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Protect Potato Yields by Managing Colorado Potato Beetles

Colorado potato beetles are perhaps the most common and potentially destructive potato pest in the U.S.

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Updated:

June 4, 2024

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Figure 1: 4th instar Colorado potato beetle larvae are responsible for 75% of the defoliation observed on potato plants. Photo by Thomas Ford, Penn State Extension.

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If left unchecked, these leaf-feeding beetles can completely defoliate potato vines in a matter of days. The adult Colorado beetle has an oval body with black, narrow stripes on the wing covers (elytra). To overwinter, Colorado potato beetle adults burrow deep in the soil in recently cropped potato fields, hedgerows, or forested sites. In late April to early May, adult Colorado potato beetles will emerge from the soil and migrate to potato fields to feed and lay clusters of bright yellow eggs on the lower leaf surfaces. A single adult female Colorado potato beetle can lay up to 350 eggs in her lifetime.

Colorado potato beetle egg hatch can vary according to temperature. Entomologists note that egg hatch can occur in as little as 3–4 days under warm temperatures (84°F) or as long as 16 days under cooler temperatures (60°F). After hatching, Colorado potato beetle larvae will go through 4 larval stages. The first instar of the Colorado potato beetle appears hump-backed and brick red in color, but subsequent instars will appear light orange to tan in coloration. Colorado potato beetle larvae also have blackheads and black legs with two rows of black spots along both sides of the larva's body.

When larvae mature, they drop to the ground and will burrow 3–6 inches into the soil to pupate for 2–3 weeks before emerging as adults. Upon emerging from the soil, adult Colorado potato beetles will begin feeding aggressively on the potato foliage before initiating a new round of egg-laying. Potato growers may observe two complete generations a year in the Mid-Atlantic region. In the south (NC), growers may observe as many as 3–4 generations of Colorado potato beetles per year.

Management of the Colorado potato beetle begins with crop rotation. Crop rotation often delays potato infestation while reducing pest pressure. Potato plants can tolerate up to 20–30% defoliation prior to flowering, 5–10% defoliation after flowering, and 30% defoliation at tuber formation before a reduction in yield is observed.

Vegetable entomologists recommend that foliar insecticides be applied to potato foliage when 15-30% of the eggs hatch for the best control. Treatment of 4th-instar larvae is particularly ill-advised since mature larvae are more difficult to kill, and 4th-instar larvae are responsible for 75% of the defoliation observed by growers.

Pesticide resistance is frequently observed in Colorado potato beetle populations. In areas where two complete generations of Colorado potato beetles are seen, pesticide resistance may occur in 3–5 years. Potato growers should rotate insecticides with different modes of action to lessen the risk of pesticide resistance developing on the farm. Avoid late-season insecticide applications to prevent the build-up of insecticide resistance in overwintering Colorado potato beetle adults.

Potato growers should not rely exclusively on the neonicotinoid class (Group 4A) of insecticides for Colorado potato beetle management. Foliar applications of neonicotinoid insecticides in potatoes should not be used in fields that have been previously treated with neonicotinoid seed treatments or at-planting neonicotinoid treatments. Research from Tom Kuhar's lab on the Eastern Shore in Virginia shows approximately 50 days of control from a neonicotinoid product (Group 4A), and a little longer from a diamide (Group 28).

Growers should begin scouting their potato fields at plant emergence. Growers or scouts should sample fields weekly for Colorado potato beetle to determine if insecticide treatment is required. When scouting potato fields, selecting 10 sites per field is recommended, and using a V or W-shaped path through the field to scout. At each site, choose one potato stem from each of 5 plant adjacent plants and count and record all adults, large larvae, and small larvae. If more than 50 adults, 75 large larvae, or 200 small larvae are counted per 50 stems, insecticide treatment is recommended.

Some of the insecticides listed below may not be effective for controlling Colorado potato beetles in certain areas of the Mid-Atlantic region due to insecticide resistance concerns in some populations.

Insecticides labeled for postemergence application for Colorado beetle management in the Mid-Atlantic Commercial Vegetable Recommendations include: