Commercial vegetable production is an important component of the Wayne County agricultural economy. Therefore, it is important to keep up to date on the progression of major diseases affecting vegetable producers. Just last week, cucurbit downy mildew was confirmed just north of Wayne County line in Medina County. Downy mildew is a potentially devastating disease of cucurbit crops, but especially cucumbers and cantaloupe. Pumpkins, squash and watermelon are at less risk of severe damage from downy mildew.
According to Sally Miller, OSU Extension Vegetable Disease specialist, after downy mildew has been found in the area all growers should be on a fungicide management program. This is because downy mildew is considered a “community” disease. It is not going to stay isolated on one farm or field; it can move through the air and spread over a long distance. The recommendations shared by Sally Miller from Michigan State’s Dr. Mary Hausbeck are a rotation of the following fungicides tanked mixed with chlorothalanil or mancozeb: Ranman, Elumin, Zampro, Previcur Flex, or Orondis Opti (no need to tank mix Orondis Opti since it is a premix with chlorothalanil). Make sure to check the labels for use restrictions and preharvest intervals (PHIs). Note that the fungicides recommended above have different pre-harvest intervals. Keep this in mind when fungicides are applied after harvesting begins.
Additionally, in cucurbit crops, powdery mildew is starting to get a foothold in the area. Powdery mildew spots appear on the leaves of the plant and expand eventually resulting in leaf death. Sally Miller points out that powdery mildew can be especially frustrating to pumpkin growers as the disease can also attack the “handles” which results in weakened pumpkin handles. An important aspect of management of powdery mildew, and really for any pesticide use, is to practice rotation between modes of action to avoid build up of resistance. Rotating between products such as Aprovia Top, Bravo Weather Stik, Fontelis, Miravis Prime, Procure, Quintec and Rally give you a good range of FRAC (Fungicide Resistance Action Committee) groups that indicate different modes of action.
Two other diseases that both commercial and home tomato growers struggle with this time of year are septoria leaf spot and early blight. Both of these fungal diseases start at the bottom of the plant and work their way up the plant. Septoria leaf spot is characterized by small, roughly circular spots that have dark margins and a tan center. As the disease progresses spots enlarge and can cause premature leaf drop. Under warm, moist conditions, defoliation can be rapid. Early blight symptoms consist of small, irregular, dark brown to black, dead spots ranging in size from a pinpoint to 1/2 inch in diameter. As the spots enlarge, concentric rings may form giving a “bull’s eye” or “target spot” appearance. There can be a narrow, yellow halo around spots. As the disease progresses spots can grow together and cause leaf death. Unlike septoria leaf spot, early blight can also affect the tomato fruit.
Both diseases generally start by soil splashing onto the lower leaves during a rainfall event. Control strategies involve pruning off lower leaves and branches, mulching around plants to prevent soil splashing, removing, and destroying infected leaves, and use of a protectant fungicide such as Daconil (active ingredient chlorothalanil) on a weekly schedule when rains are frequent.
Frank Becker is an OSU Extension Agriculture and Natural Resources Program Assistant and IPM Program Coordinator. He may be reached at 330-264-8722.
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