PHOTO: © Mary Howell Williams
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Spotted cucumber beetle Diabrotica undecimpunctata howardi
IDENTIFICATION — Adult beetles are 1/4 to 1/3-in. long and yellow to green with 11 black spots on their backs. The wormlike larvae are yellowish and start out about 1/8 in. long.
DAMAGE — Spotted cucumber beetle will attack most any type of flower, but also eats beans, tomatoes, cucumbers, melons and other edibles. Adults chew irregular holes in flowers, leaves and fruit from July to fall. The larvae (known as Southern corn rootworm) feed on corn roots in May, June and July, often transmitting bacterial wilt disease.
CONTROL — Beneficial nematodes can help. Buy them at local garden centers or mail-order sources, such as Gardens Alive. Mix the powder with water and water them into the soil late in the day in midsummer to control the larvae. For beetles, grow plants to attract natural predators (purple coneflower, hydrangea or Shasta daisy to attract soldier beetles, or angelica, thyme or yarrow to attract parasitic wasps). As a last resort, mix up and spray tops and undersides of leaves with horticultural oil or insecticidal soap (on overcast or cloudy days) as soon as you notice damage.
