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Matthew A. Cutulle, Howard F. Harrison Jr., Chandresakar S. Kousik, Phillip A. Wadl, and Amnon Levi

herbicide clomazone ( Anonymous, 2005 ) is widely used in cucurbit crop production in the United States. Clomazone controls many important annual weeds such as barnyardgrass [ Echinochloa crus-galli (L.) Beauv], velvetleaf ( Abutilon theophrasti Medicus

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

Watermelon is grown on over 60,000 ha in the United States and is an important crop in many states. The herbicide clomazone ( Anonymous, 2005 ) is widely used in watermelon production in the United States, except California. It controls many

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Howard F. Harrison Jr. and Mark W. Farnham

differences in weed species common in the regions and higher rainfall in the east that increases weed growth and stimulates frequent weed seed germination. Clomazone is registered for weed management in direct seeded and transplanted cabbage production in the

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Wayne C. Porter

Clomazone was evaluated for reemergence weed control in summer squash, watermelon, cantaloupe, cucumber, and pumpkin. Clomazone was applied preplant incorporated or surface-applied after planting. All crops exhibited varying degrees of chlorosis in the cotyledonary stage and first one to three true leaves. Cucurbit tolerance to clomazone was pumpkin = squash > cucumber > watermelon > cantaloupe. Method of application did not affect crop vigor. Some pumpkin cultivars were more tolerant than others. Clomazone controlled Brachiaria platyphylla and Portulaca oleracea with both methods of application. Surface application provided better control of Amaranthus hybridus and A. spinosa. Mollugo verticillata was not controlled. Preplant incorporated application of clomazone tended to reduce the yield of watermelon.

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H. E. Hohlt, H. P. Wilson, and T. E. Hines

During 1989, clomazone (Command) was applied pretransplant or preemergence to transplanted and seeded watermelon (Citrullus lanatus, cv. Charleston Gray), respectively. Rates of 280, 414, and 560 g ai·ha-1 (0.50, 0.75, 1.0 pt/A) clomazone were applied to a Bojac sandy loam. Plots were rated for percentage weed control 21 DAT. Control of common lambsquarters [Chenopodium album (L.)], large crabgrass [Digitaria sanguinalis (L.) Scop.], and smooth pigweed (Amaranthus hybridus L.) increased with rate although smooth pigweed control was low. A significant phytotoxic injury characterized by bleaching and reduced growth occurred at all rates on melon transplants. No significant phytotoxicity occurred in seeded plots 35 DAT. Vine length (cm) was recorded 42 DAT. Vine length was reduced significantly at the 560 g·ha-1 rate in transplants. Vine length of seeded watermelons was not significantly affected.

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Carla D. White and L. Weston

The purpose of this experiment was to determine if differential tolerance levels of velvetleaf (Abutilon theophrasti), jimsonweed (Datura stramonium) and morningglory (Ipomea hederacea) to 14C clomazone, a preemergence herbicide, was due to uptake, translocation and metabolism of clomazone. The plant species were placed in a clomazone Hoagland solution for 48 and 96 hours. Afterwards, extraction of chlorophyll, oxidation of plant material, and liquid scintillation spectroscopy procedures were used to determine if the differences existed. Morningglory were found to have a higher rate of metabolism and was the most tolerant to clomazone. It is hypothesized that these results are due to Morningglory's larger size and tendency to retain clomazone in the roots.

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Carla D. White and L. Weston

The purpose of this experiment was to determine if differential tolerance levels of velvetleaf (Abutilon theophrasti), jimsonweed (Datura stramonium) and morningglory (Ipomea hederacea) to 14C clomazone, a preemergence herbicide, was due to uptake, translocation and metabolism of clomazone. The plant species were placed in a clomazone Hoagland solution for 48 and 96 hours. Afterwards, extraction of chlorophyll, oxidation of plant material, and liquid scintillation spectroscopy procedures were used to determine if the differences existed. Morningglory were found to have a higher rate of metabolism and was the most tolerant to clomazone. It is hypothesized that these results are due to Morningglory's larger size and tendency to retain clomazone in the roots.

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Bernard H. Zandstra, Sylvia Morse, Rodney V. Tocco, and Jarrod J. Morrice

each other ( P ≤ 0.05). The 1.2-lb/acre terbacil treatment consistently provided the best overall weed control ( Fig. 1 ) for quackgrass, spotted knapweed, and wild carrot. Clomazone at 1 lb/acre suppressed quackgrass and spotted knapweed but did not

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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 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).