VIEW ARTICLE

Ecology and Epidemiology

Eutypa armeniacae in Michigan Vineyards: Ascospore Production and Survival, Host Infection, and Fungal Growth at Low Temperatures. A. T. Trese, Graduate research assistant, (Agricultural Research, Science and Education Administration, U.S. Department of Agriculture), Michigan State University, East Lansing 48824; C. L. Burton(2), and D. C. Ramsdell(3). (2)Research plant pathologist (Agricultural Research, Science and Education Administration, U.S. Department of Agriculture), Michigan State University, East Lansing 48824; (3)Professor of Plant Pathology, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824. Phytopathology 70:788-793. Accepted for publication 29 February 1980. 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, 1980. DOI: 10.1094/Phyto-70-788.

The seasonal abundance of airborne Eutypa armeniacae ascospores was sampled over a 2-yr period at two Vitis labrusca ‘Concord’ vineyards in southern Michigan. Burkard volumetric recording spore traps placed within vineyards were encircled with a 2-m-diameter circle of diseased vine trunks bearing mature perithecial stromata. Airborne ascospore octads were found only after stromata had been exposed to a minimum of ~2 mm of rainfall at temperatures > 0 C. Free water (vine trunk wetness) maintained by prolonged rain resulted in continued dispersal of ascospore octads. The highest octad concentrations were evident in spring (late February through April): this peak was followed by a decline in the summer (June through August) and a rise in numbers of octads dispersed in September, October, and November. No octads were trapped from mid-December through late February, because of subfreezing weather conditions during which no rain fell. Under laboratory conditions, ascospores maintained a high level of viability after subjection to long periods of freezing and to repeated cycles of freezing and thawing. Alternate wetting and drying had an adverse effect on spore germination. Such conditions are prevalent in the field during the periods of maximal inoculum dispersal, which coincide with the main part of seasonal vine pruning operations. Mycelium grown in vitro was capable of renewed growth after freezing. Controlled inoculations of 1- and 2-yr-old pruning cuts made on potted 4-yr-old vines held at –1 to 1 C resulted in a low level of infection during the winter months.