You can protect precious nightshade vegetables from Colorado potato beetles by learning how to attract beneficial insects to your organic garden, and by utilizing crop rotation and floating row covers.
This article is part of our Organic Pest Control Series, which includes articles on attracting beneficial insects, controlling specific garden pests, and using organic pesticides.
The most common problem encountered when growing potatoes, Colorado potato beetle adults and larvae feed on the leaves and blossoms of potatoes, and may also be seen on eggplant, tomatoes or peppers. Badly hit plants produce poorly because so many leaves are consumed. Organic controls for Colorado potato beetles include crop rotation, mulching with straw, handpicking and maintaining good insect balance in the garden so that a wide variety of natural predators are present. Plastic-lined trenches can capture potato beetles before they find plants. Many populations of Colorado potato beetles are resistant to most pesticides, so organic methods should always be used when growing potatoes.
Native to the American Southwest, Colorado potato beetles are now found wherever potatoes are grown. Emerging in mid to late spring, just as potatoes begin growing vigorously, Colorado potato beetle adults are striking yellow-and-black striped beetles with black dots on their orange heads. Adults are often seen lurking in potato foliage, looking for mates. Much more visible are the reddish, soft-bodied larvae that appear a few weeks later, often clustered near the tips of growing branches. As they grow, the larvae develop a row of black dots down each side. When feeding on eggplant, the larvae may be gray in color rather than red.
Colorado potato beetle larvae are leaf-eating machines. If growing potato plants have developed flower buds by the time the larvae settle in to feed, they may migrate to the buds and consume them overnight. In the worst uncontrolled cases, Colorado potato beetles can completely strip plants of all foliage. However, in diversified organic gardens, this pest is more likely to appear in sporadic clusters on individual plants, because many of its natural predators consume eggs and young larvae. Where plenty of lady beetles, ground beetles and small wasps are present, only the best-hidden clusters of orange eggs survive.
In late summer, Colorado potato beetles fly to nearby wooded areas and overwinter beneath bark or other cover. In mid-spring, they emerge and walk until they find potatoes or another suitable host plant. After a little light feeding, mated females lay clusters of orange eggs on leaf undersides. The eggs hatch about two weeks later, and the larvae feed for a couple of weeks before entering their pupal stage. In cool weather the entire life cycle can take 45 days or more, but 30 days is more typical. This means that a second generation can emerge at the perfect time to sabotage midseason potatoes.
Numerous natural predators can assist in the struggle to manage Colorado potato beetles. These include lady beetles, toads, birds, predatory stink bugs, ground beetles, and several species of tiny parasitic wasps. In addition, foraging chickens and ducks have a long history of success as potato beetle predators.
Planting plenty of flowers that attract beneficial insects is a sound strategy, along with maintaining seldom-disturbed islands that provide habitat for ground beetles. Try to tolerate small outbreaks of aphids in early spring in order to provide food for ladybeetles.
Also consider these organic controls for Colorado potato beetles, listed in seasonal order.
Keep a close watch on your growing potatoes in spring, and do not allow the first generation to triple itself by the time your potatoes grow into big, robust plants. Any mulch with a straw-like texture, including coarse grass clippings, can keep populations low. Always rotate crops, and try to plant potatoes after a grain. Do all you can to provide food and habitat for beneficial wasps, flies, ladybeetles, and predatory stink bugs. Scout for eggs if adults are seen, using a small hand-held mirror to get a good look at leaf undersides.