The cucumber beetle, a pest that targets vine crops and cucurbits, is a ¼th to 1⁄5th of an inch menace to muskmelon and cucumber growers across the country. Ricardo Bessin of the University of Kentucky explains that there are two species of cucumber beetles. Both types, the striped and the spotted, reside in the Northeastern U.S. and can be recognized by their yellowish green color.
The aptly named striped cucumber beetle has three black stripes on its wings while the spotted cucumber beetle can be identified by its 12 black spots. The main difference between the two beetle types is that the spotted cucumber beetle is less discerning in its food of choice, attacking a large number of vegetables. It holds a secondary title of southern corn rootworm when found in field corn.
Life Cycle And Feeding
Bessin describes the beetle’s lifecycle saying, “This pest overwinters in the adult stage and becomes active at about the time that the earliest cucurbits are transplanted or seeded. It actively seeks out and moves into new cucurbit fields. Once in the field, it feeds for a period of time and the female will deposit her eggs in the soil at the base of the plants.
“The eggs hatch and the larvae feed on the cucurbit roots,” he continues. “The larvae complete feeding in several weeks and pupate in the soil. The next generation of adults emerge in early to mid-summer and the cycle continues.”
Although the larvae attack the roots, explains Bessin, the adults feed on all of the above ground portions of the plant including the stem, leaves, flowers, and fruits. He also cautions that heavy feeding damage by the adults can kill seedlings early in the season under extreme conditions. The late summer culprits, however, can damage and scar the rind of squash, pumpkins and smooth-skinned melons.
Signs Of Damage
As far as identification of damage in concerned, Bessin explains that the beetles have chewing mouthparts and remove tissue as they feed, so growers should see noticeable holes in leaves or small cavities in stems. A tattered appearance in the fruit or leaves is caused by callousing over of the feeding sites. This damage can cause the fruit to be unmarketable due to the production of lower quality fruit caused by the bacterial wilt the insect carries.
To combat issues like these, Bessin says that early scouting of the cucumber beetles should occur during the time when seedlings emerge or transplants are put in the ground. “For us it is not uncommon to see the beetles on the trays of transplants while they are still in the wagon,” he says.
Bessin does, however, say that despite all of the bad news, the silver lining is that growers have multiple options for control of the pest. “There are systematic treatments that can provide several weeks of control and are very effective against the overwintering adult generation,” he says.
There are also very effective foliar insecticides for cucumber beetles. “When using foliar sprays, growers also need to consider plant growth in that the vines can grow several inches in a day and that new growth may be unprotected,” adds Bessin.