By Clint Thompson
Powdery mildew disease is present on older squash in various vegetable fields across South Florida. According to the South Florida Vegetable Pest and Disease Hotline, respondents report that the disease has also started to show up on watermelon crops across the region as well.
It’s also reported that powdery mildew is showing up on squash and cantaloupe in the Manatee Ruskin area.
The disease thrives in high humidity, making the Southeast region a prime target for powdery mildew. Places in Georgia, Florida and Alabama are especially vulnerable the next two weeks. Temperatures in Tifton, Georgia are expected to go back up into the 80s this week and 90s next week. And there’s little to no chance of rainfall. It’s the same forecast for Mobile, Alabama, whose best chance of rain is a 40% chance on Monday, May 18 and Saturday, May 23. Temperatures in Tampa, Florida are going to be in the high 80s the next two weeks.
The disease can develop rapidly under these favorable conditions.
Symptoms on watermelon plants appear as yellow blotches on the oldest leaves first. If the disease is left untreated, the fungus spreads to the entire leaf. These blotches become bronzed and turn dark brown or purplish as the disease progresses during the season. Eventually the leaf dies and has a crisp texture.
Powdery mildew normally appears in the middle of the production season. Preventive treatments can help maximize the crop’s yield potential and prevent plant damage. Growers need to scout fields regularly to know if the disease is a factor in their fields.
There are some vegetables that can tolerate or are resistant to the disease. Most commercial cucumber varieties grown in Florida have acceptable levels of resistance.
Podosphaera xanthii and Erysiphe cichoracerarum, are the two pathogens that cause powdery mildew disease on cucurbits, particularly cucumbers, year-round. P. xanthii is an aggressive pathogen that attacks during warmer months. E. cichiracearum strikes during cool spring and early summer.