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Ecology and Epidemiology

Epidemiology and Chemical Control of Phomopsis Canker of Highbush Blueberry. P. E. Parker, Graduate Research Assistant, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824; D. C. Ramsdell, Associate Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824. Phytopathology 67:1481-1484. Accepted for publication 20 May 1977. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1481.

Rain-dispersed Phomopsis vaccinii conidia from highbush blueberry (Vaccinium corymbosum L.) stem cankers were caught by the use of a funnel and jug spore trap. The major period of spore dispersal occurred during rains from bloom through petal fall in late May and June, and generally to a lesser extent, during rains in June and August. Populations subsequently declined and no conidia were detected in traps after September. Conidia were trapped from localized leaf lesions for only a short time during late August. Non-wounded bushes were not infected either with conidial or mycelial inoculum. Mechanically-wounded bushes were consistently infected after inoculations with mycelium throughout the growing season (April through October). Bushes experimentally damaged by freezing were infected by inoculation with conidia. Healthy nonwounded plants were not infected as a result of 1-mo exposures to natural field inoculum. In several cases, crowns of heavily diseased bushes were infected beneath the soil surface as evidenced by isolation of P. vaccinii onto potato dextrose-streptomycin agar. Difolatan and Benlate spray applications made during the growing season resulted in canker reductions of 36% to 58% (P = 0.10).