EFFECT OF IRRIGATION ON EXPRESSION OF STEM ROT OF PEANUT AND COMPARISON OF ABOVEGROUND AND BELOW-GROUND DISEASE RATINGS

Field tests were conducted in 1993 and 1994 at a site with replicated irrigated and nonirrigated sections to evaluate the effect of irrigati on on stem rot disease severity and on yield loss models, and to asses s the relationship between aboveground and belowground disease ratings . The relationship between the number of cyproconazole applications an d stem rot severity and peanut yield also were examined. Rainfall amou nts were higher in 1994 than in 1993. Area under the disease progress curve (AUDPC) was calculated from weekly measurements of aboveground s tem rot lesions. AUDPC, belowground disease ratings, and peanut yield were increased by irrigation in 1993 but not in 1994. Belowground dise ase ratings reflected AUDPC in irrigated and nonirrigated plots in 199 3 and 1994, but the slopes of regression lines were greater in nonirri gated plots. Also, for any given AUDPC, the belowground rating was hig her in the nonirrigated plots than in the irrigated plots. Increasing the number of cyproconazole applications decreased AUDPC and belowgrou nd disease ratings and increased yield. The results of this study indi cate that the interrelationships of AUDPC, belowground stem rot rating s, and yield are strongly influenced by irrigation, but these effects do not carry over to subsequent crops. Either AUDPC or belowground ste m rot ratings may be used in yield loss models, except in nonirrigated fields in dry years when belowground ratings must be used.