Development of Stem Rot (Caused by Sclerotium rolfsii ) in Peanut in Alabama

Abstract

Stem rot, or southern blight, caused by the fungus Sclerotium rolfsii, is an important disease of peanut in the southeastern U.S. Incidence and apparent onset of stem rot varies from year to year depending on planting date, weather conditions, and other factors. In order to more fully understand the effects of weather on stem rot, disease progress was evaluated through the 1995, 1996, and 1997 cropping seasons. Evidence of S. rolfsii was observed on peanut roots and crowns as early as 20 d after planting (DAP), which was 1 to several wk before stem rot lesions or plant wilt were observed. Disease measures tended to be lower in 1997 than in preceding years even though more rainfall and more consistent soil moisture were noted in 1997. Soil moisture was frequently in excess of field capacity from rainfall and may have contributed to suppressing stem rot development in 1997, perhaps by limiting oxygen availability. In 1995 and 1996, rainfall patterns were more normal and irrigation contributed to greater stem rot incidence. However, low moisture, specifically 7 d with < 1.8 cm rain, was associated with increases in numbers of dead plants, perhaps due to cumulative stress from disease and lack of moisture. Areas under disease progress curves for stem rot tended to be greater for early plantings compared to late plantings. However, by ca. 118 DAP, early plantings did not consistently have a greater incidence of dead plants, probably due to environmental conditions immediately preceding that date.