6-22-2012

Disease Forecasting

Predicting disease outbreaks is similar to predicting the weather in that neither is very accurate. The best that one can do is to explain the environmental conditions under which they occur and hope you are correct. One of the keys for the development of foliar diseases like dollar spot, brown patch, Pythium blight and foliar anthracnose is high humidity. The temperature requirements vary for these diseases, but regardless of the temperature, they will not occur when the humidity is low. Crown rot anthracnose infection occurs following periods of constant rainfall. Take all patch and summer patch infections also take place during periods of heavy rains or constant rainfall. The disease symptoms for all 3 of these diseases are more severe when periods of excess rainfall are followed by high temperatures and drought stress, much like many parts of Michigan are experiencing.  

I know we would all like to be able to predict when these diseases are going to occur several days in advance based on weather forecasting, but as I like to say, weather forecasters are the only people I know who can be wrong over 50 % of the time and still keep their jobs! Because of the variations in temperatures that occur in Michigan, the best solution for these diseases is to be on a preventive fungicide program based on historical data and environmental conditions. Dollar spot may be a problem all season long but, historically, will be especially bad in August and September. Brown patch and Pythium blight will be most severe in July and early August, and crown rot anthracnose will be most severe during July and August. Some additional parameters for the development of these and other diseases, along with helpful diagnostic descriptions can be found on the MSU turf diseases website, www.msuturfdiseases.net.   

J. M. Vargas, Jr.

Professor

Michigan State University