Colorado Potato Beetle
Garden pest · Leptinotarsa decemlineata
Description
The Colorado potato beetle is a leaf-eating beetle that attacks potatoes and other plants in the nightshade family, especially eggplants and sometimes tomatoes. Both adults and larvae feed on foliage. Small larvae make irregular holes; larger larvae and adults can consume most of a leaf, leaving its thicker veins. Heavy feeding can strip a young plant of leaves, slow its growth, and reduce the potato harvest. Adults spend winter in soil or sheltered places, then emerge in spring to feed and lay eggs on leaf undersides. Several generations may develop in a growing season, depending on the climate. Beetles can fly between gardens, so an infestation may appear even where potatoes were not grown the previous year. Check plants regularly: damage is much easier to manage while eggs and young larvae are still concentrated on a few leaves.
Symptoms
- Holes in leaves
- Insects visible on the plant
- Stunted growth
How to Identify
Adults are rounded, yellowish beetles about 10 mm (3/8 inch) long, with ten lengthwise black stripes across their wing covers. Their plump, hump-backed larvae are reddish-orange with rows of black spots along the sides. Look for clusters of yellow-orange eggs on leaf undersides, often alongside feeding damage. Young larvae make holes; older ones may leave only the larger leaf veins. Check for the insects before attributing holes to another pest. Striped cucumber beetles are smaller, have three black stripes across their backs, and chiefly feed on cucurbits. Lady beetle larvae, which are beneficial predators, are darker, flatter, and more spiny.
Prevention
Inspect potato and eggplant leaves, especially their undersides, at least twice a week during active growth. Remove egg clusters before they hatch. Rotate nightshade crops to a different part of the garden each year; placing them farther from last year’s planting helps because some beetles overwinter nearby. Floating row covers installed before beetles arrive can protect young plants, but seal the edges and avoid covering ground where beetles may already be emerging. Remove volunteers and nightshade-family weeds that can support the pest. Straw mulch may make it harder for emerging beetles to reach plants and can shelter predators. Keep plants adequately watered so they can tolerate limited feeding, but do not rely on plant vigor to prevent a heavy infestation.
Treatment
Start by hand-picking adults and larvae into soapy water and crushing or removing egg clusters from leaf undersides. Repeat every few days: newly hatched larvae are easier to control than large ones. On small plantings, removing heavily infested leaves can help if enough healthy foliage remains. If these measures are insufficient, a product containing Bacillus thuringiensis var. tenebrionis may control young larvae where available; it does not reliably control adults. Spinosad is another option for feeding larvae. Follow the product label for the crop, timing, coverage, and repeat applications. Avoid spraying open flowers or when bees are active. Insecticidal soaps can work on small larvae when sprayed directly but have little effect on eggs or adults. Use pesticides only when needed, and alternate labeled modes of action if repeated treatments are necessary: Colorado potato beetles can develop insecticide resistance.
Plants Affected
Not sure this is your problem? Try the problem diagnoser.