Survey of cereal diseases and petts in the Netherlands. 5. Occurrence of Septoria spp. in winter wheat

Data of the annual surveys of circa 100 commerical winter wheat fields were compiled to describe epidemics ofSeptoria spp. in the Netherlands during 1974–1986. In May, during the first node stage,S. tritici was dominant whileS. nodorum was virtually absent. In July, during ripening,S. tritici on average dominated overS. nodorum, though in the most continental districts of the countryS. nodorum predominated.In May between 1974 and 1984, on average 56% of the fields showed leaf infections bySeptoria spp., while in July between 1975 and 1986, on average 83% of the fields showed leaf infections. Prevalence ofSeptoria spp. has increased during the surveys. Annual intensity ofSeptoria spp. in winter wheat crops was positively correlated with precipitation and negatively with average monthly sunshine duration during the harvest-month August of the previous growing season. The correlation with sunshine during August could indicate that ascospores play a major role in subsequent epidemics; but whether it is a causal relation remains to be answered.Present address: Center for Agrobiological Research (CABO-DLO), PO Box 14, 6700 AA Wageningen, the Netherlands