Biofumigation as an IPM Strategy

Biofumigation as an IPM Strategy

Summary

Managed decomposition of crop residue, biofumigation, is a biointensive strategy that has the potential to reduce the use of toxic biocides used to kill soilborne pathogens. Our study system is the early dying disease of potato (PED) caused by the fungus Verticillium dahliae and the root lesion nematode Pratylenchus spp. Potato early dying is a serious and chronic problem everywhere potatoes are grown and is currently managed using soil fumigation.

In 2008 we conducted an experiment evaluating forage pearl millet as a cover crop for suppression of root lesion nematodes and Verticillium. In earlier studies combining green manures with solarization, forage pearl millet was the only crop that performed comparably with and without tarping. Due to the engineering constraints of solarization, we decided to pursue forage pearl millet as a stand-alone biofumigation technology. The mechanism of pathogen suppression for this crop is unknown because, unlike Brassica spp., there are no chemicals released during decomposition with known toxicity to soilborne pathogens. Our study showed incorporating green manures of forage pearl millet and sorghum-sudangrass and weed controls was preferable to leaving the crop standing during the winter for suppression of PED pathogens. The suppressive nature of forage pearl millet residues for root lesion nematodes was verified in a laboratory experiment. In the spring of 2008, we assayed soils from an on-farm study initiated with growers in 2007. There was no statistically significant difference between commercial biofumigant Brassica mixtures and forage pearl millet for decreasing population densities of PED pathogens, but in 57% of the sites nematode densities were decreased in the millet plots as compared to only 25% in the Brassica plots. Population densities of root lesion nematodes remained high regardless of treatment, with an average across all sites of 166 nematodes per 100 cc soil. Disease pressure due to Vertcillium dahliae at the sites was below threshold in October 2007 prior to biofumigation and remained low the following spring. Cover crops and biofumigation were discussed with growers participating in the Healthy Grown program in two meetings and plots were viewed during two field days. These topics were also included in a conference call, a bioIPM meeting, and USDA tour of Healthy Grown farms. Over 100 growers participated in a presentation about PED and fumigation alternatives using an audience response system at the Wisconsin annual potato meeting. An invited research presentation was made at the Fifth International Congress of Nematology in Brisbane, Australia.

Objectives/Performance Targets

Build a knowledge base among growers and agribusiness representatives about ecosystem services available in the soil and the organisms involved.

Increase the expertise of farmers about cover crop management and the practice of biofumigation.

Increase awareness of farmers, crop consultants, county agents and industry representatives of the value of biofumigation relative to soil fumigation with synthetic chemicals.

Accomplishments/Milestones

Conducted an experiment in replicated plots at the Hancock Research Station evaluating forage pearl millet for biofumigation efficacy as compared to a weedy fallow and sorghum-sudangrass. The following comparisons were made for a cover crop planted in late June and incorporated in August: green manure vs. mulch, entire biomass incorporated vs residue remaining after harvesting shoots, and forage pearl millet vs controls (weeds, sorghum-sudangrass).

Conducted an experiment in the laboratory to study the impact of volatiles from decomposing forage pearl millet residues in soil on root lesion nematodes and Verticillium.

Conducted assays in the spring of 2008 to determine the efficacy of biofumigation in the fall of 2007 using commercial Brassica biofumigant mixtures, forage pearl millet, and other cover crops.

Interacted with growers participating in the Healthy Grown program in two meetings, a field day that included a tour of the millet research plots, a conference call, and a tour of farms for the USDA.

Discussed biofumigation with Protected Harvest, the national non-profit organization that independently certifies farmers’ use of stringent environmental growing standards in a meeting in Lodi, CA.

Presented information to Wisconsin potato farmers in both small (bioIPM meeting with 20 attendees) and large (Wisconsin’s annual potato meeting with more than 200 attendees) venues.

Presented information to Wisconsin potato farmers in the millet research plots during a potato field day at the UW Hancock Research Station.

Impacts and Contributions/Outcomes

Increased awareness of forage pearl millet, a new cover crop for Wisconsin potato growers during presentations and field days. We discussed the problems using Brassica spp. as biofumigants for managing root lesion nematodes. The timing of incorporation is so sensitive for Brassica spp. due to their excellent host status for root lesion nematodes, that we are no longer recommending these crops for biofumigation.

Our research with forage pearl millet cover crops has been very promising and we expect adoption to increase over time, but 2008 was a difficult year to shift growers’ behaviors. The Healthy Grown program struggled in 2008. The program has been successful at moving the product into the marketplace, but has not been able to command even a modest premium over the conventional product. New environmental standards for the management of natural areas surrounding Healthy Grown fields were added to the label, so growers have seen an increase in their costs (seed of native plants, managed burns, etc.) with no change in profit. In light of these constraints, the organization that provides oversight for the standards and certification postponed fumigation reduction goals until the Healthy Grown product is economically viable. The growers remain committed to the goal of reducing fumigation and remain receptive to information about biologically based alternatives but currently lack the financial incentives to do so.

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