Herbicidal activity of three isothiocyanates against yellow nutsedge and their dissipation under two plastic mulches

• Three ITCs were tested for yellow nutsedge control and their retention under LDPE or VIF mulch.
• Methyl ITC was more effective than allyl ITC than phenyl ITC against yellow nutsedge.
• ITC retention was higher in soil covered with VIF mulch than with LDPE mulch.
• ITC retention differences were higher for phenyl ITC compared to allyl and methyl ITC.

Yellow nutsedge (Cyperus esculentus) is a major weed in polyethylene-mulched vegetable production. The phase out of methyl bromide in the U.S. requires an effective nutsedge management tool. Trial objectives were: 1) to evaluate the effect of phenyl, allyl, and methyl isothiocyanate (ITC) concentration and exposure period on yellow nutsedge tuber viability, tuber dry wt., and shoot emergence, and 2) to compare the dissipation of these three ITCs from treated soil under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. In greenhouse trial, methyl ITC was more effective than allyl ITC than phenyl ITC against yellow nutsedge tubers. The herbicidal activity of the all three ITCs against yellow nutsedge varied with their chemical structure (aliphatic ITC more effective than aromatic ITC) and molecular weight (efficacy increased with decreased molecular weight), concentration of ITC (effectiveness increased with increased concentration), and exposure period to target species (effectiveness increased with exposure time). In laboratory trial, ITCs dissipation was lower under VIF than LDPE mulch, with more differences for phenyl ITC compared to allyl and methyl ITC. Phenyl ITC half-life under LDPE and VIF mulch was 3.36 and 6.56 days, respectively. The corresponding values were 0.16 and 0.41 days for allyl ITC and 0.14 and 0.33 days for methyl ITC.