An Assessment of Environmental Conditions Preceding Outbreaks of Sclerotinia Blight of Peanut in Virginia1

Abstract

Abstract Records of outbreaks of Sclerotinia blight of peanut at the Tidewater Center in Suffolk were summarized over a 16-yr period (1978–93). Initial outbreaks of the disease were determined through intensive scouting of fields at weekly intervals. First occurrences of Sclerotinia blight occurred between 10 July and 7 Sept., or 62 to 120 d after planting (DAP). The mean and median dates of initial outbreaks were 28 July (79 DAP) and 25 July (76 DAP), respectively. The initial onset of disease always occurred after vines were within 15 cm of touching between rows or after vines had lapped between rows. Under these conditions, a canopy of dense foliage shaded the soil surface and infection sites inside rows from direct sunlight. Rainfall summaries showed the heaviest accumulations were from 6 to 15 d before disease outbreaks. Maximum and minimum air temperatures over the 15-d period prior to disease onset averaged ca. 32 C and 20 C, respectively. Maximum and minimum soil temperatures at the 10-cm depth averaged ca. 30 and 25 C, respectively, during this same period. The results of this study provide evidence that vine growth and rainfall are primary determinants in triggering the onset of Sclerotinia blight of peanut in southeastern Virginia.