ABSTRACT
A cooperative survey between member participants of an International Organisation for Biological Control (IOBC) Working Group was carried out in 1981–83. Data on the development of Septoria spp. in winter wheat crops across Western Europe were gathered and related to crop and weather factors. Hypotheses have been constructed concerning the ways in which S. tritici and S. nodorum cause attacks which could be distinguished as explosive or gradual. An epidemiological framework is described for S. tritici, based on these hypotheses and on the results of supporting experiments; a forecasting system is being developed and tested from this framework. In order to indicate the need to apply fungicide sprays, the system relies on monitoring (i) inoculum levels in crops before stem extension, and (ii) the degree by which rain splashes upwards during the period from stem extension to anthesis. Good disease control, with substantial increases in yield, was obtained from sprays guided by the scheme at Long Ashton in 1986, a year in which there was severe disease. However, a cool, wet spring triggered the system frequently and prevented its value for saving sprays from being tested. Development of the forecast system is continuing and, although results so far are very encouraging, its implementation will ultimately rely on advance knowledge of which Septoria sp. will predominate in a given year and locality.
