Yellow rust does not like cold winters. But how to find out which temperature and time frames could be decisive in vivo?

Abstract

Yellow rust epidemics caused by Puccinia striiformis f. sp. tritici were monitored in winter wheat grown without fungicides at four locations over the years 2010–2016 in the Grand Duchy of Luxembourg (GDL) and were observed at increased frequency since 2014. A total of 29 field case studies were subdivided into epidemic and non-epidemic cases based on the control threshold of the disease defined in the framework of integrated pest management (IPM). Significant air temperature differences were found between the time courses of epidemic and non-epidemic cases during seven periods and seven individual days. The longest periods with significantly higher temperatures for epidemic cases were found between 21 and 28 days after sowing (DAS) and between 132 and 134 DAS, corresponding approximately to the time of winter wheat emergence, when the disease may infect the newly sown crop, and to the coldest period of the year, respectively. Average daily temperatures were 7.33 ± 0.32 °C and 10.79 ± 0.26 °C between 21 and 28 DAS for non-epidemic and epidemic cases, respectively. Between 132 and 134 DAS, average daily temperatures were − 1.62 ± 0.74 °C and 1.58 ± 0.43 °C for non-epidemic and epidemic cases, respectively. Based on the significant temperature differences detected, up to 86.7% of correct classifications were obtained by leave-one out cross-validation, suggesting that some of the temperature differences identified here have considerable prognostic value for forecasting if an economically relevant yellow rust epidemic must be expected or not.