Effect of Irrigation on Expression of Stem Rot of Peanut and Comparison of Aboveground and Belowground Disease Ratings. R. F. Davis, Assistant Professor, Department of Plant Pathology - CES, University of Georgia, Athens 30602-4356. F. D. Smith, Rohm & Haas Co., 727 Norristown Rd., Bldg. 4A, P.O. Box 904, Spring House, PA 19477-0904; T. B. Brenneman, Associate Professor, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, P.O. Box 748, Tifton 31793; and H. McLean, Sandoz Crop Protection, Cordele, GA 31015. Plant Dis. 80:1155-1159. Accepted for publication 1 July 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1155.

Field tests were conducted in 1993 and 1994 at a site with replicated irrigated and nonirrigated sections to evaluate the effect of irrigation on stem rot disease severity and on yield loss models, and to assess the relationship between aboveground and belowground disease ratings. The relationship between the number of cyproconazole applications and stem rot severity and peanut yield also were examined. Rainfall amounts were higher in 1994 than in 1993. Area under the disease progress curve (AUDPC) was calculated from weekly measurements of aboveground stem rot lesions. AUDPC, belowground disease ratings, and peanut yield were increased by irrigation in 1993 but not in 1994. Belowground disease ratings reflected AUDPC in irrigated and nonirrigated plots in 1993 and 1994, but the slopes of regression lines were greater in nonirrigated plots. Also, for any given AUDPC, the belowground rating was higher in the nonirrigated plots than in the irrigated plots. Increasing the number of cyproconazole applications decreased AUDPC and belowground disease ratings and increased yield. The results of this study indicate that the interrelationships of AUDPC, belowground stem rot ratings, and yield are strongly influenced by irrigation, but these effects do not carry over to subsequent crops. Either AUDPC or belowground stem rot ratings may be used in yield loss models, except in nonirrigated fields in dry years when belowground ratings must be used.

Keyword(s): Arachis hypogaea, Sclerotium rolfsii, white mold