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  • Author or Editor: Jason K. Norsworthy x
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Purple nutsedge (Cyperus rotundus) is a troublesome weed in vegetable crops in the southern United States. Methyl bromide is widely used for effective purple nutsedge control in polyethylene-mulched vegetable crops. With the impending ban on methyl bromide in the United States, an effective alternative is needed. Laboratory and greenhouse experiments were conducted to determine the effect of phenyl isothiocyanate (ITC) concentration and exposure period on purple nutsedge tuber viability and to compare the retention of phenyl ITC in soil under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Additionally, field experiments were conducted to evaluate the effectiveness of phenyl ITC under VIF mulch against purple nutsedge. A phenyl ITC concentration of 676 ppm in soil for 3 days in a sealed environment reduced purple nutsedge tuber viability by 97% compared with a nontreated control. Phenyl ITC retention was higher in soil covered with VIF mulch than with LDPE mulch. The predicted half-life of phenyl ITC under LDPE and VIF mulch was 6.1 and 8.9 days, respectively. In field experiments, phenyl ITC at 1500 kg·ha−1 under VIF mulch suppressed purple nutsedge shoots and reduced viable tuber density ≥72%, but control was not as effective as methyl bromide at 390 kg·ha−1 (67% methyl bromide:33% chloropicrin). Therefore, phenyl ITC up to 1500 kg·ha−1 under a VIF mulch is not a viable alternative to methyl bromide for effective purple nutsedge control.

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Field trials were conducted in 2006 and 2007 to evaluate the performance of ‘Caliente’ mustard cover crop and herbicide combinations for weed control in polyethylene-mulched bell pepper (Capsicum annuum). ‘Caliente’ mustard is a blend of brown mustard (Brassica juncea) and white mustard (Sinapis alba). Herbicide treatments included 1/2× and 1× rates of two pre-emergence (PRE) and two postdirected (PD) herbicides. PRE herbicides were applied 1 week before transplanting, whereas PD herbicides were applied at 4 to 5 weeks after transplanting. ‘Caliente’ mustard did not supplement weed control or improve bell pepper yield in herbicide-treated plots. There was a significant herbicide selection by application rate interaction for large crabgrass (Digitaria sanguinalis) control and bell pepper yield, but only the main effect of herbicide selection and application rate affected the control of purple nutsedge (Cyperus rotundus), yellow nutsedge (Cyperus esculentus), and palmer amaranth (Amaranthus palmeri). Bell pepper injury was not more than 9% from all herbicides and application rates. Except for large crabgrass, control of all weed species improved by increasing the application rate from 1/2× to 1×. S-metolachlor PRE provided more broad-spectrum weed control than other herbicides. Halosulfuron applied PRE or PD was selective to purple nutsedge and yellow nutsedge, whereas trifloxysulfuron performed better than halosulfuron on palmer amaranth and large crabgrass. Plots treated with the 1× rate of S-metolachlor or trifloxysulfuron produced the highest marketable bell pepper yield among the herbicide treatments, but no herbicide treatment allowed for marketable yield equivalent to the weed-free treatment.

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The phase-out of methyl bromide required an effective and economically viable alternative for weed management in polyethylene-mulched tomato (Solanum lycopersicum). A field experiment was conducted to compare economics of tomato production associated with crucifer (Brassicaceae) cover crops under low-density polyethylene mulch (LDPE) and virtually impermeable film (VIF) mulch with a standard treatment of methyl bromide:chloropicrin (67:33) at 350 lb/acre. Three crucifer cover crops, ‘Seventop’ turnip (Brassica rapa), ‘Pacific Gold’ oriental mustard (Brassica juncea), and Caliente [a blend of brown mustard (B. juncea) and white mustard (Sinapis alba)], were evaluated in combination with hand-weeding. Because of marginal weed control from crucifer cover crops, hand-weeding cost in all cover crop plots, regardless of mulch type, increased from $380.54/acre to $489.10/acre over that in methyl bromide plots. However, total weed management costs in the untreated control and cover crops with LDPE treatments were $17.82/acre to $111.33/acre lower than methyl bromide. Because of mulch expenses, VIF mulch increased the total weed management cost by $328.16/acre over LDPE mulch in the untreated control and cover crop treatments. Because of equivalent marketable yield, gross returns ($21,040.43/acre) were identical in all treatments. Preplant fumigation with methyl bromide provided $6260.90/acre of net returns in tomato production. The untreated control, ‘Seventop’ turnip, ‘Pacific Gold’ oriental mustard, and Caliente mustard under LDPE treatment were $54/acre, $54/acre, $98/acre, and $147/acre more profitable, respectively, than methyl bromide. However, in all other treatments under VIF, net returns relative to methyl bromide were reduced from $181/acre to $274/acre. Therefore, regardless of soil amendment with crucifer cover crops, hand-weeding can serve as an economically viable alternative to methyl bromide for weed control in LDPE-mulched tomato production, depending on the nature and level of pest infestation, labor availability, and wages.

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