Fumigant alternatives to methyl bromide for polyethylene-mulched tomato

Tomato (Lycopersicon esculentum Mill.) was grown to evaluate various chemicals as possible alternatives to methyl bromide soil fumigation. Due to a combination of weeds, nematodes, and soil fungi, the use of a broad-spectrum fumigant has been essential for economical tomato production in Florida. Methyl bromide (MBr) and combinations of MBr with chloropicrin (Pie) are the fumigants of choice: for most growers using polyethylene mulch culture. In 1991, MBr was allegedly associated with stratospheric azone depiction. The U.S. Environmental Protection Agency has since mandated a phaseout of MBr for soil fumigation in the United States by the year 2001. At three locations in Florida, alternative soil fumigants were evaluated, including soil injected 98% MBr-2% Pic at 450 kg.ha(-1), 67% MBr-33% Pic (390 kg.ha(-1)), Pic (390 kg.ha(-1)), dichloropropene + 17% Pic (1,3-D + Pic) at 327 L.ha(-1), and metam-sodium (935 L.ha(-1)). Also, metam-sodium and tetrathiocarbonate (1870 L.ha(-1)) were applied by drip irrigation. Dazomet (450 kg.ha(-1)) was surface applied and soil incorporated. Pebulate (4.5 kg.ha(-1)) was soil incorporated with some treatments. Pic and 1,3-D + Pic treatments provided good to moderate control of nematodes and soil fungi except in one of the six studies, in which nematode central with 1,3-D was moderate to poor. Nutsedge densities were suppressed by addition of pebulate. Tomato fruit yields with 1,3-D + Pic + pebulate and with Pic + pebulate at the three sites ranged from 85% to 114%, 60% to 95%, and 101% to 119%, respectively, of that obtained with MBr treatments. Pest control and crop yield were lower with treatments other than the above pebulate-containing or MBr-containing treatments. These studies indicate that no one alternative pesticide can provide the consistent broad-spectrum control presided by MBr. Chemical names used: trichloronitromethane (chloropicrin); 1,3-dichloropropene (1,3-D); sodium N-methyldithiocarbamate (metam-sodium); sodium tetrathiocarbonate (tetrathiocarbonate); 3,5-dimethyl-(2H)-tetrahydro-1,3,5-thiadiazine-2-thione (dazomet);S-propyl butyl(ethyl)thiocarbamate (pebulate).