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Factors influencing Erysiphe necator ascocarp overwintering and ascospore release of in the Willamette Valley of Oregon
L. THIESSEN (1), W. F. Mahaffee (2). (1) Oregon State Univ, Corvallis, OR, U.S.A.; (2) USDA ARS, Corvallis, OR, U.S.A.

Exotic plant hosts and pathogens often display asynchronous development outside their native range, which may influence disease forecasting and management. In the Willamette Valley of Oregon, the development and maturation of <i>E. necator</i> ascocarps occurs asynchronously to the host, as the discharge of ascospores often occurs prior to bud break or much later in the host development. Cleistothecia were collected from commercial vineyards in the Willamette Valley prior to precipitous weather (October 9, 2012 and October 24, 2013) and were embedded onto artificial-bark substrates or grape trunk pieces. Infested bark substrates were then suspended above impaction spore traps. In addition, spore traps were placed adjacent to grapevine trunks naturally infested with <i>E. necator</i> ascocarps. Traps were collected biweekly and were processed using quantitative polymerase chain reaction specific for <i>E. necator</i>. Airborne <i>E. necator</i> DNA was detected from November through late April during periods considered favorable for ascospore release (e.g. > 2.5mm precipitation and average temperature during wetness events > 7°C) until late April. These data indicate that <i>E. necator</i> ascocarp maturation needs to be further examined to better predict disease development in subsequent seasons.

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