Effects of Application Method and Surfactants on Control of Yellow Nutsedge with Drip-Applied Herbicides in Polyethylene-Mulched Tomato
Type of Degreedissertation
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Use of polyethylene mulch in vegetable production provides many benefits including improved weed control; however, not all weed species are adequately controlled. Yellow nutsedge (Cyperus esculentus L.) can penetrate polyethylene mulch, degrading its durability, and is a serious concern for growers wanting to use the mulch for multicropping systems. To manage nutsedge species in these systems, halosulfuron (Sandea®) and S-metolachlor (Dual Magnum®) are often sprayed to beds prior to mulch application. However, application of herbicides through drip irrigation has become more prevalent and offers several benefits over sprayed applications. Research has shown the potential for use of drip-applied herbicides in commercial production; however, some issues need to be addressed. Recent research has indicated that yellow nutsedge control diminishes with increasing distance from drip emitters. Therefore, a need exists to improve the movement of drip-applied herbicides in polyethylene-mulched beds. Field studies were conducted to evaluate three selected application methods for improving movement of drip-applied halosulfuron, S-metolachlor, and fomesafen in polyethylene-mulched tomato. Treatments were evaluated based on their effect on yellow nutsedge punctures and the corresponding responses (plant height and yield) of a tomato (Solanum lycopersicum) crop. Drip-applied treatments were compared to a commercial standard, S-metolachlor, which was sprayed to the bed surface prior to mulch application. A nontreated control (beds with polyethylene mulch without herbicides) was included for comparison. The experiment was a factorial treatment arrangement of three drip application methods and three PRE-applied herbicides (halosulfuron at 54 g ai ha-1, S-metolachlor at 1.4 kg ha-1, and fomesafen at 280 g ha-1). Herbicides were applied either immediately following saturation of the planting beds (method A), along with an extended period used to saturate beds (method B), or just prior to bed saturation (method C). Results indicated that fomesafen applied with method B was the only treatment that provided a significant reduction in yellow nutsedge punctures (55% compared to commercial standard) while maintaining marketable yields comparable to the commercial standard. Furthermore, fomesafen and halosulfuron, each applied with method C, provided similar control of yellow nutsedge punctures and similar yields to the commercial standard. These results suggest, when applied with the appropriate method, drip-applied fomesafen and halosulfuron may provide suitable control of yellow nutsedge punctures in polyethylene-mulched tomato while maintaining desirable yields. Additional field studies were conducted to evaluate two nonionic surfactants, Integrate® 20 and Tween® 20, for improving movement of drip-applied halosulfuron, S-metolachlor, and fomesafen in polyethylene-mulched tomato. Treatments were again evaluated based on their effect on yellow nutsedge punctures and the corresponding responses of a tomato crop (plant height and yields). Drip-applied treatments were compared to a commercial standard of S-metolachlor which was sprayed to the bed surface prior to mulch application. A nontreated control (beds with polyethylene mulch without herbicides) was included for comparison. The experiment was a factorial treatment arrangement of three surfactant levels [Integrate® 20 at 2.8 kg ha-1, Tween® 20 at 2.8 kg ha-1 and no surfactant (i.e. none)] and three PRE-applied herbicides (halosulfuron at 54 g ai ha-1, S-metolachlor at 1.4 kg ha 1, and fomesafen at 280 g ha-1). Application of surfactants with drip-applied herbicides failed to reduce yellow nutsedge punctures relative to herbicides applied without surfactants. Results are likely due to the failure of surfactants to improve lateral movement of the herbicides underneath the polyethylene-mulched beds.