Purple nutsedge management in tomato plasticulture: A study on the effectiveness of preemergence herbicide S-metolachlor and its co-application with fertilizer enhancer and chelated iron

Purple nutsedge (Cyperus rotundus L.) poses a significant challenge to Florida tomato (Solanum lycopersicum L.) producers due to its ability to puncture plastic mulch, resilient tubers, and rapid rhizome proliferation. Preemergence herbicides effectively suppress purple nutsedge in tomatoes under plastic mulch. Although the impact of co-application of herbicides with fertilizers has been studied in row crops, its potential in vegetable plasticulture systems remains unexplored. This study aimed to evaluate the effectiveness and crop safety of the preemergence herbicide S-metolachlor, both as a standalone treatment and in combination with a fertilizer enhancer or chelated iron in tomato plasticulture. Field trials at the University of Florida's Southwest Florida Research and Education Center, Immokalee, FL, involved applying S-metolachlor at the recommended rate of 1 kg a.i. ha⁻¹ on raised beds before installing plastic mulch. The herbicide was applied as a blanket spray alone, mixed with fertilizer enhancer, and coated on chelated iron fertilizer. Results indicate that using S-metolachlor alone effectively reduced purple nutsedge density compared to the nontreated control in both trials I and II. Combining S-metolachlor with fertilizer enhancer or chelated iron resulted in a >30% and 57% reduction in purple nutsedge density, respectively, compared to the nontreated control in trial II. These treatments did not adversely impact chlorophyll content or crop yield (p > 0.05) compared to the nontreated control. Notably, tomato yield significantly (p < 0.05) decreased with increased purple nutsedge density at 4, 8, and 12 weeks after transplanting. Overall, the results from both trials suggest that using S-metolachlor is an effective approach to reduce purple nutsedge infestation in plastic-mulched raised beds without negatively impacting tomato health and productivity.