Purple nutsedge is a competitive and persistent perennial weed in the agronomic and horticultural cropping systems of the southeastern United States. Its management is a challenge during the growing season due to its ability to propagate vegetatively through underground rhizomes and tubers. Therefore, effective herbicide programs are needed that can check the spread of purple nutsedge and protect crop yields. Greenhouse experiments were conducted in 2024 to evaluate the response of purple nutsedge at two different growth stages (10 to 15 cm and 15 to 20 cm heights) to herbicides currently labeled for use in Mississippi cropping systems. Herbicides tested were glyphosate at 1,260 g ai ha–1, glufosinate at 672 g ai ha–1, bentazon at 1,680 g ai ha–1, halosulfuron at 69.5 g ai ha–1, and trifloxysulfuron at 6.9 g ai ha–1. Glyphosate was the most effective herbicide against purple nutsedge, providing >90% control, followed by halosulfuron, which provided 70% to 90% control at both growth stages. New shoot emergence was highest when glufosinate and bentazon were applied, and no new shoots emerged when glyphosate and halosulfuron were applied. More new shoots were observed when glufosinate and bentazon were applied when plants were 15 to 20 cm high compared to 10 to 15 cm. Shoot regrowth at 21 d after cutting the aboveground shoots indicated similar trends. A reduction of >90% in shoot and root biomass was observed when glyphosate, halosulfuron, and trifloxysulfuron were applied, whereas glufosinate and bentazon applications resulted in 50% less biomass reduction. Overall, herbicide efficacy against purple nutsedge was greater when plants were treated at the recommended height of 10 to 15 cm rather than 15 to 20 cm. The study results indicated that both herbicide mode of action and application timing are important for better purple nutsedge management in cropping systems.

Sulfuryl fluoride (SF) is currently used as a fumigant for control of drywood termites and insects in building structures, vehicles, wood products, postharvest commodities, and food processing facilities. This research investigated the feasibility of using SF as a preplant soil fumigant for purple nutsedge control in plastic-mulched tomato production. SF treatments included SF injected through drip tapes or SF injected through drip tapes a few hours following shank injection of chloropicrin (Pic). Results revealed that SF alone at 224, 336, or 448 kg ha−1 was generally less effective compared with when it was applied in conjunction with Pic at 168 kg ha−1. SF alone provided inconsistent control of purple nutsedge. In contrast, SF + Pic was as efficacious or more efficacious on purple nutsedge than the industry standards, including 1,3-dichloropropene (1,3-D) plus Pic and metam potassium. None of the fumigant treatments visually injured tomato plants, stunted growth, or adversely affected tomato yield. In one of the four tomato seasons, tomato plants growing in plots fumigated with SF + Pic resulted in taller tomato plants and higher markable yields. Results indicate that soil fumigation with SF + Pic is safe on plastic-mulched tomato and effectively controls purple nutsedge.

Metam potassium (metam-K) is a soil fumigant used commonly in Florida at the end of the tomato and pepper production season. The fumigant essentially cleans a field by killing the established weeds and crops after harvest. The goal of this project was to determine the optimal rate of metam-K for the effective termination of tomato, pepper, and established weeds such as purple nutsedge, goosegrass, and dogfennel. Tomato, pepper, and purple nutsedge at bed center were effectively terminated with the metam-K rate of 65 kg ha−1. Optimal rates required for the termination of goosegrass and dogfennel were 91 and 156 kg ha−1, respectively. In contrast, metam-K at 500 to 680 kg ha−1 was required to terminate purple nutsedge on bed edges. The reduced efficacy of metam-K at bed edge might be related to the limited movement of metam-K in soil.

Greenhouse experiments were conducted to determine the extent of purple nutsedge tuber depletion and shoot regrowth when shoots were removed periodically from plants sprouting from tubers of different original weights. Presprouted purple nutsedge tubers were planted in 0.5-L plastic containers filled with potting medium. Tuber weight categories were 0.25, 0.50, 0.75, and 1 g per tuber. Shoots were removed by cutting at soil level beginning 6, 12, 18, 24, or 30 d after transplanting (DAT). Shoot removal occurred every 6 d after the first removal with a minimum of seven removals. Tuber weight had an effect on both shoot number and dry weight when the first removal was imposed either 6 or 12 DAT. When initial shoot removal was begun 6 DAT, total tuber depletion was achieved after the fifth removal for tubers weighing 0.25 g and after the seventh removal for tubers weighing 0.50 g. When the initial removal was delayed until 12 DAT, only tubers weighing 0.25 g were depleted after the sixth removal. No tuber depletion occurred for tubers weighing 0.75 g or more at any initial removal time. Greater initial sprouting vigor was observed among large tubers compared to smaller ones. Early removal (6 DAT) promoted the formation of more shoots from tubers weighing 0.75 or 1 g.

An isolate of the fungus Dactylaria higginsii obtained from purple nutsedge in Florida was highly pathogenic to Cyperus spp. The potential of this isolate as a bioherbicide was field tested in natural populations of purple nutsedge in Gainesville and Jay, FL. The fungus was applied in 0.5% Metamucil® as a carrier, and the treatments were: carrier only, 105 conidia/ml + carrier, and 106 conidia/ml + carrier. Treatments were applied as single, double, or triple postemergence (POST) sprays at biweekly intervals. The disease and secondary infections developed in about 5 and 15 d after inoculation, respectively, killing most of the infected leaves. All weed growth parameters and disease progress rates were affected by inoculum dosage and inoculation frequencies. Three inoculations, each at 106 conidia/ml, provided effective control of purple nutsedge compared to a single inoculation, as measured by shoot dry weight, tuber numbers, and tuber dry weight. Higher rates of disease progress and disease levels, defined by the area under the disease progress curve (AUDPC), occurred with three inoculations at 106 conidia/ml. Disease progress was slower and the level of weed control was lower at 105 conidia/ml compared to the higher inoculum level. Three applications of 106 conidia/ml provided >90% nutsedge control. Dactylaria higginsii appears to be an effective bioherbicide candidate deserving further development for commercial use.