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Prediction of Potato Leafroll Virus Disease in Maine from Thermal Unit Accumulation and an Estimate of Primary Inoculum. O. P. Smith, Graduate Assistant, Department of Entomology, University of Maine, Orono 04469. R. H. Storch, Professor, Department of Entomology; P. R. Hepler, Associate Professor, Department of Plant and Soil Sciences; and F. E. Manzer, Professor, Department of Botany and Plant Pathology, University of Maine, Orono 04469.. Plant Dis. 68:863-865. Accepted for publication 30 March 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-863.

Prediction of the incidence of potato leafroll (PLR) virus disease for three areas of potato production was based on PLR incidence obtained from Maine’s potato certification program and temperatures recorded by the National Oceanic and Atmospheric Administration. For 1954–1976, area and year differences in PLR incidence were associated with the linear combination of the transformed percentage of primary inoculum and thermal unit accumulation above 21 C from 1–10 August. These two variables accounted for 62 and 80% of the variation in PLR incidence for cultivars Russet Burbank and Katahdin, respectively. Accurate PLR incidence was predicted for 1977 and 1978 but not for 1979. Possible explanations for this discrepancy are the absence of an aphid variable in the equations and an inaccurate estimate of the amount of primary inoculum present.

Keyword(s): covariance analysis, multiple-regression analysis, PLRV.