Lima Bean Fungicide Update

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

I was disappointed to learn that our 24c special local needs label for Phostrol fungicide for downy mildew has expired. This means that it is not registered for use on lima beans in Delaware. NuFarm Americas is pursuing labeling of Phostrol for legume vegetables, including limas, so by next season we may not need the 24c label to use this product. The active ingredients in Phostrol are mono- and di-potassium salts of phosphorous acid, this is one of several fungicides that we call phosphonate fungicides. These same ingredients are found in Prophyte and K-phite which have labels for use on beans for downy mildew. I have tested Phostrol and a product that was never marketed here called Fungi-phite — both are excellent for downy mildew control. I would feel very safe to say the other labeled products with these same active ingredients should perform as well. I have Prophyte in my trial this year so I will be able to say for sure, if the test is successful.

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