Identification of weather conditions associated with the occurrence, severity and incidence of black seed disease of strawberry caused by Mycosphaerella fragariae.

Black seed disease (BSD) of strawberry is a sporadic disease caused by Mycosphaerella fragariae. Because little is known about potential crop losses or the weather conditions conducive to disease development, fungicides are generally not applied or are applied based on a pre-set schedule. Data collected from 2000 to 2011 representing 50 farm-years (total of 186 strawberry fields) were used to determine potential crop losses and to study the influence of weather on disease occurrence and development. First, logistic regression was used to model the relationship between occurrence of BSD and weather variables. Second, linear and non-linear regressions were used to model the number of black seeds per berry (severity) and the percentage of diseased berries (incidence). Of the 186 fields monitored, 78 showed black seed symptoms, and the number of black seeds per berry ranged from 1 to 10, whereas the percentage of diseased berries ranged from 3% to 32%. The most influential weather variable was total rainfall ...