FIELD SPREAD OF ANTHRACNOSE FRUIT ROT OF STRAWBERRY IN RELATION TO GROUND COVER AND AMBIENT WEATHER CONDITIONS

Strawberry plots of the everbearing cultivar Tristar were established in each of 2 yr in Ohio. Ground cover between and within rows consisted of plastic, straw, or bare soil. Fruit infected by Colletotrichum acutatum (cause of anthracnose fruit rot) were introduced immediately before a rain episode in all plots except controls (which had no soil cover). Seven days after the rain, fruit disease incidence in row segments within 61 cm of the inoculum source was 0.19, 0.07, 0, and 0 for plastic, soil, straw, and uninoculated control plots, respectively, in 1990; in 1991, incidence was 0.16, 0.07, 0, and 0 for plastic, soil, straw, and controls, respectively. In general, disease incidence declined with distance from the inoculum source, an indication that the introduced infected fruit were the source of spores for rain splash dispersal. Cumulative incidence of disease at the end of the season was consistent with results for 7 days after infestation. Disease incidence in the plastic and soil plots was related to weather variables using stepwise regression analysis. The best relationship was based on the product of four terms: rain amount (cm), days from introduction of inoculum minus 6, an index of infection (0-1) based on wetness duration starting with a rain episode and average temperature during the wetness period, and an ordered distance from the spore source (1-3; 1 for closest, 3 for greatest distance and separated by a row of plants). Results confirm previous controlled studies with a rain generator that surface topography or ground cover greatly affects dispersal of spores by rain splash and that the use of straw mulch reduces disease incidence.