Guess the Pest! Week #13 Answer: Ozone Damage

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations to Keith McGowan for correctly identifying the damage in the photo as ozone damage and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #13 Answer: Ozone Damage

Photo and article by Nancy Gregory

Ozone damage on vegetables is observed during hot and humid weather in our region. The most susceptible crops include potato, watermelon, cantaloupe, pumpkin, squash, snap bean, and lima beans. Symptoms occur on the top, younger leaves, and show up as dark spots on potato. On cucurbits, ozone damage shows up as yellowing with spots having a white crusty center. Watermelon is the most susceptible in this group. On beans, spots are small and bleached looking, and leaves may have a bronzed appearance on the top surface. Affected leaves may yellow and drop. Ozone is easily misdiagnosed and hard to accurately confirm, since an episode of air pollution cannot be chemically tested for. Inversion layers in hot humid weather result in trapped air at the field level that has a high level of air pollutants. Air remains at field level until winds pick up and disperse it, and four or five hours at levels of 80 ppb can result in damage. Some cultivars have some tolerance, and keeping plant stress low can help to avoid damage.

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