The Effect of Primary Inoculum Level ofPyrenophora tritici-repentison Tan Spot Epidemic Development in Wheat

There were significant positive relationships between the area under the disease progress curves and the level of primary inoculum for both years, even though weather conditions were very different, 1987 being very wet and 1988 very dry. Statistical analysis indicated, however, that the quantitative effect of local primary inoculum on epidemic development differed between the two years; thus, the importance of local primary inoculum, relative to incoming secondary inoculum, is likely to depend on the particular conditions of the epidemic. The experiments indicated that pathogen control measures that reduce residue-borne primary inoculum can decrease epidemic development and crop damage, despite multiple infection cycles caused by wind-disseminated secondary inoculum