Environmental Factors Influencing Airborne Ergot Ascospore Concentrations in Kentucky Bluegrass Grown for Seed in Central Oregon

Series/Report Number: COARC2014

Abstract: Ergot, caused by the fungus Claviceps purpurea, is an important disease affecting Kentucky bluegrass seed production in central Oregon. Multiple fungicide applications are routinely applied before and during flowering, but fungicide applications during anthesis provide only partial control of ergot. Since the ergot fungus requires unfertilized ovaries for infection, ascospores must be present during anthesis in order for successful infection to occur. In some years, ascospore production does not always coincide with anthesis or they are not present and in these years fungicide applications would not be necessary to control the disease. However, in other years extremely high numbers of ascospores can be present and cause severe epidemics. The objective of this research was to identify environmental factors that contribute to ascospore production and develop a model for the prediction of ascospore production events in Kentucky bluegrass fields of central Oregon. Only 55 spores were captured during the 55 day period which limited the ability to develop a predictive model. However, several factors were identified that were significantly (P ≤ 0.0009) related to spore production including a minimum air temperature of 41° F, mean soil temperature of 61° F, minimum soil temperature of 53° F, maximum soil temperature of 70° F, and a volumetric water content between 25 and 30%. These results are consistent with previous studies in perennial ryegrass seed production systems. Additional data will be needed to develop a predictive model for ergot ascospore production that can be used as a tool by growers to make more informed fungicide application decisions.