Late in the day on July 31, cucurbit downy mildew was found on cucumber (Figure 1) in south-central Kentucky. Microscopy was used to confirm presence of the pathogen, by identifying its dark sporulation on the leaf surface (Figure 2) and oval, dark gray sporangia with rigidly branched sporangiophores and slightly curled sterigmata removed from the underside of the leaf.
With continued spread in Tennessee, it is likely that more cucurbits in Kentucky also have downy mildew. Crops in counties closer to the TN border are more likely to be affected. However, all growers should scout their cucurbits for this windborne disease, and growers of high-value crops (especially pumpkin, specialty gourds, and greenhouse cucumber) should consider making a downy mildew-specific fungicide
Very good options against downy mildew are the Orondis products or Ranman. Good options include Elumin, Previcur Flex, Tanos, Gavel, and Zampro. If a selected fungicide does not already contain a protectant like mancozeb or chlorothalonil, a tank mix is recommended. For lower-value cucurbits or those approaching the end of their season, a protectant application is still recommended with a product like mancozeb, chlorothalonil, or copper. See the University of Kentucky commercial vegetable guide (ID-36) for more information about cucurbit downy mildew fungicides.
As cucurbit crops approach the conclusion of their seasons, growers should remain active in terminating cucurbit crops to protect neighboring cucurbits from downy mildew. Abandoned cucurbits can be sources of downy mildew for other vining vegetables within several hundred miles of the affected farm. Since the downy mildew pathogen requires a living host, an herbicide application is a fast way to terminate a cucurbit crop the producer would otherwise abandon at this point in the season. Other ways to terminate the crops quickly include physical removal with burial or burning.
If a grower suspects downy mildew in their cucurbit crop, they should contact their local county agent immediately to submit a sample to a Plant Disease Diagnostic Lab. Rapid confirmation of downy mildew in cucurbit crops is critical, not only to maximizing yield, but also protecting neighbors' crops.
For more information contact the Pulaski County Extension Service at 606-679-6361. Learn about timely events or things to do in your home gardens by becoming a fan of Pulaski County Horticulture on Facebook, or following @hortagentbeth on Twitter, kyplants on Instagram, and Pulaski County Horticulture YouTube channel.
The Pulaski County Extension office is open to the public by appointment only through the month of August. Extension employees are still on the job and can be reached via office phone. Read the entire directive on the Pulaski County Cooperative Extension website at pulaski.ca.uky.edu.
A new load of pine straw is available now! Courtesy of the Lake Cumberland Master Gardeners. Pine straw is available to purchase on Tuesdays from 9am to 3pm at the Pulaski County Extension office.
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