Field Persistence and Efficacy of Five Bacterial Preparations for Control of Peanut Leaf Spot. G. R. Knudsen, Research Associate, Southern Region, ARS, USDA, Oxford, NC 27565, and Research Associate, North Carolina State University, Raleigh 27695-7616. H. W. Spurr, Jr., Research Plant Pathologist, Southern Region, ARS, USDA, Oxford Tobacco Research Laboratory, and Professor of Plant Pathology, North Carolina State University. Plant Dis. 71:442-445. Accepted for publication 20 November 1986. 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, 1987. DOI: 10.1094/PD-71-0442.

Five lyophilized bacterial preparations were evaluated in field trials for persistence and efficacy against Cercospora leaf spot of peanut (causal agent Cercospora arachidicola). Bacteria were applied as aqueous suspensions of wettable powders or as dusts, at biweekly intervals, to peanut cultivar Florigiant foliage at three locations in North Carolina and Virginia. Leaflets were sampled periodically to determine survival of applied bacteria and disease progression. Numbers of each bacterial strain recovered declined from about 10³–10⁴ cfu/leaflet (3 ? 10³–3 ? 10⁴ cfu/g fresh weight) to 10–10³ cfu/leaflet (30–3 ? 10³ cfu/g) over most 2-wk intervals. Background populations in untreated plots averaged about 10⁴ cfu/leaflet (3 ? 10⁴ cfu/g) and mostly consisted of gram-negative rod-shaped bacteria. Survival of gram-positive spore-forming bacteria (Bacillus spp.) formulated as wettable powder was less variable than survival of gram-negative, non-spore-forming Pseudomonas cepacia formulated as wettable powder or dust, and mean log populations were higher for Bacillus spp. However, P. cepacia controlled disease more effectively. End-of-season disease severity and area under the disease progress curve were significantly lower with several bacterial formulations than in control plots, but bacteria were less effective than the chemical fungicide chlorothalonil.