TECHNICAL NOTE Chloropicrin as a Soil Fumigation Treatment in Southern Pine Nurseries David B. South Because of concerns over the ozone layer, the annual amount of methyl bromide used for soil fumigation for crop production is decreasing. A promising alternative soil fumigation treatment involves applying 300 lb/ac of chloropicrin (CCl 3 NO 2 ) under a plastic tarp. Although this soil fumigant does not control weeds as well as an equivalent amount of methyl bromide, chloropicrin is an effective strategy for controlling many soilborne pests. The total amount of chloropicrin used for fumigation in southern pine nurseries will likely increase as use of methyl bromide fumigation declines. Keywords: pesticides, weeds, pathogens, nematodes, methyl bromide, nursery management N urseries in the southern United States produce approxi- mately 79% of the nation’s forest tree seedlings (Moulton and Hernandez 2000). In 2004, more than 1.1 billion seedlings were produced from southern nurseries (McNabb 2005). Most managers fumigate nursery soil to make efficient use of seed, to maintain a reputation for producing desirable planting stock, and to make profits. Fumigation reduces the number of pest problems, which aids in keeping production costs below $0.04 per pine seedling. For more than 50 years, nursery managers in the southern United States have used methyl bromide to fumigate soil prior to sowing (Henry 1953). However, ozone depletion in the stratosphere raised concerns over the production of synthetic chlorofluorocar- bons that could react chemically with ozone. As a result, a Vienna Convention (on the Protection of the Ozone Layer) determined that methyl bromide (a compound produced by oceans, forest fires, and ectomycorrhizae) should be listed as a Class 1 stratospheric ozone depletor. Under the Clean Air Act, it was decided that the produc- tion of synthetic methyl bromide was to be phased out by 2001. The Montreal Protocol was established in 1987, and an amendment to the protocol established a phase-out program by 2015 (or 2005 for developed countries). Because of the Montreal Protocol, finding alternative fumigation treatments has been a priority for the forest nursery industry. The Southern Forest Nursery Management Cooperative began to test alternative fumigation treatments in 1992 and tested 100% chloropicrin the same year (Table 1). Tests conducted with this fumigant have been promising. When used in conjunction with tarps and at a rate of 300 lb/ac, chloropicrin generally allows seed- ling production (i.e., the number of acceptable seedlings meeting a culling requirement per ft 2 ) generally comparable to that obtained from methyl bromide. In contrast, certain other legal alternative fumigants have (1) been unreliable; (2) stunted or killed adjacent seedlings; (3) produced variable seedlings; and (4) suppressed ben- eficial Trichoderma. This review article describes some of the oper- ational considerations managers should consider when fumigating with 100% chloropicrin. Use of a Tarp To obtain more consistent efficacy, a tarp is required when treat- ing with chloropicrin. The tarp can heat up the soil and can protect the soil from cold rains (which can delay the degradation of chlo- ropicrin). The tarp should be kept in place for at least 48 h, but it would be preferable to keep it in place for 5 days to maintain a longer treatment period and allow enough time for the chloropicrin to degrade. After 10 days under a tarp, there should be little chlorop- icrin remaining in the soil (Wang et al. 2006). In contrast, with daily sprinkler irrigation and no tarp, chloropicrin might still be detect- able on day 16 at depths below 1 ft (Wang et al. 2006). Some plastics are permeable, and 10 to 20% of the chloropicrin might be emitted into the atmosphere through permeable tarps (Wang et al. 2005). With a tarp in place for 7 days, treating with 300 lb/ac might reduce the population of nutsedge (Cyperus spp.) plants by 94%, but without a tarp, the reduction might be only 66% (Carey et al. 2004). At the Byromville Nursery, the use of a tarp greatly increased the soil concentration of chloropicrin in the upper foot of soil (Wang et al. 2006). For the above reasons, managers should consider using a tarp when applying chloropicrin. Rate In some nursery trials, chloropicrin rates as low as 125 lb/ac have been tested (Carey 1995a). However, this rate does not provide consistent results and is not as effective on weed seed as higher rates (Haar et al. 2003). In fact, reports from Florida indicate that low rates of chloropicrin can stimulate the emergence of nutsedge (Mo- tis and Gilreath 2002). For these reasons, mangers should consider applying 300 lb/ac of chloropicrin under a tarp (since higher rates will increase costs). After treatment, the soil should be allowed to aerate for 10 to 14 days. Received September 25, 2006; accepted October 13, 2006. David B. South (southdb@auburn.edu), School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL 36849-5418. Copyright © 2007 by the Society of American Foresters. SOUTH. J. APPL.FOR. 31(1) 2007 47 ABSTRACT Downloaded from https://academic.oup.com/sjaf/article/31/1/47/4782394 by guest on 28 November 2021