Cucumber Beetle
By Jutta Thoerner UCCE Master Gardener
Western Spotted Cucumber Beetle
Diabrotica undecimpunctata
Region of county most prolific: all areas
Size: 1/5 inch long, 1/10 inch wide.
Season most prolific: spring, early summer
Bug environment: Adult beetles are found on leaves; grubs are in soil.
IPM: http://ipm.ucamr.edu/pmg/r116300511.html
Snapshot: The western spotted cucumber beetle shows itself with 12 black spots on a light green wing covers in the garden. This small beetle is a destructive pest than can kill young seedlings before the 3rd leaf stage and will cause considerable damage to adult plants through feeding on flowers and leaves. They also attack young melons and cucumbers, leaving scar- like marks. Adults will lay eggs at the base of non-host plants like grasses or corn in the soil. Eggs (laid in pale, orange-yellow clusters) will hatch after several weeks and larvae (3/8 inch and cream colored) will feed on plants roots and underground stems. It takes 40-60 days to develop from egg to adult. There is typically one generation per year. The adults prefer cucurbit plants like cucumber and squashes, but also feed on leaves and flowers of radish, mustard, lettuce, roses, beans, peppers and even tomatoes.
Non-pesticide options for reducing damage include the following. Use row covers until plants flower. Plant a trap crop of desirable plants close to the plants you want to protect. Options include radishes, mustards or Swiss chard. If high infestation occurs, low toxicity insecticides, such as neem oil, can be applied to the trap crop if you find more than 25% of a plant defoliated. Preventive measures for the following year include keeping the garden clean. Remove all leaf litter and weeds as these are potential hosts for adults. Monitor your garden in the spring, catch and destroy beetles as they emerge. Make it a game and challenge yourself to stay one step ahead.