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Vegetables: Watch for the spotted and the striped cucumber beetle on cucurbit plants. Both beetles are yellowish-green and small — about one-quarter inch long. As you might guess, the striped beetle has stripes and the spotted one has spots. The striped species causes the most damage in Wisconsin. The beetles can both can transmit bacterial wilt, a lethal disease of cucurbits when they feed on melons and cucumbers. They also attack squash and pumpkins but don’t transmit the disease to these crops.

Infected plants first show wilting symptoms in individual leaves, followed by wilting and death of the entire plant. This should not be confused with wilting due to heat that happens on hot afternoons. If plants remain wilted in mornings and evenings, that is more likely to be bacterial wilt (or possibly infestation by squash vine borers). To be certain, cut through a wilted stem and hold the cut ends together for 10 seconds. Slowly pull the ends apart and look for whitish gooey material that forms a string and stretches between the two stem pieces. This material is a combination of plant sap and the bacterial wilt bacterium. For more information on cucumber beetles and their control, visit https://pddc.wisc.edu/ and enter “cucumber beetles” in the search box.

Basil downy mildew has recently been reported in southern Wisconsin for the first time in 2019. Basil downy mildew (BDM) can rapidly destroy entire basil crops. It is caused by the

fungus-like pathogen Peronospora belbahrii and can be transmitted on seed, infected plant parts, and on the wind. It thrives under moderate temperatures and high humidity, with symptoms progressing from the lower leaves upward. BDM can infect both ornamental and basil varieties grown as herbs.

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Characteristic symptoms include yellowing and downward curling of foliage and grayish-purple, fuzzy sporulation on leaf undersides. Infected plants should be removed and destroyed.

Only certain fungicides can protect plants from this disease and treatments must begin before symptoms develop. Harvesting early may be the best option for avoiding losses.

Rutgers University has developed some resistant basil varieties, Rutgers Devotion DMR and Rutgers Obsession DMR that you may want to grow in the future.

Lisa Johnson, Dane County UW-Extension horticulture educator

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