Downy Mildew and Powdery Mildew

CucCAP Plant pathologists discussed cucurbit diseases reported by growers in Growing Produce Magazines’ 2023 State of the Vegetable Industry Survey.

Mary K. Hausbeck and Sheila D. Linderman of Michigan State University explain that Downy mildew is well-known for causing catastrophic losses in a brief period of time. It spreads to surrounding fields on air currents via tiny, microscopic spores that act as seeds of the pathogen. Cool (~ 60°F), wet, and cloudy conditions create an ideal environment for DM spores to survive outside the host.

disease symptoms on leafAnthony Keinath of Clemson University explains that Powdery mildew can reduce watermelon yields directly by causing the plants to produce fewer fruit, and indirectly by killing leaves that shade the fruit, leading to sunburn. The losses can be up to $1,500 per acre, or 75% of the value of the crop. Powdery mildew also can cause pumpkins to set fewer fruit, delay fruit ripening, and cause the handles to be soft, so they don’t hold up when the fruit are sold.

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