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Disease Control and Pest Management

Ethanol Treatment—A Valuable Technique for Foliar Biocontrol Studies of Plant Disease. Harvey W. Spurr, Jr., Research plant pathologist, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Oxford Tobacco Research Laboratory, Oxford, NC 27565, and professor of plant pathology, North Carolina State University, Raleigh, 27650; Phytopathology 69:773-776. Accepted for publication 9 February 1979. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Association of Cereal Chemists, Inc., 1979. DOI: 10.1094/Phyto-69-773.

Ethanol treatment of tobacco leaf surfaces increased infection and reduced variation in disease indexes from inoculations with Alternaria alternata conidia. The ethanol treatment decreased the normal (resident) bacterial and fungal leaf microflora of greenhouse-grown tobacco leaf tissue 91 and 100%, respectively, without changing relative response of cultivars differing in susceptibility. Protective biocontrol of tobacco Alternaria leafspot resulting from applications of nonpathogenic A. alternata conidia was effective on both ethanol-treated and untreated leaf tissue. This indicated that nonpathogenic conidia can control leafspot without interacting with other leaf surface microorganisms but does not mean that leaf surface interactions between the protective fungus and other microorganisms do not occur and thereby alter control efficacy. A computer analysis showed a positive linear regression for probit disease index vs. log₁₀ inoculum dosage for all treatments. Comparisons of values calculated with the regressions indicated the ethanol and biocontrol treatments had separate but additive effects and may have altered disease indexes via the same mechanism. Ethanol treatment of leaf tissue should be valuable for studies of phyllosphere infection and interactions of microorganisms and for development of biocontrols.