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Timothy L. Grey, David C. Bridges, and D. Scott NeSmith

Field studies were conducted to evaluate the tolerance of several pepper (Capsicum annuum L.) cultivars to the herbicide clomazone. Peppers tested included the bell cultivars Yolo Wonder and Jupiter; the banana cultivar Sweet Banana; and the pungent cultivars Jalapeno and Red Chili. Treatments were clomazone at 0.56 or 1.12 kg·ha-1 a.i. applied either preplant incorporated (PPI), pretransplant (PRE-T), or posttransplant (POS-T) on the day of transplanting, plus a nontreated control. Clomazone at 1.12 kg·ha-1 a.i. PPI and PRE-T significantly injured (bleaching or chlorosis of foliage) `Sweet Banana' (40% and 20%, respectively) and `Red Chili' (30% and 18%, respectively) in 1993 in early-season evaluations, but this injury was transient and did not significantly affect total fruit number or yield. Injury to any cultivar from POS-T clomazone at 0.56 and 1.12 kg·ha-1 a.i. was nonsignificant. Overall, tolerance to clomazone was excellent for all treatments and across all cultivars. Yield was not reduced significantly by any treatment. Chemical names used: 2-[(2-chlorophenyl) methyl]-4, 4-dimethyl-3-isoxazolidinone (clomazone).

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Timothy L. Grey, David C. Bridges, and D. Scott NeSmith

Field studies were conducted in 1993, 1994, and 1995 to determine tolerance of seeded and transplanted watermelon [Citrullus lanatus (Thunb.) Matsum and Nak.] to clomazone, ethalfluralin, and pendimethalin using method of stand establishment (directseeded vs. transplanted) and time of herbicide application [preplant soil incorporated (PPI), preplant to the surface (PP), or postplant to the surface (POP)] as variables. Yield and average fruit weight in plots with clomazone were equal to or greater than those in control plots for the 3-year study regardless of method of application. Bleaching and stunting were evident with clomazone in early-season ratings, but injury was transient and did not affect quality or yield. Of the three herbicides, ethalfluralin PPI resulted in the greatest injury, stand reduction, and yield reduction of the three herbicides. Pendimethalin (PPI, PP, or POP) reduced yield of direct-seeded but not of transplanted watermelon. Chemical names used: 2-[(-2-chlorophenyl)methyl]-4, 4-dimethyl-3-isoxazolidinone (clomazone); N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl) benzenamine (ethalfluralin); N-(1-ethylopropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).

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Howard F. Harrison Jr., Chandrasekar S. Kousik, and Amnon Levi

Clomazone herbicide is registered for use in watermelon; however, crop tolerance is marginal, and the recommended use rates (0.17 to 0.28 kg a.i./ha) are lower for watermelon than for other crops. In a greenhouse germplasm evaluation experiment including 56 germplasm accessions and watermelon cultivars, three Citrullus lanatus var. citroides PI accessions (PI 482324, PI 5003540, and PI 532624) were not injured by clomazone, whereas most of the other accessions and cultivars were moderately or severely injured. A greenhouse concentration response experiment demonstrated that the clomazone concentration required to cause moderate injury to the tolerant ‘PI 500354’ was approximately three times the concentration required to cause similar injury to the susceptible citroides accession ‘PI 244017’, and the concentration required to cause 50% shoot biomass reduction was approximately five times greater for ‘PI 500354’ than for ‘Charleston Gray’ watermelon. Subsequent field experiments demonstrated that two tolerant accessions (‘PI 500354’ and ‘PI 482324’) were injured less initially by clomazone and recovered more rapidly from clomazone injury than two susceptible accessions (‘PI 244017’ and ‘PI 271773’) and two watermelon cultivars (‘Charleston Gray’ and ‘Crimson Sweet’). Tolerant germplasm accessions like ‘PI 482324’ and ‘PI 500354’ may be useful as sources of clomazone tolerance in watermelon breeding. Chemical name used: clomazone {2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone}.

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Timothy L. Grey, David C. Bridges, and D. Scott NeSmith

Field studies were conducted in 1993, 1994, and 1996 to determine the tolerance of several cultivars of zucchini and yellow crookneck squash (Cucurbita pepo L.) to various rates and methods of application of clomazone, ethalfluralin, and pendimethalin. Applying herbicides preplant soil incorporated (PPI), preemergence (PRE), at seedling emergence (SE), or early postemergence (EPOT) resulted in plant injury that varied from 0% to 98%. Ethalfluralin and pendimethalin (PPI) at 1.12 kg·ha–1 a.i. resulted in the greatest stand and yield reductions across all cultivars. Fruit number and weight declined for all cultivars in 1993 and 1994 as the amount of pendimethalin applied PRE was increased. Zucchini (`Senator') fruit size was significantly reduced for the first three harvests in 1993 by PRE application of pendimethalin or PPI application of ethalfluralin, at all rates. Yellow squash (`Dixie') fruit size was unaffected by herbicide treatment for any harvests during 1993 or 1996. Yellow and zucchini squash yield, fruit number, and average fruit weight were equal to, or greater than, those of the untreated control for PRE clomazone using either the emulsifiable concentrate formulation (EC) during 1993, 1994, and 1996 or the microencapsulated formulation (ME) during 1996. Foliar bleaching and stunting by clomazone was evident in early-season visual observations and ratings, but the effect was transient. Foliar bleaching by clomazone PPI (1.12 kg·ha–1 a.i.) was more evident in `Senator' zucchini, and yield was significantly reduced in 1993. These effects of clomazone PPI were not evident in 1994 for either `Elite' or `Senator' zucchini squash. Chemical names used: 2-[(2-chlorophenyl)methyl]-4, 4-dimethyl-3-isoxazolidinone (clomazone); N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl) benzenamine (ethalfluralin); N-(1-ethylopropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).

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E. Ryan Harrelson, Greg D. Hoyt, John L. Havlin, and David W. Monks

] and clomazone [2-(2-chlorophenyl) methyl-4, 4-dimethyl-3-isoxazolidinone] herbicide at 4.6 L·ha −1 to control weeds. Esfenvalerate [(s)-cyano (3-phenoxyphenyl) methyl (s)-4-chloro-alpha- (1-methylethyl) benzeneacetate] at 0.43 L·ha −1 was applied

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E. Ryan Harrelson, Greg D. Hoyt, John L. Havlin, and David W. Monks

nitrate (100 kg·ha −1 N) was surface band-applied 15 cm beside the row 2 weeks after planting. A single application of ethalfluralin [n-ethyl-N-(2methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl benzeneamine)] and clomazone [2-(2-chlorophenyl) methyl-4