VIEW ARTICLE

Ecology and Epidemiology

Quantitative Assay by Elutriation of Peanut Field Soil for Sclerotia of Sclerotinia minor. D. M. Porter, Supervisory plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Tidewater Research Center, Suffolk, VA 23437; J. L. Steele, research agricultural engineer, Agricultural Research Service, U.S. Department of Agriculture, Tidewater Research Center, Suffolk, VA 23437. Phytopathology 73:636-640. Accepted for publication 17 November 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-636.

Sclerotia of Sclerotinia minor, causal agent of Sclerotinia blight of peanuts, can be elutriated from soil with a semiautomatic elutriator. Sclerotia were collected on 425-μm-mesh sieves during elutriation. The recovery of sclerotia from artificially infested soil following 3.0, 4.5, 6.75, 10.0, and 15.0-min of elutriation (~64 ml of water per second and ~231 cm³ of air per second per unit) was 65, 83, 92, 94, and 97%, respectively. Sclerotia can be found throughout the plow zone (20 cm depth) in fields with histories of Sclerotinia blight. The number of sclerotia at harvest in the top 2.5 cm of soil ranged from 10 to 35 per 100 g of soil in areas with symptoms of Sclerotinia blight. Sclerotia in the top 2.5 cm of soil readily survived winter temperatures of Virginia. One sclerotium per 100 g of soil was sufficient to cause severe disease. Continuous planting of nonhost crops, such as corn, greatly reduced soil populations of sclerotia. However, viable sclerotia in sufficient numbers to cause Sclerotinia blight remained in field soils not planted to peanuts for up to 41 mo. Based on these observations, rotations of up to 4 yr would not provide effective control of Sclerotinia blight in peanuts.