Alternatives to methyl bromide soil fumigation for vegetable and floriculture production
Location: Subtropical Plant Pathology Research
Title: Field evaluation of anaerobic soil disinfestation in a bell pepper-eggplant double crop
Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: October 11, 2009
Publication Date: October 15, 2009
Citation: Butler, D.M., Rosskopf, E.N., Burelle, N.K., Muramoto, J., Shennan, C. 2009. Field evaluation of anaerobic soil disinfestation in a bell pepper-eggplant double crop. Proceedings of International Research Conference on Methyl Bromide Alternatives. 43:1-4.
Interpretive Summary: There is considerable interest in the development of non-chemical alternatives to the fumigation of soil with methyl bromide. Anaerobic soil disinfestation (ASD) incorporates two well-studied and effective methods, biological soil disinfestation and soil reduction sterilization . Soil treatment by ASD utilizes principles behind solarization and flooding to create elevated soil temperatures and anaerobic soil conditions through saturation of the topsoil, tarping with an oxygen-impermeable plastic, and the addition of a labile carbon source to stimulate microbial activity. During the 2008-2009 vegetable season, the ASD approach was applied to the raised-bed, plastic mulch system commonly used in Florida production. The field trial consisted of multiple approaches to identify the optimal combination of composted broiler litter, molasses as a carbon source and water for the creation of a strong anaerobic condition. Broiler litter significantly increased water holding capacity. Treatments utilizing litter and high water content controlled several types of weeds, both in the plant hole and coming through the plastic during the principal bell pepper crop as well as in the double crop of eggplant.
As a response to the global phase-out of methyl bromide (MeBr) as well as the limitations of fumigant alternatives to MeBr, there is a need for non-chemical options for controlling weeds, soil-borne pathogens, and plant-pathogenic nematodes in vegetable production systems. Anaerobic soil disinfestation (ASD) incorporates two well-studied and effective methods, biological soil disinfestation and soil reduction sterilization . Soil treatment by ASD utilizes principles behind solarization and flooding to create elevated soil temperatures and anaerobic soil conditions through saturation of the topsoil, tarping with an oxygen-impermeable plastic, and the addition of a labile carbon source to stimulate microbial activity. The tarp is left in place for sufficient time to increase soil temperatures and allow soil microbial communities to create strongly anaerobic conditions. A complete factorial field experiment with three levels of initial irrigation (10, 5, 0 cm), two levels of poultry litter (amended, unamended), and two levels of molasses (amended, unamended), in combination with solarization was established in August 2008 and again in August 2009 to optimize ASD for Florida raised-bed vegetable production. Untreated (UTC) and MeBr controls were included in both years. Soil temperature, soil moisture, and soil anaerobicity were monitored continuously during the ASD treatment. Inoculum packets were introduced prior to ASD establishment to determine treatment impacts on survival of Phytophthora capsici. Soils were sampled before initialization of the experiment and periodically during the season to determine treatment impacts on soil pH, soil nutrients, soil physical properties, and nematodes. Following ASD treatment, bell peppers (Capsicum annuum) were planted in Sept. 2008 and eggplant (Solanum melongena) in Feb. 2009. Plots were regularly evaluated for treatment impacts on weed control, root galling caused by root-knot nematode, and crop growth and productivity. Based on data from the 2008-2009 field season, both molasses and broiler litter amendments were effective at increasing the strength of anaerobicity (as indicated by redox potential (Eh)) compared to the unamended treatments. Daily maximum soil temperatures in solarized treatments at 15-cm depth were near 45ºC, but less than 35 ºC in unsolarized treatments (MeBr and UTC). Control of yellow nutsedge (Cyperus esculentus) emerging from plant holes at the end of the double crop was equivalent to MeBr when plots were amended with either molasses or poultry litter and 10 cm of initial irrigation was applied. Control of yellow nutsedge emerging through plastic was inconsistent for each factorial treatment, although generally intermediate between MeBr and UTC. Control of P. capsici, introduced as buried inoculum, was equal to that of MeBr for all solarized treatments regardless of applied soil amendments or water. Control of plant-pathogenic nematodes in soil immediately following ASD treatment and prior to planting bell peppers was equivalent to MeBr for all treatments that included amendment with either molasses or broiler litter. However, in general, numbers of plant pathogenic nematodes present were low at that stage in the trial. Total yields of marketable fruit harvested from the bell pepper crop planted after ASD treatments were greater than the untreated control and equal to the harvest from the MeBr control for all but three treatments. Yields of eggplant exceeded the untreated control for all but four treatments, and in the case of treatments with applied litter or applied litter and molasses, exceeded yields observed from the MeBr control.