Broccoli, cabbage, squash and watermelon response to halosulfuron preplant over plastic mulch

Nutsedge species are problematic in plastic-mulched vegetable production because of the weed's rapid reproduction and ability to penetrate the mulch. Vegetable growers rely heavily on halosulfuron to manage nutsedge species; however, the herbicide cannot be applied over mulch before vegetable transplanting due to potential crop injury. This can be problematic when multiple crops are produced on a single mulch installation. Field experiments were conducted to determine the response of broccoli, cabbage, squash, and watermelon to halosulfuron applied on top of mulch prior to transplanting. Halosulfuron at 80 g ai ha–¹ was applied 21, 14, 7, and 1 d before planting (DBP), and 160 g ai ha–¹ was applied 21 DBP. In all experiments, extending the interval between halosulfuron application and planting reduced crop injury. For squash and watermelon, visual injury, plant diameters/vine runner lengths, marketable fruit weights, and postharvest plant biomass resulted in similar values when applying 80 g ha–¹ 21 DBP and with the nontreated weed-free control. Reducing this interval increased injury for both crops. Visual crop injury and yield reductions up to 40% occurred, with halosulfuron applied 14, 7, or 1 DBP in squash and 1 DBP in watermelon. Broccoli and cabbage showed greater sensitivity, with injury and plant diameter reductions greater than 15%, even with halosulfuron applied at 80 g ha–¹ 21 DBP. Experimental results confirm that halosulfuron binds to plastic mulch, remains active, and is slowly released from the mulch over a substantial period, during rainfall or overhead irrigation events. Extending the plant-back interval to at least 21 d before transplanting did overcome squash and watermelon injury concerns with halosulfuron at 80 g ha–¹, but not broccoli and cabbage. Applying halosulfuron over mulch to control emerged nutsedge before planting squash and watermelon would be beneficial if adequate rainfall or irrigation and appropriate intervals between application and planting are implemented. Nomenclature: Halosulfuron; purple nutsedge, Cyperus rotundus L.; yellow nutsedge, Cyperus esculentus L.; broccoli, Brassica oleracea var. botrytis L. ‘Emerald crown'; cabbage, Brassica oleracea var. capitata L. ‘Cheers'; squash, Cucurbita pepo L. ‘Enterprise'; watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai ‘Sangria'