While weeding your garden in mid June, you find some reddish larvae chewing on the leaves of your potatoes.
1. What are these insects?
They are the larvae of Colorado potato beetles. They range in color from brick red (when they're young) to pinkish (when they are older) and have 2 rows of blacks spots running down their back. They are also humpbacked in shape. In addition to potatoes, they also can feed on tomatoes, peppers, eggplants and other plants in the nightshade family.
2. How long will they be in your garden?
Individual larvae can develop into the familiar adult potato beetles as fast as 10 days. However, these beetles usually go through two generations each year. And the generations usually overlap so you can find larvae throughout most of the summer.
3. How damaging are these insects to potatoes?
Colorado potato beetles can potentially defoliate an entire plant. Both larvae and adults feed on potatoes, however old larvae by themselves cause as much as 75% of all of the feeding damage. Potatoes can usually tolerate up to 30% defoliation earlier in the season. But when the tubers begin to bulk (soon after flowering), potatoes can only tolerate about 10% defoliation.
4. How can I get rid of them?
Keep plants healthy, especially by keeping them well-watered. Healthy plants are more tolerant to feeding damage. You can handpick small numbers of Colorado potato beetles. Just knock them off into a pail of soapy water. If you have larger numbers of insects present, spray them with a bacterial insecticide, Bacillus thuringiensis var. tenebrionis. This product is very low in toxicity and Colorado potato beetles have not developed resistance to it (as is the case with virtually all other garden insecticides). However, this product is not effective against adults and older larvae. The best way to use this insecticide is to apply it against eggs or newly emerged larvae. Reapply it every three or four days to maximize its effectiveness.
