Q.: Each year, my potatoes are overrun with beetles. What can I do to prevent this?
A: It sounds like you have a problem with the Colorado potato beetle (Leptinotarsa decemlineata). This pest favors potatoes, but it also feasts on tomatoes, eggplants, peppers, and petunias. The beetle and its larvae don't actually go after the tubers. Instead they feast on the plants' leaves and shoots, inhibiting their ability to photosynthesize and reducing potato yields. Adults are yellowish orange with black spots behind their heads and 10 black stripes on their wing covers. They overwinter in the soil and emerge in late spring and walk to host plants, where they lay clusters of yellow, oval-shaped eggs. The larvae hatch and feed for up to 3 weeks before they pupate in the soil. There may be as many as three generations per year in the South, while farther north, one to two generations is typical.
The easiest and best way to prevent damage to your potato crop is to create a barrier between the pest and the plants with a lightweight floating row cover. Place the row cover over the potatoes after planting and leave it on until you are ready to harvest.
If you don't use a row cover, regularly inspect your plants and destroy egg clusters, larvae, and adults. Place a heavy layer of straw mulch around your potato plants. Research indicates that the mulch inhibits the Colorado potato beetle's ability to actually find your potatoes, and the mulch acts as a microenvironment that encourages the beetle's natural predators, including ground beetles, which feed on larvae, and lady beetles and lacewings, which feed on eggs and larvae.
Plant coriander, dill, sweet alyssum, fennel, and cosmos around your potato patch to attract the beneficial insects. Also try planting potato varieties that mature before pest populations reach their height in early summer, such as 'Caribe', 'Superior', and 'Yukon Gold'.
Surrounding your potato patch with a plastic-lined, V-shaped trench can also reduce the number of adults that reach your plants in spring. As they emerge from the soil and head for the plants, they fall into the trench and can't get out. Destroy them.