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In Florida, nutsedge (Cyperus spp.) is a major weed problem in mulched-vegetable production. As methyl bromide (MBr) is phased out, alternatives are essential for growers. However, because of critical use exemptions, growers will still be able to use restricted amounts of MBr. Therefore, using highly-retentive mulch, such as virtually impermeable film (VIF), can reduce fumigant loss and may allow rate reduction without compromising efficacy. Preliminary studies have shown that metalized mulches can be an alternative to VIF. However, further studies are needed to compare MBr retention properties and nutsedge control of high density polyethylene (HDPE) mulch, VIF, and metalized mulch. Two field studies were conducted in spring 2005, in Ruskin, Florida. Metalized and HDPE mulches, and VIF were combined with the following rates of MBr + chloropicrin (Pic) (67/33, w/w): 175 and 350 lb/acre. Methyl bromide retention was evaluated in soil air samples at 1, 2, 4, and 6 days after treatment (DAT). Nutsedge plants were counted at 2, 4, 7, 9, and 12 weeks after treatment (WAT). Data were examined with regression analysis to establish the relationship between the time and both MBr concentration and nutsedge densities. Concentration of MBr + Pic under either the metalized mulch or VIF was about 6 times higher than under HDPE at 5 DAT, regardless of the MBr + Pic rate. At 12 WAT, nutsedge population was <1 plant/50 ft row with metalized and VIF and 175 lb/acre of MBr + Pic, whereas about 25 plants/50 ft row were present with 350 lb/acre of the fumigant and HPDE. The weed population reached >100 plants/50 ft row with 175 lb/acre of MBr + Pic. These findings demonstrate that metalized and VIF mulches can provide effective control of nutsedge with one-half of the commercially used MBr + Pic rate.

Previous research has demonstrated stimulation of purple and yellow nutsedge (Cyperus rotundus and C. esculentus) with chloropicrin when applied at rates ranging from 100 to 150 lbs/acre (112 to 168 kg·ha^–1) under low or high density polyethylene film mulch. This stimulatory effect has been exploited in research by developing a program of metam application 5 days after application of chloropicrin, thus placing metam in the soil once the tubers have begun to sprout and are most vulnerable. This project was expanded in 2004–05 to include the commercial emulsifiable concentrate formulation of 65% 1,3-dichloropropene and 35% chloropicrin (1,3-D + Pic) and virtually impermeable film mulch as well as high density polyethylene film. The test site was a commercial tomato farm in west central Florida with a heavy infestation of purple nutsedge. Chloropicrin was applied into raised beds through three gas knives, while 1,3-D + Pic and metam potassium were applied in 1 acre inch of water through 2 drip irrigation tubes spaced 10 inches apart and 5 inches from the bed center. Metam was applied 5 days after application of chloropicrin and 1,3-D + Pic. Treatments were applied under both standard high density polyethylene film (Hilex and Bromostop) VIF. Stimulation of nutsedge sprouting and emergence was about the same with either chloropicrin alone or combined with 1,3-D; however, there was some enhancement when applied under VIF. There was a slight improvement in efficacy of metam potassium when applied alone under VIF, contrary to previous results. Application of metam 5 days after application of chloropicrin or 1,3-D + Pic greatly improved nutsedge control over that observed without the subsequent application of metam and VIF improved results to some degree. Producers of drip irrigated crops in Florida can achieve acceptable to excellent nutsedge control using this sequential application technique combined with VIF; however, the addition of a second drip tube on the bed top increases expense by about $125/acre and is not compatible with crops grown with more than a single row on the bed.

Field trials were conducted in Bradenton, Fla., to determine the effect of purple and yellow nutsedge (Cyperus rotundus and C. esculentum) time of emergence on the area of influence of each weed on bell pepper (Capsicum annuum). Each weed-bell pepper complex was studied separately. A single weed was transplanted 1, 2, 3, 4, and 5 weeks after bell pepper transplanting (WAT) and bell pepper yield was collected at 0, 30, 60, and 90 cm from each weed. Bell pepper yield data indicated that yellow nutsedge was more aggressive than purple nutsedge interfering with bell pepper. When yellow nutsedge emerged 1 WAT, bell pepper yield losses were between 32 and 57% for plants at 0 and 30 cm away from the weed, respectively, which represents at least a density of approximately 3.5 plants/m². For purple nutsedge, one weed growing since 1 WAT between two bell pepper plants (0 cm; 10 plants/m²) produced a yield reduction of 31%. These results indicated that low nutsedge densities, which are commonly believed to be unimportant, can cause significant bell pepper yield reductions.