Alternatives to methyl bromide soil fumigation for vegetable and floriculture production
Location: Subtropical Plant Pathology Research
Title: Performance of methyl bromide alternatives for weed control
Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 11, 2011
Publication Date: February 7, 2009
Citation: Rosskopf, E.N., Burelle, N.K., Iriarte, F.B., Butler, D.M., Muramoto, J. 2009. Performance of methyl bromide alternatives for weed control. Weed Science Society of America Meeting Abstracts.
Numerous research trials were conducted over five years to evaluate potential alternatives to methyl bromide for control of a broad spectrum of soilborne pests, including nematodes, plant pathogenic fungi, and weeds. Trials were conducted at the field demonstration, experimental plot, greenhouse, and laboratory scales, depending on the registration and/or developmental status of the compounds or techniques tested. Chemical materials tested include methyl iodide:chloropicrin (MeI) and dimethyl disulfide:chloropicrin (DMDS) combinations. Methyl iodide is registered for use in Florida under the trade name Midas and there is a current experimental use permit for dimethyl disulfide under the name Paladin. Weed control with both materials was comparable to methyl bromide in raised-bed production of tomatoes and flat fumigation floriculture production of celosia, caladium, and delphinium. In one flat fumigation trial on sunflower, weed control with 701 L/ha of DMDS under low density polyethylene was lower than with 468 L/ha under metalized film and methyl bromide. Generally, weed control with these fumigants was statistically equivalent to methyl bromide, although somewhat higher numerically with DMDS. In raised bed trials in a tomato-melon double crop, the combination of halosulfuron-methyl, metolachlor, and rimsulfuron provided weed control during the tomato crop that was equivalent to methyl bromide, although the control was not equivalent by the end of the melon crop. Other chemicals tested include ethanedinitrile, and a novel combination of organic compounds referred to as SPK. SPK has been tested in laboratory, greenhouse, and microplot trials and has broad-spectrum activity. In greenhouse and microplot trials, yellow and purple nutsedge (Cyperus esculentus and C. rotundus), goosegrass (Eleusine indica), crabgrass (Digitaria sanguinalis), smooth pigweed (Amaranthus hybridus), and sicklepod (Senna obtusifolia) were controlled with a solution containing as little as 2.25% of the active ingredient. The level of control achieved was equivalent to a weed-free check. This material is also an excellent nematicide and broad-spectrum fungicide. Ethanedinitrile has been tested in laboratory assays only. Yellow nutsedge tuber germination was reduced to 10% with a concentration of 20 mg/L and was completely eliminated with 50 mg/L. Germination of common purslane (Portulaca oleraceae) seeds was also reduced to 0% with the 20 mg/L treatment. Sicklepod seeds were more resistant to the treatment and 100 mg/L was required to reduce germination below 10%. Non-chemical alternatives that are being investigated include soil solarization, the combination of paper mulch and plastic mulch, and anaerobic soil disinfestation (ASD). In recent trials testing soil solarization for snapdragon production, clover control was higher with solarization than with the 67:33 formulation of methyl bromide chloropicrin at 224 kg/ha lb/A under metalized film, and was equivalent to methyl iodide and other methyl bromide treatments. Solarization treatments were also equivalent to the fumigants for control of other weed species. ASD combines heating through soil solarization with brief periods of soil saturation. Anaerobicity is measured using oxidation-reduction potential probes and a period of approximately seven days of anaerobic conditions have been reported necessary for control of soilborne diseases in parts of the US, the Netherlands, and Japan. Treatments in Florida included the addition of composted broiler litter to improve moisture retention, and molasses as a carbon source to stimulate microbial activity. In a raised bed application of ASD prior to planting of a bell pepper crop, control of nutsedge emerging though the plastic at mid-season was equivalent to methyl bromide. Although variable, weeds emerging through plant holes at mid-season were reduced in all treatments receiving four acre inches of water at the onset of the trial when compared to the untreated check. At pepper harvest there were few significant differences between ASD treatments and the untreated check with regard to nutsedge emerging through the plastic, but all treatments had fewer weeds emerging through the plant holes than the untreated check.