Click beetles were formerly considered to be important pests of grapes in B.C., but extensive study in Okanagan vineyards over a number of years has shown that most of the damage formerly attributed to click beetle adults was in fact caused by half grown cutworm larvae.
Several species will feed occasionally on buds of grapes, but control is usually not warranted. Click beetles are also not considered pests of grape in Washington state.
Click beetle larvae, called wireworms, have long, slender, hard bodies that are a light tan to a light orange-brown in colour and appear somewhat shiny and polished. Their short legs and cylindrical slender bodies allow them to burrow through the soil to feed on the roots of plants.
Adult beetles have elongate, somewhat flattened bodies usually in shades of brown or black. The segment behind the head has small projections that point backward on each side of the body. Adults of most species are 1-1.5 cm in length, but some are significantly larger.
When adults are placed upside down in the palm of a hand or gently held between finger and thumb, they will rapidly flex their bodies at both ends and attempt to right themselves or escape with a characteristic clicking action.
Adults that spend the winter under debris and leaves emerge with the arrival of warm weather in spring to feed on the tender buds and leaves of a wide range of plants, occasionally including grapes. They are often quite common on flowers where they feed on soft tissues and pollen.
After feeding for a short time, females begin to deposit eggs into the soil. In two or three weeks, the eggs hatch into larvae resembling small slender worms that develop in the soil throughout the summer.
Click beetles can persist for a long time without feeding, and they often require more than one year to complete development to the adult stage.
Larvae are not known to damage the roots of grapes to any extent, preferring to feed on the roots of weeds or grasses.
Click beetle adults are often seen feeding on sap from pruning cuts. As with cutworm larvae, feeding of click beetle adults causes death of developing buds, reduced yields and delayed and uneven ripening of fruit. Little damage occurs after bud break.
Adult click beetles feed on buds so infrequently that monitoring for these pests is generally not warranted. The presence of adult click beetles in a vineyard does not indicate feeding or correlate with damage.
There are no established thresholds in B.C. relating click beetle numbers to bud damage. To determine if bud damage is due to click beetles or cutworm larvae, it is best to inspect vines with the aid of a flashlight after dark on warm spring nights.
Chemical control of click beetles is generally not warranted and none are registered specifically for adults on bearing vines. Sprays for cutworm larvae should help control adult click beetle.
Little information is available on the biological control of click beetles in B.C. vineyards.
As with climbing cutworm, the presence of broadleaf weeds in spring helps reduce click beetle damage to grapes.
