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Epidemiology and Chemical Control of Godronia (Fusicoccum) 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 67:1475-1480. Accepted for publication 9 May 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1475.

A Burkard volumetric spore trap in continuous operation for two seasons in a highbush blueberry field heavily infected by Godronia cassandrae captured only negligible numbers of airborne conidia and ascospores of the pathogen. Rain-dispersed conidia were trapped by means of funnels attached beneath cankers and attached via tubing to jugs for collection. Conidia were most abundant from May through mid-June (blossom bud swell to petal fall). The number of conidia trapped ranged up to 1.21 × 105 conidia/ml of trapped rain water. Conidia were fewer in number from June through September and October (late leaf fall) than during April and May. The frequency of natural field infection was greatest from late April through June. Potted bushes inoculated with conidia also had the highest numbers of infections resulting from the April to June inoculation dates. Wounding was not required for infection since nonwounded inoculated plants consistently were infected during the growing season. Bushes exposed to ascospore inocula failed to become infected. In vitro germination of conidia was favored by temperatures of 22 and 30 C. Mycelial growth and infection of blueberry bushes was favored by temperatures of 10 C to 22 C. In fungicide field plot evaluations, captafol (Difolatan®) significantly reduced the numbers of cankers at one location by 82 to 95% [LSD (P = 0.01) = 0.12] and at another location by 52 to 65% [LSD (P = 0.01) = 0.21].

Additional keywords: Vaccinium corymbosum, fungicides.