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How does Botrytis cinerea infect red raspberry?
Olga Kozhar: Washington State University; Tobin Peever: Washington State University
<div><i>Botrytis cinerea</i>, causal agent of gray mold, is the most important pathogen of raspberry in the US Pacific Northwest and worldwide. Despite intensive fungicide application programs used to control the disease, fruit losses often exceed 25% due to incomplete disease control. Fungicides currently are applied on a calendar basis rather than based on inoculum pressure and infection risk because the disease cycle on red raspberry is poorly understood. The objectives of this study were to determine the dynamics of flower and fruit infection in association with environmental conditions. Recovery of <i>B. cinerea</i> from seven developmental stages of raspberry flowers and fruit in northwestern Washington was recorded in 2015-2016 in a field not sprayed with fungicides. Colonization of raspberry flowers by <i>B. cinerea</i> was limited (15%), increased as fruit developed, and peaked on mature fruit (67%). In early stages of flower development, the floral part with greatest <i>B. cinerea</i> recovery was the carpel (70%). As fruit matured, additional floral parts were colonized by <i>B. cinerea</i>, which could increase the risk of secondary infections of mature fruit. <i>B. cinerea</i> colonization of fruit was significantly associated with air temperature and rainfall. The results suggest that fungicide applications at flowering may be less effective than those at fruit development and maturation, and monitoring environmental conditions may help time fungicide applications effectively to control gray mold.</div>

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