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

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TOLERANCES OF ORNAMENTAL SHRUBS TO HALOSULFURON,
SULFENTRAZONE AND V-10142. T.L. Mervosh and J.F. Ahrens, Connecticut
Agricultural Experiment Station, Windsor.
ABSTRACT
We conducted research as part of the IR-4 Ornamental Horticulture Program to
evaluate herbicide tolerances of four woody ornamental plants. The shrubs were
planted in 1-gallon containers (6-in diameter) on May 1, 2006. Plants were ‘Emerald
Green’ arborvitae (Thuja occidentalis ‘Smargd’), ‘P.J.M.’ rhododendron (Rhododendron
‘P.J.M.’), bridal-wreath spiraea (Spiraea x bumalda ‘Goldflame’) and dwarf burning-bush
(Euonymus alatus ‘Compactus’). Each plot contained three plants of each species.
Treatments, including an untreated check, were replicated four times in a randomized
complete block design. Herbicide treatments were applied over the top of plants at
normal (1X), twice normal (2X) and four times normal (4X) dosages on May 4 and again
on July 7, 2006. Treatments consisted of sulfentrazone 0.2G (0.125, 0.25 and 0.5 lb
ai/A), sulfentrazone 4F (0.125, 0.25 and 0.5 lb ai/A) and V-10142 75WG (0.5, 1.0 and
2.0 lb ai/A). Halosulfuron 75DF treatments (0.047, 0.094 and 0.188 lb ai/A) were
applied over Spiraea spp. only.
Herbicide sprays were applied in a volume of 30 gal/A using a CO 2 -pressurized
sprayer with two 8003VS nozzle tips. Treatments were sprayed over the top of prewetted
plants. Ten minutes later, plants were watered by overhead irrigation for 20 min.
After foliage had dried, granular treatments were applied. Sulfentrazone 0.2G granules
(amount per 10 ft 2 ) and sieved sand of like size were mixed in a shaker jar and applied
uniformly over a plot of plants within a 10-ft 2 frame. Irrigation followed for 20 min.
Evaluations of plant injury (0 = no injury; 10 = dead) or plant vigor (10 = most
vigorous; 0 = dead) were recorded several times after each treatment application.
Halosulfuron at all doses caused severe stunting and chlorosis of Spiraea spp. Some
recovery occurred late in the season for Spiraea treated with the 1X dose of halosulfuron,
but plant vigor (< 7.3) was still not acceptable. The first application of sulfentrazone 0.2G
treatments injured Spiraea only (injury ratings of 1.2 to 2.7). However, Spiraea vigor was
excellent at 9 weeks after the first treatment (9 WAT-1), and injury was insignificant
following the second application of sulfentrazone 0.2G. The first application of
sulfentrazone 4F treatments caused initial injury to Spiraea (2.5 to 5.5), rhododendron
(1.3 to 2.0) and burning-bush (0.8 to 2.8). By 9 WAT-1, plant vigor was excellent (>9)
except for Spiraea treated with sulfentrazone 4F at 2X and 4X doses (vigor of 8.9 and 7.3,
respectively). Spiraea was the only species injured by the second application of
sulfentrazone 4F. At 4 WAT-1 following V-10142 treatments, severe injury occurred on
Spiraea (7.6 to 8.3) and burning-bush (5.1 to 7.6), and lesser injury on Arborvitae spp.
(1.3 to 3.3) and Rhododendron (0.7 to 2.3). The second application of V-10142 caused
additional injury to all plants. By the final evaluation on October 4 (12 WAT-2), plant vigor
ratings were lowest for Spiraea (1.3 to 0.2) and highest for arborvitae (9.6 to 6.9).
No weeds were present in containers on the herbicide application dates.
Herbicidal efficacy of halosulfuron was not evaluated. Neither sulfentrazone nor V-
10142 treatments were effective at preventing horseweed (Conyza canadensis).
Sulfentrazone treatments did not prevent smallflowered bittercress (Cardamine
parviflora) or northern willowherb (Epilobium ciliatum).
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