Abstract

Forest-tree nurseries in the United States have relied on methyl bromide (MBr) soil fumigation to control weeds, fungi, and nematodes. Due to the world-wide phase-out of MBr use, finding a soil fumigant alternative for MBr has been a priority for the forest nursery industry. A large-scale study comparing seven fumigants using operational application techniques and normal nursery management practices over three growing seasons was installed to determine the effects of MBr alternatives on seedling quality and quantity. Seedling densities at the end of the first growing season were similar across all soil fumigants tested. The newer chemistries, Pic+ and dimethyl-disulfide (DMDS), had seedlings with similar root collar diameters (RCDs) as MBr during the first and second growing seasons. Seedling RCDs declined for all treatments over the 3-year rotation due to the buildup of soilborne pests and weeds. Seedling root architecture and root morphology were similar for all soil fumigants. At the end of each growing season, nursery soils had similar levels of Trichoderma and nematode populations across all soil fumigants tested. These trials indicate that, while not the perfect replacement in all nursery soils, seedling production is still possible without MBr if compounds such as chloropicrin are used and managers pay close attention to weed and nematode pests that are less susceptible to chloropicrin than MBr.

Key words: Soil fumigation, chloropicrin, soilborne fungi, nematodes, Pinus taeda.