Solarization and chemical alternatives to methyl bromide for preplant soil treatment of strawberries

Solarization and chemical alternatives to methyl bromide (MeBr) soil fumigation for strawberry (Fragaria xananassa) were evaluated in a 3-year study in Savannah, Ga. Solarization using clear or black plastic, metam sodium (Sectagon), dazomet (Basamid), 1,3-dichloropropene and chloropicrin (Telone C-35), MeBr, and untreated control treatments were used. Solarization produced maximal soil temperatures of 55 to 60 degreesC (131 to 140 degreesF) at the 2.5 cm (I inch) depth, and 42 to 48 degreesC (108 to 118 degreesF) at the 15 cm (6 inch) depth. Clear and black plastic were generally equally effective in heating the soil. A double layer of clear plastic raised soil temperatures I to 2 degreesC (2 to 4 degreesF) above those under a single layer of clear at the 2.5 cm depth, although this occurred less frequently at the 15 cm depth. MeBr treatment increased yield by 46% and 128% in the first and second years, respectively, compared to the untreated control, but all treatments were similar in yield in year three. Season average fruit size differed among treatments in only the first year, with MeBr resulting in fruit 13% to 25% larger than other treatments. Yield for the metam sodium treatment in the first year was 34% lower than for MeBr, but comparable to MeBr in the other 2 years. Solarization treatment yields were similar to those of MeBr in the first and third years, but could not be analyzed in the second year due to plot damage. Dazomet treatment yields were similar to those of MeBr, metam sodium, and the untreated control in its single year of testing, but logistics of application and high costs may disfavor this treatment. The 1,3-dichloropropene/chloropicrin treatment performed as well as MeBr in its single year of testing. Three treatments-metain sodium, 1,3-dichloropropene/chloropicrin, and solarization with black plastic-offer viable, lower cost alternatives to MeBr.