No abstract

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 (Pic) are the fumigants of choice for most growers using polyethylene mulch culture. In 1991, MBr was allegedly associated with stratospheric ozone depletion. 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 control 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 l01% 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 provided 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-l,3,5-thiadiazine-2-thione (dazomet); S-propyl butyl(ethyl)thiocarbamate (pebulate).

Yellow nutsedge, a weed commonly present in Florida vegetable fields, may substantially reduce crop yields when not controlled. Soil fumigation with methyl bromide effectively controls nutsedges, but methyl bromide is being phased out of production and use in the United States. Therefore, nutsedge management in bell pepper is a cause for concern. An experiment was conducted during four seasons (spring and fall of 1999 and 2000) to determine the tolerance of bell pepper grown at two in-row spacings (23 and 31 cm) to interference resulting from planted yellow nutsedge tuber densities (0 to 120 tubers/m2). Relative to yields with no nutsedge, pepper fruit yields in each season were reduced 10% with fewer than 5 planted tubers/m2. Yield losses increased more rapidly with an increase in initial nutsedge density from 0 to 30 than from 30 to 120 tubers/m2. With 30 nutsedge tubers/m2, large fruit yield was reduced 54 to 74% compared to that with no nutsedge. Nutsedge shoots overtopped the pepper plants as early as 6 wk after treatment when, with 15 planted tubers/m2, nutsedge interference reduced pepper plant biomass by 10 to 47%. In the absence of methyl bromide, weed control strategies with high efficacy against yellow nutsedge will be needed for bell pepper production.

Soil solarization is a process of soil disinfestation that involves solar heating of moist soil covered with transparent polyethylene film. This nonchemical approach to controlling soil-borne pests is being investigated as an alternative to methyl bromide fumigation. Summer solarization controlled annual weed species and suppressed purple nutsedge. Although some nutsedge tubers sprouted despite the solarization treatment, the resulting shoots were almost always trapped under the clear solarization film. Conversely, in rows that were mulched with black film, nutsedge rhizomes punctured the film so that leaf expansion occurred above the film. In controlled pot experiments conducted in darkness, yellow nutsedge rhizomes readily penetrated 19- and 30-μm clear films as effectively as opaque films. Thicker clear films and bubble film reduced nutsedge penetration. In the greenhouse and laboratory, nutsedge penetration of transparent polyethylene film was inversely related to irradiance levels when the film was in direct contact with the soil. However, when there was a 5- to 10-mm space between the soil and the film, the lowest irradiance level (30 μmol m−2s−1) was as effective as 320 μmol m−2s−1in reducing penetration by purple nutsedge. The film penetration by nutsedge rhizomes appears to be linked to a light-dependent morphological change from rhizome growth to leaf development, which occurs before film penetration with clear mulch and after film penetration with opaque mulch. The alternate sprouting and foliar scorching of nutsedge shoots trapped under clear films could potentially be exploited to deplete nutsedge tubers that occur at soil depths that do not develop lethal temperatures under soil solarization.