Use of Precipitation Duration Data from Weather Radar in Leaf Wetness Estimates for Plant Disease Management

The duration of precipitation events is important knowledge for plant disease management since decisions on spray timing are often based on leaf wetness duration along with temperature during the wet period. Many of the physical models developed for estimating leaf wetness during rain events depend on the input of precipitation duration. The spatial diversity of precipitation events is critical information; however it is not typically captured through the use of rain gauges at weather stations. The data gathered from rain gauges is useful but site-specific, and thus not appropriate for use in a large farming community. To provide accurate guidance to a larger group of farmers regarding fungicide applications, the use of radar rainfall occurrence estimates may be a valuable alternative or may enhance sparse rain gauge networks. Because individual crop leaves generally retain less than 1mm of rain, it is important to focus on the duration of rainfall suggested by the radar data rather than the amount of rain.

Data for this project was obtained from the King City and Exeter Radar sites in southern Ontario for the 2001, 2002 and 2003 growing seasons. In this study, radar estimates of rain occurrence are compared to the detection of precipitation by tipping bucket rain gauges, at weather stations maintained by Environment Canada, the Grand River Conservation Authority and the Ontario Weather Network. The ability to determine precipitation duration from radar rainfall estimates will also to be tested at several sites in southern Ontario during the growing season of 2004 and some results from this summer will be included in the presentation. The weather radar estimates of precipitation will be evaluated against the accuracy required for operational use in plant disease management.