Development of a Weather-Based Advisory Program for Scheduling Fungicide Applications for Control of White Rust of Spinach

Development and validation of a weather-based warning system to advise fungicide applications to control dollar spot on turfgrass

Dollar spot is one of the most common diseases of golf course turfgrass and numerous fungicide applications are often required to provide adequate control. Weather-based disease warning systems have been developed to more accurately time fungicide applications; however, they tend to be ineffective and are not currently in widespread use. The primary objective of this research was to develop a new weather-based disease warning system to more accurately advise fungicide applications to control dollar spot activity across a broad geographic and climactic range. The new dollar spot warning system was developed from data collected at field sites in Madison, WI and Stillwater, OK in 2008 and warning system validation sites were established in Madison, WI, Stillwater, OK, Knoxville, TN, State College, PA, Starkville, MS, and Storrs, CT between 2011 and 2016. A meta-analysis of all site-years was conducted and the most effective warning system for dollar spot development consisted of a five-day moving average of relative humidity and average daily temperature. Using this model the highest effective probability that provided dollar spot control similar to that of a calendar-based program across the numerous sites and years was 20%. Additional analysis found that the 20% spray threshold provided comparable control to the calendar-based program while reducing fungicide usage by up to 30%, though further refinement may be needed as practitioners implement this warning system in a range of environments not tested here. The weather-based dollar spot warning system presented here will likely become an important tool for implementing precision disease management strategies for future turfgrass managers, especially as financial and regulatory pressures increase the need to reduce pesticide usage on golf course turfgrass.

Comparing Disease Predictors and Fungicide Programs for Late Blight Management in Celery

Late blight, incited by the fungus Septoria apiicola, is the most important foliar disease of celery in Michigan and results in necrotic lesions on leaves and petioles that can reduce yield up to 80%. Most celery growers apply the fungicide chlorothalonil as frequently as every 7 days to protect the crop; however, some of these applications may not be needed when environmental conditions do not favor disease development. The purpose of this study was to evaluate disease predictors using a standard (chlorothalonil) and a reduced-risk (azoxystrobin alternated with chlorothalonil) fungicide program for managing late blight on 'Dutchess' celery in 2003 to 2005. Fungicides were initiated 1 week after transplanting and reapplied every 7 days or according to the Septoria, Cercospora, or TOM-CAST predictors. The TOM-CAST predictor was tested using 10, 15, and 20 disease severity values (DSV) as thresholds for fungicide application. In each year of this study, timing sprays according to the TOM-CAST 10-DSV predictor resulted in disease control comparable with the 7-day interval, but required up to five fewer sprays and reduced fungicide costs up to $215/ha. The Septoria, Cercospora, and TOM-CAST 15-DSV predictors often provided control similar to the 7-day interval, but these predictors were somewhat inconsistent compared with TOM-CAST 10-DSV. The TOM-CAST 20-DSV predictor required the fewest number of sprays but unacceptable levels of disease resulted. The standard and reduced-risk fungicide programs frequently provided similar control; however, azoxystrobin alternated with chlorothalonil was more effective than chlorothalonil alone when disease pressure was high.