Cucumber beetles are common pests in our vegetable gardens. The most common species in California is the western spotted cucumber beetle, Diabrotica undecimpunctata. It is a greenish yellow insect with 12 black spots on its back.
Western spotted cucumber beetles are often confused with predaceous lady beetles. They can be distinguished by their antennae. Lady beetle antennae are short and stubby. Those of the cucumber beetle are long and threadlike.
A second species is the western striped cucumber beetle, Acalymma trivittata, which is yellowish orange with three black stripes.
Adult cucumber beetles attack the tender young growth of stems and leaves and the buds and petals on mature specimens. They may also eat ripening stone fruit. Larvae of the spotted cucumber beetle feed on the roots of corn, small grains, beans, sweet peas and several grasses. Striped cucumber larvae feed exclusively on the roots and leaves of cucumber, squash, pumpkins and melons.
Cucumber beetles also spread cucumber mosaic virus and bacterial wilt.
Beetles overwinter as adults in weedy areas, then move into planted fields as soon as seedlings emerge. They lay their yellow orange eggs at the base of plants or in soil cracks. Hatching larvae burrow into the ground seeking out roots. They feed for two to six weeks, pupate, and emerge as adult beetles that attack the above-ground portions of the plant. They can produce several generations each year.
Cucumber beetles are difficult to manage. The best strategy is placing protective cloth covers over emerging plants and removing them when plants are big enough to tolerate damage. Seedlings must be covered early before the insects are able to lay eggs under the cover.
In addition, natural predators, such as soldier beetles, tachinid flies, braconid wasps and certain nematodes, help control cucumber beetle populations.
For more information, visit www.ipm.ucannr.edu/PMG/GARDEN/VEGES/PESTS/cucumberbeet.html.
Linda Lewis Griffith is a UCCE Master Gardener.
Got a gardening question?
In San Luis Obispo call 781-5939, Arroyo Grande, 473-7190 and Templeton, 434-4105. Visit us at http://ucanr.org/sites/mgslo/ or email us at email@example.com. Follow us on Instagram at slo_mgs and like us on Facebook. Informative garden workshops are held the third Saturday of every month, 10 a.m. to noon at 2156 Sierra Way, San Luis Obispo. Garden docents are available after the workshop until 1 p.m. To request a tour of the garden, call 781-5939.
Don’t miss our Fall Plant Sale
Our 10th annual Tomato and Basil Tasting and Fall Plant Sale will be held Aug. 20.
Stop by between 10 a.m. and 2 p.m. to taste heirloom tomatoes, unique basil varieties, buy a few native or low water plants and visit our many educational booths. There are also workshops on gophers and ground squirrels, growing tomatoes and preserving tomatoes. Watch for next week’s article for more information. See you there!