Comparison of the Herbicidal Activity of Phenyl Isothiocyanate with Methyl Bromide in Polyethylene-Mulched Tomato

Abstract

Field experiments were conducted in 2006 and 2007 to evaluate the herbicidal activity of phenyl isothiocyanate (ITC) on yellow nutsedge, Palmer amaranth, and large crabgrass in tomato grown on two polyethylene-mulched types. Treatments included two mulch types (low density polyethylene [LDPE] mulch and virtually impermeable film [VIF] mulch) and phenyl ITC at 0, 15, 75, 150, 750, and 1,500 kg ha−1. A standard rate of methyl bromide/chloropicrin (67 : 33%) at 390 kg ha−1under LDPE mulch was included for comparison. Regardless of mulch type, phenyl ITC at 1,452 (±133) and 1,719 (±426) kg ha−1was required for broad-spectrum weed control equivalent to methyl bromide in 2006 and 2007, respectively. Tomato injury was ≥ 44% at the highest phenyl ITC rate of 1,500 kg ha−1at 2 wk after transplanting (WATP) both years, irrespective of mulch type. Greater crop injury was observed from 750 kg ha−1of phenyl ITC in 2006 (≥ 27%) than in 2007 (≤ 10%). The greater injury in 2006 was attributed to a higher phenyl ITC concentration because holes in the plastic mulch for transplanting were punched at the time of transplanting in 2006; whereas, in 2007 holes were punched 2 d before transplanting, allowing 2 d of aeration before transplanting. Tomato marketable yield at all rates of phenyl ITC was lower than with methyl bromide in 2006. However, in 2007, marketable yield in plots treated with phenyl ITC at 750 kg ha−1was equivalent to methyl bromide. Overall, VIF mulch was no more effective than LDPE mulch at increasing weed control or improving the marketable yield of tomato either year.