OCCURRENCE OF POD ROT PATHOGENS IN PEANUTS GROWN IN NORTH-CAROLINA

Pod rot diseases historically caused significant losses in peanut prod uction in North Caroline. Advances in the understanding of pod rot dis eases and changes in cultural practices minimized losses in the years since 1979. By the early 1990s, however, some peanut growers began to observe pod rot that apparently was not associated with infection by c ommon soilborne pathogens. Incidence of pod rot also was high in resea rch plots used to study conservation tillage methods. Selected farms w ere surveyed in the fall of 1994, 1995, and 1996 to identify the fungi associated with pod rot symptoms in North Carolina. Over the three ye ars of the study, more than 6,000 symptomatic pods from 125 peanut fie lds were assayed for Rhizoctonia spp., Pythium spp., Cylindrocladium p arasiticum, Sclerotium rolfsii, and Sclerotinia minor. All five pathog ens were isolated during the field survey, with Pythium spp. and Rhizo ctonia spp. isolated most frequently. Rhizoctonia spp. were the domina nt pathogen in the majority of fields in 1994, whereas Pythium spp. pr edominated in 1995 and 1996. Combinations of pathogens were identified from 12 to 15% of pods; Rhizoctonia spp. + Pythium spp. and Pythium s pp. + C. parasiticum were the most frequent combinations. The mean est imated incidence of pod rot was 6.6% in 1995 and 5.9% in 1996. The eff ects of cover crops and tillage on pod rot incidence were studied in m icroplots in 1995 and 1996. In 1995, winter cover crops (wheat, oat, r ye, and fallow soil) did not affect pod rot incidence, but incidence w as greater in no-till treatments compared to plots with conventional t illage. Pod rot incidence did not differ among infestation treatments and no interactions among pathogen, cover crop, or tillage treatments were significant. In contrast, significant (P = 0.04) interactions amo ng winter cover crops and tillage occurred in 1996. Tillage did not af fect pod rot incidence following wheat or oats, but incidence followin g rye was much greater in no-till than in tilled plots.