Cucurbit downy mildew confirmed in Ohio
- Frank Becker, OSU Extension Wayne County
- July 17, 2024
- 771
Cucurbit downy mildew has been confirmed for the first time in Ohio, specifically in Medina and Wayne counties. The observation was made by area growers and the Wayne County IPM Program and was confirmed by the C. Wayne Ellett Plant and Pest Diagnostic Clinic at the OSU CFAES Wooster campus.
This is almost an entire month earlier than when it was first found in 2023. Western New York had several confirmed cases during the last week of June, and Southern Michigan has a confirmed observation that was reported the first week of July. The two farms outside of Homerville, where samples were taken from, ranged in severity and incidence, with one farm having a severe, mature infestation and the other in the very early stages of disease development and progression. The farm in Wayne County had a moderate infection level.
Growers who have cucumbers and cantaloupe in their fields should take quick action to protect their crop. Cucurbit downy mildew is best managed with preventive applications before infection takes place. Once visual symptoms appear, control becomes increasingly difficult, and yield reductions may occur. In conditions are favorable for disease development and without effective, timely management, cucurbit downy mildew can cause rapid decline of the plant, severe defoliation and ultimately plant death in just a matter of days. Disease development is favored by rainy, humid conditions — relative humidity greater than 85% — and cooler temperatures of 60-70 F.
According to research trials completed in Ohio, Michigan, and other states and provinces around the Great Lakes region, the best fungicide options are as follows: Orondis Opti (FRAC 49+M05), Ranman (FRAC 21), Omega (FRAC 29), Previcur Flex (FRAC 28) and Elumin (FRAC 22). These should be tank mixed with chlorothalanil (Bravo, Equus, et cetera) or mancozeb (Dithane, Manzate, et cetera). Orondis Opti is a premix already containing chlorothalanil, but at a reduced rate. Fungicides have restrictions on how much product can be applied and how often, so follow the label. The label is the law. The more effective fungicides should be rotated to avoid resistance development in the pathogen.
Growers in Ohio also should intensify scouting of cucumbers and melons. Look for yellow or tan angular lesions delimited by veins on the top surface of leaves and fuzzy gray/brown growth on the undersides of the lesions. With a good hand lens or a smartphone camera with high magnification, you may be able to see small dark brown/purple spots within the fuzzy growth. These are the spores of the downy mildew pathogen. You also can utilize the Cucurbit Downy Mildew IPM Pipeline website, where you can sign up for alerts notifying you of nearby confirmed cucurbit downy mildew observations.
If you suspect downy mildew in cucumber or melon, submit samples to the C. Wayne Ellett Plant and Pest Diagnostic Clinic for confirmation. Instructions for sample submission are on their website. Call or email Dr. Francesca Rotondo at 330-263-3721 or rotondo.11@osu.edu with any questions. You also can work with your county extension educator to get samples submitted to the lab.
A major thank you to Dr. Rotondo and her staff in the Plant and Pest Diagnostic Clinic for their critically important work. Also, thanks to financial support from the Ohio Produce Growers and Marketers Association’s Ohio Vegetable and Small Fruit Research and Development Program. There is no fee for this service for Ohio vegetable growers.
Frank Becker is the agriculture and natural resources extension educator with Ohio State University Extension Wayne County and a certified crop adviser and may be reached at 330-264-8722 or becker.587@osu.edu.