Methyl bromide is a common fumigant for effective weed control in polyethylene-mulched vegetable crops. However, the ban on methyl bromide in the United States has created a need to find a suitable alternative. This study investigated the herbicidal efficacy of phenyl isothiocyanate (ITC) as a methyl bromide alternative for weed control in polyethylene-mulched bell pepper during 2006 and 2007. Six rates of phenyl ITC (0, 15, 75, 150, 750, 1,500 kg ha⁻¹) under low-density polyethylene (LDPE) or virtually impermeable film (VIF) mulch were tested against yellow nutsedge, Palmer amaranth, and large crabgrass. Additionally, a standard treatment of methyl bromide/chloropicrin (67 : 33%) at 390 kg ha⁻¹ under LDPE mulch was included for comparison. VIF mulch provided no advantage over LDPE mulch in either improving weed control or marketable yield in bell pepper. Unacceptable pepper injury (≥ 60%) occurred at the highest phenyl ITC rate of 1,500 kg ha⁻¹ at 2 WATP in both years, regardless of mulch type. Higher bell pepper injury was observed in 2006 (≥ 36%) than in 2007 (≤ 11%) at 750 kg ha⁻¹ of phenyl ITC. The lower injury in 2007 could be attributed to aeration of beds 48 h prior to transplanting. Regardless of mulch type, phenyl ITC at 2,071 (± 197) and 1,655 (± 309) kg ha⁻¹ was required to control yellow nutsedge, Palmer amaranth, and large crabgrass equivalent to methyl bromide in 2006 and 2007, respectively. Bell pepper marketable yield at all rates of phenyl ITC was lower than methyl bromide in 2006. In contrast, marketable yield in phenyl ITC at 750–kg ha⁻¹ was equivalent to methyl bromide in 2007. It is concluded that phenyl ITC should be applied at least 4.2 times higher rate than methyl bromide for effective weed control, and bed aeration is required to minimize crop injury and yield loss. Additional research is needed to test phenyl ITC in combination with other weed control strategies to obtain effective weed control with acceptable crop safety.

Nomenclature: Large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; yellow nutsedge, Cyperus esculentus L. CYPES; bell pepper, Capsicum annuum ‘Heritage'.

Methyl bromide es un fumigante común para el control efectivo de malezas en la producción de vegetales con coberturas plásticas. Sin embargo, la prohibición de este fumigante en los Estados Unidos ha creado la necesidad de encontrar una alternativa apropiada. Este estudio investigó la eficacia como herbicida de phenyl isothiocyanate (ITC) como alternativa a methyl bromide para el control de malezas en chile (pimiento) producido con cobertura de polyethylene durante 2006 y 2007. Seis dosis de phenyl ITC (0, 15, 75, 150, 750 y 1500 kg ha⁻¹) bajo una cobertura de polyethylene de baja densidad (LDPE) o de película virtualmente impermeable (VIF) fueron evaluadas contra Cyperus esculentus, Amaranthus palmeri y Digitaria sanguinalis. Adicionalmente, un tratamiento estándar de methyl bromide-chloropicrin (67:33) a 390 kg ha⁻¹ bajo cobertura de LDPE fue incluido con fines de comparación. La cobertura VIF no brindó ninguna ventaja sobre la cobertura LDPE para mejorar el control de malezas o el rendimiento del chile comercializable. Daños inaceptables causados al chile (≥60%) ocurrieron a la dosis más alta de phenyl ITC 1,500 kg ha⁻¹ a 2 semanas después del tratamiento en ambos años, sin importar el tipo de cobertura. En 2006, se observaron mayores daños en el chile (≥36%) que en 2007 (≤11%) a 750 kg ha⁻¹ de phenyl ITC