Problem type: Insect
Name of problem: Colorado Potato Beetle
Plant name(s): Potato, tomato, eggplant, weeds (ground-cherry, thistle)
Symptoms / Characteristics:
Adults and larvae feed on leaves, chewing irregular holes in leaves. Stems may also be attacked. High populations can completely defoliate plants. Extensive feeding, especially when the crop is in bloom can reduce yield.
Adults are fairly large, and have black and yellow stripes on their wings. Eggs are yellow-orange in color and are found in masses on the underside of leaves. Larvae are orange-red with two rows of dark spots along either side of their bodies. They are fat and soft-bodied with a humped-back appearance.
Adult beetles overwinter in the soil where the previous year's potato crop grew. They emerge in the spring (usually late May), searching for host plants on which to lay their eggs. One female can lay 300-500 eggs from June-July. Preferred host plants such as potatoes usually have not yet emerged from the soil surface when adults are emerging, so the beetles will resort to other plants such as weeds to lay eggs and to feed upon. Once potato plants become available, they will leave the weed plant for the potato or other desirable host plant.
Eggs hatch in about one week and larvae begin to feed on leaves throughout June. Larvae mature in 2-4 weeks, than drop to the ground to pupate. Adults emerge in 2-3 weeks. In most regions in Canada, unfavorable environments usually prevent adults from laying more eggs, but rather the adult beetles feed and get ready to overwinter. Generally there is one generation per year, but if conditions are right, there may be two.
Control / Preventions:
Monitor potato plants early. Adults and larvae can easily be seen. Physically removing adults, larvae or egg masses can be done if numbers are not too high. Another method of control is crop rotation. Avoid planting host plants in fields where beetles were present at the end of last year's growing season.
The potato beetle can be controlled by native predators including, the spotted lady beetle, ground beetles and the two-spotted stink bug.
There are a number of insecticides available for control but resistance has been reported on a number of products. Alternating the use of insecticides should be done using different chemical groups for control. Foliar sprays can be applied to control adults in the early season or at the end of the season when high numbers of adults are present. Spraying larval stages can also be done during blooming where numbers are high.