Methyl Bromide Alternatives for Vegetable Production In Georgia: On-Farm Trials

Three fumigant alternatives, methyl iodide plus chloropicirn (MIDAS), dimethyl disulfide plus chloropicrin (DMDS), and Telone II plus chloropicrin plus Vapam (3-Way) have exhibited promising results in small plot trials for the control of pests (weeds, pathogens, nematodes) in plasticulture production. The objective of this study was to determine if MIDAS, DMDS and the 3-Way are alternatives to methyl bromide (MB) with respect to weed control in large, on-farm pepper production trials. The study was conducted on three commercial farms located in Colquitt, Echols, and Tift Counties in GA during the spring of 2007. Treatments were replicated 4 times at each site. Plots ranged from 0.05 to 0.17 ha in size. Pepper height, pepper stand and weed emergence were evaluated throughout the season. Fruit were harvested according to grower practices and processed through commercial packing houses. Pepper stands and heights did not differ between treatments. Nutsedges and livid amaranth were the predominant weeds in the study. There were no differences in weed control among fumigant treatments at the Colquitt County farm; compared to a check plot, all fumigants reduced weed populations by 99%. Nutsedge and livid amaranth densities were significantly greater in the DMDS (18 to 85 plants/ha) treatment as compared to the MB (1 to 24 plants/ha) standard at the Echols County and Tift County sites. The MIDAS and 3-Way treatments did not differ from the MB standard with respect to weed control at both sites. Yield differences were only noted at the Tift County farm.  The mean number of boxes of Jumbo fruit produced (over 4 harvests) in the DMDS treatment was reduced, statistically, by 4% relative to the MB standard; the reduction in yield was attributed to weed competition. Although labeled for use on peppers in 47 states, the current price of MIDAS makes it cost prohibitive for GA growers. DMDS was registered for use in plasticulture production by the EPA in 2010. Efforts from this and other studies have shown that a DMDS system must include herbicides and must be applied under a high barrier mulch to provide weed control and yields similar to MB or the 3-Way.  The 3-way system has been the most readily adopted MB alternative in Georgia; in 2010, it was applied on over 70% of Georgia’s fumigated acreage.