Recent weather favors disease in all vegetable crops

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

The last two weeks have been especially favorable for disease development across most vegetable crops. Although late blight on tomatoes has not yet been detected in the state, the recent weather has been especially conducive to this disease developing. Tomato growers should be using a broad-spectrum fungicide such as chlorothalonil and/or mancozeb for managing the commonly occurring problems including Alternaria early blight and Septoria. These preventive fungicides when used every seven days offer good protection against late blight. If late blight on tomatoes is found in the state, then growers can add late blight specific products into their general disease management program to make their fungicide program more robust. An earlier Vegetable CAT article detailed the results of our late blight fungicide trial that was conducted last year. Results of this trial along with pictures of late blight are also available on It is especially important to be aware of home gardeners who may have late blight develop on their tomatoes in their backyards but not recognize the symptoms immediately or have the means to limit the disease and the corresponding spore production.

Downy mildew on cucumbers and other vine vegetables is another disease that we are looking for in the state. The spore traps have been operating in several Michigan counties for weeks, but thus far the sporangial counts have been very low. With the humid and overcast weather that we’ve experienced recently, the sporangial counts could change. Each day, the sporangial counts are updated on the downy mildew website that can be accessed at At this site, there are separate articles on how the sporangial counts are determined and the symptoms of downy mildew. Accompanying this article are the fungicide recommendations that have been developed over the years to manage downy mildew on cucurbits.

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