocks can 

consistently maintain lower fruit juice pH on salty sites. Boron is unique among 

the micronutrients because of the narrow acceptable range of soil B levels that fall 

between deficiency and excess (toxicity) (Christensen 2000). In our study, petiole B 

across rootstocks is around the critical value of 80 ppm, and good correlation has 

been found between petiole B and berry weight as well as the total yield (Figure 9, 

see page 42). This result evidently indicates petiole B exceeding critical value might 

result in smaller berry and ultimately, the yield loss. 

Petiole NO 3 

-N (ppm) 

2500 

2000 

1500 

1000 

500 

0 

2017 

2018 

Rootstock 

Veraison 

1103P 140R 16-16 GRN2 GRN3 RamsSchwarz 

Rootstock 

Veraison 


Figure 2. Petiole NO3-N by 

Figure 2. Petiole NO 3-N by rootstocks (2017/2018) Figure 3. Petiole 

Figure 

Cl 

3. 

by 

Petiole 

rootstocks 

Cl by 

(2017) 

rootstocks 

rootstocks (2017/2018) 

(2017) 

Petiole B (ppm) 

110 

100 

90 

80 

70 

60 

2017 

2018 

Veraison 

Petiole Cl (%) 

Yield (t/acre) 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0.0 

10 

8 

6 

4 

2 

2018 

2017 

2018 

Summary 

Seven rootstocks have been 

compared in 2017 and 2018 for 

plant nutrition, yield and harvest 

fruit chemistry. Previously 

regarded salt-tolerant rootstocks, 

e.g., 1103P, 140Ru, Ramsey, 

perform as expected with lower 

petiole Cl content and our data 

was largely in line with previous 

results. So far, rootstocks in our 

study had significant impact on 

plant nutrition, yield and canopy 

size, measured as pruning weight, 

however, less impact on harvest 

fruit chemistry. Interestingly, 

GRN 2 and 3 rootstocks which 

accumulated the most petiole Cl, 

had the highest yields and pruning 

weight (data not shown), and more 

years’ data are needed to confirm 

the long-term impact. In terms of 

Boron, none of those rootstocks had 

significant impact on B uptake and 

higher petiole B has caused smaller 

berry and ultimately, yield loss in 

our study. This rootstock trial is still 

on-going and GRN 1 and GRN 4 

rootstocks will be included in the 

following years’ study. 

Acknowledgment 

Study in 2018 was funded through 

California Grape Rootstock 

Improvement Commission and 

supported by industry collaborators. 

Reference 

California Grape Acreage 

Report. 2016. https://www.nass. 

usda.gov/Statistics_by_State/ 

California/Publications/Specialty_ 

and_Other_Releases/Grapes/ 

Acreage/2017/201704gabtb00.pdf 

California Grape Crush Report. 

2016. https://www.nass.usda.gov/ 

Statistics_by_State/California/ 

Publications/Specialty_and_ 

Other_Releases/Grapes/Crush/ 

Final/2016/201603gcbtb00.pdf 

50 


Rootstock 

0 


Rootstock 

Figure 4. Petiole 

Figure 

B 

4. 

by 

Petiole 

rootstocks 

B by 

(2017/2018) 

rootstocks 

Figure 5. 

Yield Figure (tons/acre) 5. Yield by (tons/acre) rootstocks (2017/2018) by 

(2017/2018) 

rootstocks (2017/2018) 

Christensen, P., Dokoozlian, N., 

Walker, A., and Wolpert, J. 2003. 

Wine Grape Varieties in California. 

University of California Agriculture 




41


30 

28 

26 

2017 

2018 

4.2 

4.0 

2017 and 2018, r=0.89 


and Natural Resources Publication 

3419. 

TSS (Brix) 

24 

22 

20 

Juice pH 

3.8 

3.6 

Christensen, P. 2000. Raisin 

Production Manual. University of 

California Agriculture and Natural 

Resources Publication 3393. 

18 

16 


3.2 

0 10 20 30 40 50 60 

Rootstock 

Juice Na (mg/L) 

Figure 6. TSS Figure (Brix) 6. by TSS rootstocks (Brix) by (2017/2018) rootstocks Figure 7. 

