Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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THE EFFICACY AND CROP TOLERANCE OF PREEMERGENCE APPLICATIONS OF
SULFOMETURON PLUS HEXAZINONE TO CHRISTMAS TREES. L.J. Kuhns and
T.L. Harpster, The Pennsylvania State Univ., University Park.
ABSTRACT
Weed control and the tolerance of Douglas fir (Pseudotsuga menzesii (Mirb)
Franco) Christmas trees to two ratios of sulfometuron and hexazinone were evaluated.
Westar is a commercially formulated combination of sulfometuron and hexazinone in a
1:10 ratio, respectively. The same products were mixed in a 1:20 ratio to compare the
weed control and crop tolerance of the two combinations. The rates listed in Table 1
were applied on April 20, 2006, around trees at Unangst Tree Farm, Northampton
County; and Elizabeth Farms, Lancaster County; Pennsylvania. The trees at the two
farms were 4-5 and 3-4 feet tall, respectively. The buds were beginning to swell and
show some color at both sites. All applications were direct sprayed with a CO 2 test plot
sprayer, at 30 PSI in 24 GPA. An OC-02 nozzle was used and both sides of each row
were sprayed, with the lower 6-12 inches of all trees intentionally contacted. The air
and soil temperatures were 70-81 and 60 F, respectively. Each treatment was
replicated four times with eight to ten trees per replication. Weed control and plant
quality were rated on May 31 and July 18, 6 and 13 weeks after treatment (WAT).
Because glyphosate and simazine had been applied to the field the previous fall,
the Unangst site had very few weeds, even in the untreated plots. The predominant
weeds in the control plots were common lambsquarters (Chenopodium album L.), oxeye
daisy (Chrysanthemum leucanthemum L.), redroot pigweed (Amaranthus
retroflexus L.), and yellow foxtail (Setaria glauca (L.) Beauv.). At Elizabeth Farms
established perennial weeds and weed seedlings were present at the time of the first
application. The predominant weeds were common dandelion (Taraxacum officinale
Weber in Wiggers), Canada thistle (Cirsium arvense (L.) Scop.), common ragweed
(Ambrosia artemisiifolia L.), redroot pigweed, yellow foxtail, yellow nutsedge (Cyperus
esculentus L.), and downy brome (Bromus tectorum L.).
Six WAT all treated plots at both farms exhibited almost total weed control,
except those treated with sulfometuron plus hexazinone at 0.023 and 0.469 (Table 1).
At 13 WAT, the treated plots at Unangst Farm were still almost totally weed free, with
only a few foxtails and Johnsongrass breaking through. At Elizabeth Farms weed
control ratings were lower and less consistent. The two higher rates of both ratios
provided good control, but the lower rates provided marginally acceptable control. Both
broadleaf and grass seedlings were emerging in all treated plots. The higher rates
effectively controlled common ragweed, yellow woodsorrel, white clover, common
dandelion, ox-eye daisy, redroot pigweed, and velvetleaf.
Plant quality at both farms was uniformly good to excellent (Table2). Only the
high rate of the 1:20 ratio, at Elizabeth Farms, significantly reduced the quality of trees.
Injury consisted of some needle stunting and yellowing new growth. At Unangst Farm,
tree quality improved between the first and second evaluations, suggesting some of the
injury noted may have been from the fall glyphosate treatment. In conclusion, the
commercially formulated mix of sulfometuron and hexazinone at the 1:10 ratio provided
excellent weed control with minimal reduction to plant quality on Douglas fir.
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