Look for brown to black lesions on the leaves that my disintegrate resulting in a tattered appearance to the leaves. There may also be elliptical lesions on the stems and leaf petioles. During wet weather, these lesions may be covered with a pink to buff-colored spor mass.
Crop rotation can help prevent the disease as can the use of clean seed. Crop rotations should be a minimum of 3 to 4 years long to prevent carryover of disease spored from crop debris. Periodic
fungicide applications may be necessary during wet weather in mid-summer. Apply chlorothalonil (Bonide Fungonil Concentrate, Daconil, Ortho Garden Disease Control, Fertilome Broad-Spectrum Landscape and Garden Fungicide, others) or mancozeb (Bonide Mancozeb Flowable). (Ward Upham)