Cucumber Beetles

Cucumber beetles are major pests of cucumbers, melons, squash, and other cucurbits

Spotted cucumber beetle (Pollinator) CC BY 2.5

There are three major classes of cucumber beetle that I know of: spotted, striped, and banded. Banded cucumber beetles are mostly found in southern regions, while striped and spotted cucumber beetles begin emerging in late spring and can have as many as three generations in a single season in some warmer regions.

Striped cucumber beetle (Scott Bauer) Public Domain

Cucumber beetle identification
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Cucumber beetles are relatively easy to identify. They are small, only one-quarter of an inch long, and they have shiny black heads. The larvae are yellowish with a dark head. Other identifying marks, by species, include:

• Western spotted cucumber beetle (Diabrotica undecimpunctata undecimpunctata) - adult beetles are bright greenish-yellow with 12 black spots. They are sometimes confused with ladybugs, but ladybugs have short, stubby antennae, while cucumber beetles have thin antennae that can be up to 1/4 inch long.
• Western striped cucumber beetle (Acalymma trivittatum) - three black stripes and an orange thorax (these are seen less often in San Jose, California)
• Banded cucumber beetle (Diabrotica balteata) - rarely seen outside of the southern U.S. regions

Banded cucumber beetle (Russ Ottens) CC BY 3.0

Cucumber beetle damage

Adult beetles overwinter in the soil and lay their bright orange eggs at the base of host plants. When these eggs hatch, ravenous larvae start feeding on plant roots. Adults will feed on roots, blossoms, leaves, and plant crowns, along with fruit, as they feed. This is especially true for tender, new growth. Cucumber beetles can easily kill seedlings, and they feed on far more than just your cucumbers. Other favorite plants are corn, beans, lentils, roses, and grasses, along with your melon and squash plants. They are also attracted to ripening stone fruit. Holes in leaves may be the first obvious sign of infestation. Cucumber beetles can also carry squash mosaic virus (for up to 20 days after feeding on infected fruit), and bacterial wilt, a fatal cucurbit disease.

Winter squash blossom damaged by striped cucumber beetle feeding (RFMitchell) CC BY-SA 3.0

Controlling cucumber beetles

Cucumber beetles are difficult to control. Parasitic tachinid wasps provide some assistance, so avoid broad spectrum pesticides, which will kill off your helpers along with the pests. Cucumber beetles prefer cool, moist places, such as under your squash or melon plants after they have been watered. That makes it the best time to look for these pests and squish them as soon as you see them. They can bite, so wearing gloves is a good idea. Since cucumber beetles can fly, battling them is an ongoing process. Regular monitoring is your best defense.