Effect of the Herbicide Ethalfluralin on Net Blotch Disease of Peanut Pods. Y. Ben- Yephet, Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel. S. Mhameed, Z. R. Frank, and J. Katan. Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Bet Dagan 50250, Israel; and Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel. Plant Dis. 75:1123-1126. Accepted for publication 6 April 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/PD-75-1123.

Five field experiments and one container experiment were conducted during three successive years to evaluate the effect of ethalfluralin and vernolate on the incidence and severity of net blotch disease of peanut (Arachis hypogaea) pods in which unspecified actinomycetes seem to be involved. In all experiments, the incidence of diseased pods (range 38–86%) was significantly higher in the plots treated with a mixture of the two compounds than in the control plots without herbicides (range 25–48%). The range of disease severity ranked on a 0–10 rating scale was 0.44–2.13 and 0.25–0.83 in herbicide-treated and control plots, respectively. Disease incidence and severity on pods in soil treated with fenamiphos and metham-sodium, with and without herbicides, were similar to the levels observed in the control plots without herbicides. Application of methyl bromide, alone or with herbicides, reduced the disease considerably. Ethalfluralin alone increased disease incidence, and this increase was not affected by the addition of vernolate. Ethalfluralin was moderately toxic to bacteria but not to fungi or actinomycetes in growth media; vernolate was not toxic to any of the microorganisms. Infestation of soil with mixed cultures of actinomycetes isolated from diseased pods reproduced net blotch disease symptoms on the pods.