Selectivity of fomesafen based systems for preemergence weed control in cucurbit crops

Experiments at two sites during two years evaluated the selectivity of preemergence fomesafen in cucurbit crops of winter and summer squash, zucchini, cantaloupe, cucumber, and pumpkin. Cucumbers were the most sensitive of the cucurbit crops to fomesafen and produced little or no fruit in two out of three experiments when applied at 0.28 kg ai ha⁻¹. Fomesafen also reduced cantaloupe yield. Visual damage was noted on the other crops tested, but crop yield was not impacted by fomesafen at 0.28–0.35 kg ai ha⁻¹. With the exception of cucumbers, injury caused by fomesafen to cucurbit crops was transitory even when fomesafen-treated soil splashed onto the leaves of emerging cucurbits during a powerful thunderstorm at one of the test sites. Control of redroot pigweed (Amaranthus retroflexus), Powell amaranth (Amaranthus powellii) and other Amaranthus spp., lambsquarters (Chenopodium album), hairy nightshade (Solanum physafolium), common purslane (Portulaca oleraceae), and velvetleaf (Abutilon theophrastii) ranged from 92 to 100% with fomesafen applied at 0.28 kg ai ha⁻¹. The excellent efficacy on these difficult to control weed species suggests that lower rates of fomesafen may be appropriate and improve crop tolerance, particularly if fomesafen is tankmix-applied with other preemergence herbicides such as s-metolachlor or dimethenamid-p. Weed control with these combinations was excellent for all weed species in these experiments.