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 consiste d of plastic, straw, or bare soil. Fruit infected by Colletotrichum ac utatum (cause of anthracnose fruit rot) were introduced immediately be fore a rain episode in all plots except controls (which had no soil co ver). Seven days after the rain, fruit disease incidence in row segmen ts within 61 cm of the inoculum source was 0.19, 0.07, 0, and 0 for pl astic, soil, straw, and uninoculated control plots, respectively, in 1 990; in 1991, incidence was 0.16, 0.07, 0, and 0 for plastic, soil, st raw, and controls, respectively. In general, disease incidence decline d with distance from the inoculum source, an indication that the intro duced infected fruit were the source of spores for rain splash dispers al. Cumulative incidence of disease at the end of the season was consi stent with results for 7 days after infestation. Disease incidence in the plastic and soil plots was related to weather variables using step wise regression analysis. The best relationship was based on the produ ct of four terms: rain amount (cm), days from introduction of inoculum minus 6, an index of infection (0-1) based on wetness duration starti ng with a rain episode and average temperature during the wetness peri od, 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 co nfirm previous controlled studies with a rain generator that surface t opography or ground cover greatly affects dispersal of spores by rain splash and that the use of straw mulch reduces disease incidence.