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Title: OBSERVATIONS ON INTEGRATED SYSTEMS USING BIOCONTROL WITH FERTILIZATION OR FUMIGATION TO CONTROL SCLEROTIUM ROLFSII

Author
item HOYNES, CHRISTINE - 1275-07-00
item Lewis, Jack
item Lumsden, Robert
item BEAN, GEORGE - UNIV. MD, COLLEGE PARK

Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Integrated systems to control soilborne plant pathogenic fungi are investigated to reduce the use of chemical fungicides in order to improve the quality of the environment and crop commodities. Greenhouse studies were performed with integrated control approaches to reduce viability of pathogen propagules in soil. Application of any of various nitrogen fertilizers at a field rate or of a biomass preparation of the biocontrol fungus Gliocladium virens (Gl-3) did not reduce viability of sclerotia. Application of fertilizer in combination with Gl-3 biomass significantly reduced viability. Ammonium sulfate was the most effective fertilizer. The addition of fertilizers along with biomass generally resulted in bean seed germination higher than that achieved with each individual component and almost eliminated disease. In soil fumigation with metham sodium and various biocontrol isolates, sub-lethal rates of the fumigant and conidia of the biocontrol isolates, but not biomass, reduced germination of sclerotia more than that obtained with either component alone. The results demonstrate the feasibility of integrated control approaches to reduce diseases of economic importance. The data also suggest that chemical rates, less than those currently used, can effectively reduce disease and pathogen inoculum in integrated systems along with possible replacement of methyl bromide. The approaches can be readily implemented in farm operations.

Technical Abstract: Two integrated control systems to reduce the pathogen Sclerotium rolfsii were investigated. In the first system, a normal field rate of nitrogen fertilizers was added with two rates of Pyrax/biomass powder of isolate Gl-3 of Gliocladium virens to a natural soil infested with sclerotia of isolate Sr-1 of the pathogen. The fertilizers or a low rate (0.05 mg/g) of fG1-3 biomass each applied to soil alone did not reduce viability of sclerotia. In soil treated with any fertilizer (0.09 mg of N/g) together with the low rate of Gl-3 biomass, sclerotial viability was significantly reduced. The most effective treatment to reduce viability was ammonium sulfate and the low rate of Gl-3 biomass. The addition of fertilizers along with the low rate of biomass generally resulted in germination higher than that achieved with each individual component. Disease severity on beans in pathogen-infested soil treated with the fertilizer and the low rate of Gl-3 biomass, was almost eliminated. In fumigation studies with metham sodium, a dosage response against viability of Sr-3 sclerotia indicated that fumigant rates of <17.1 microgram were inhibitory to Gl-3 biomass but not to conidia. Consequently, conidia of Gl-3, of isolate Thm-4 of Trichoderma hamatum, and of isolate Tv-1 of T. viride were used together with metham sodium at a rate of 17.1 microgram/g of soil. Conidia applied to soil 2 days before this rate of metham sodium reduced viability of Sr-3 sclerotia more than each individual component.