Juice Figure pH and 7. Juice juice Na pH content and juice (2017/2018) Na 

(2017/2018) 

content (2017/2018) 

Harvest juice K (mg/L) 

8000 

7000 

6000 

5000 

4000 

3000 

2000 

1000 

2018, r=0.55 

0 

0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 

Berry weight (g) 

3.4 

0.6 

50 60 70 80 90 100 

Harvest petiole K (%) 

Veraison petiole B (ppm) 

Figure 8. Petiole K and juice K (2018) 

Figure 8. Petiole K and juice K (2018) 

Figure 

Figure 

9. 9. 

Petiole B and berry weight (2018) 

Petiole and berry weight (2018) 

1.2 

1.1 

1.0 

0.9 

0.8 

0.7 

2018, r=0.83 

Loryn, L.C., Petrie, P.R., Hasted, 

A.M., Johnson, T.E., Collins, C., and 

Bastian, S.E.P. 2014. Evaluation of 

sensory thresholds and perception of 

sodium chloride in grape juice and 

wine. American journal of Enology and 

Viticulture. 65:1. 

Cox, C. 2009. Rootstocks as a 

management strategy for adverse 

vineyard conditions. The Grape and 

Wine Research and Development 

Corporation: Water & Vine – Managing 

the challenge. Fact sheet No. 14. 

(The Grape and Wine Research and 

Development Corporation: Adelaide, 

Australia). 


to hear from you. Feel free to email us 

at article@jcsmarketinginc.com 


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www.wrtag.com43


An Online Forum to Facilitate Communication and 

Information Exchange Regarding California Citrus 

By: Dr. Greg W. Douhan | University of California Cooperative Extension, UCCE Citrus 

Advisor, Tulare, CA 

The University of California Cooperative 

Extension office in 

Tulare California is launching a 

new website (cacitrusnetwork.com) to 

facilitate exchange of information among 

individuals involved in citrus production 

in California from growers to academics. 

The ideology within this forum is to 

allow people within the field to exchange 

information in real time. It has been my 

personal observation, for example, that 

many pest control advisors (PCAs) have 

their own small network of individuals 

that they confide in regarding specific 

issues and often talk amongst themselves. 

It is my belief that having an internet-based 

forum would allow individuals 

to broaden this ‘in house group’ to all 

individuals involved in the industry to 

better communicate ideas, information, 

and concerns regarding various aspects 

of citrus production. The forum site is set 

up to deal with the various citrus regions; 



Figure 1. Screen shot of the main forum page on the cacitrusnetwork.com. 

All photos and graphs courtesy of Greg Douhan.

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45

Photo 1—Shows damage is caused by Colletotrichum 

species—a disease called twig and shoot dieback of citrus. 

Figure 2. Example posting of citrusguy1 including text and a picture of the issue 

he is observing in the field. Other users can then respond to this post to start a 

thread on the potential problem to try and solve the issue. 


San Joaquin Valley (SJV), Desert, Coastal, Southern Interior, 

and Sacramento Valley. The specific areas set up 

thus far are; Pests, Diseases, Irrigation, Fertility, Weeds, 

Harvesting Issues, and Postharvest Issues (Figure 1, 

see page 44). Two additional sections have also been 

set up for discussions: a general citrus area and posting 

dealing with all issues related to Asian Citrus Psyllid 

(ACP)/ Huanglongbing (HLB). Users will also be able 

to upload pictures taken from the field when posting a 

question (Figure 2). 

Benefits of the Forum 

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The utility of this forum is that a person has the ability 

to make an observation in the field, snap a couple 

of pictures of what he/she saw, and easily post this 

information to the forum where the citrus community 

at large could view and respond to start a thread on 

the topic. This could be done out in the field using a 

smart phone or tablet or from an office computer at 

the user’s leisure. The success of this network will rely 

on individuals in the citrus industry to utilize this 

new important tool. The site is up and running but is 

certainly in the beta-testing phase. Therefore, having 

individuals using the site and reporting any problems 

or making suggestions on making it better is highly 

desirable; this can be done by emailing or calling Dr. 

Greg W. Douhan who is the administrator of the forum 

(contact information on the website). The site has also 

been set up with security in mind so it will take a new 

user around a working day to receive an email to join 

because initially this was not done and the website 

was hacked with random postings that had nothing 

to do with citrus. Users can also set up their accounts 

to remain anonymous if they choose via a random 

username or they can inform who they are with 

contact information when a posting is made. If the 

forum is successful, support will be sought to produce 

an app for smart phones to make the process easier 

than a web-based forum. 

Comments about this article? We want to hear from you. 

Feel free to email us at article@jcsmarketinginc.com 


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