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Colorado Potato Beetle

Closer Look Of The Colorado Potato BeetleLarge, stripped beetles, and their larvae, that feed on the leaves of tomatoes, potatoes, peppers and eggplants, chewing 1/8” holes, eventually defoliating the entire plant. It is by far the most destructive pest to the potato plant, and once your garden is infected it becomes increasingly difficult to eradicate the pest, due to its resistance to chemical insecticides. Commonly called simply ‘potato bugs’, they overwinter in the soil, usually near plants they attacked the previous year, and then reappear in spring. Common to eastern North America and Europe, they are considered a major pest, causing great damage to vegetable crops, especially those of small, home gardens, where they can wipe out the entire harvest. Feeding that occurs within two weeks of peak flowering (fruiting), especially on potato plants, will have a dramatic effect on yield. They got their name because the beetle was first thought to have derived in Colorado, but some say they appeared in Iowa and Missouri beforehand.

Adult

The Adult Colorado Potato BeetleThe adults are about 3/8ths inch long, usually bright yellow with about ten black strips on a convex back. It has black spots on its neck (thorax) and lives as an adult for about two weeks. They become active in May and will begin to lay eggs as soon as suitable plants are found. The second generation of adults normally appears in July and causes the most damage, due to the leafy vegetables. Begin checking for beetles in mid-May if you live in the upper Midwest, and continue to check until about August 1st.


Eggs

Colorado Potato Beetle EggsAdult beetles lay clumps of 20 to 40 eggs, normally orange-yellow in color, on the underside of leaves, usually in June, which hatch in 4 to 9 days later. Each female can lay 400 or more eggs over a four to five week period, so their numbers can grow quickly. Home gardeners should remember that eggs are not susceptible to insecticides, so do not ‘dust’ them with chemicals at this stage.


Larvae

Colorado Potato Beetle LarvaeThe larvae are normally orange/red in color, has six legs and is about 1/8 to 1/4 inch long. It has two rows of black spots running down the sides of its humpback body, topped by a dark head. They will feed on plant leaves for several weeks when they emerge in late spring, will then drop from the infected plant, burrow into the soil and pupate into adults. They will molt (shed their skin) about four times during their larvae stage, before pupating. Young larvae don’t cause that much damage, but during the later stages (instars) of their lives, they eat voraciously.


Pupate

Colorado Potato Beetle PupaWhen the larvae are mature, they form an underground earthen cell, enter the inactive pupae stage for one or two weeks, and emerge as adult potato beetles. The new adult female feeds for a few days before egg laying begins again, going from egg to adult in as little as 21 days. If your garden is covered with plastic, such as our own, it tends to cut down on the number of beetles that can get underground to pupate, thus reducing future infestations. Pupae cocoons are not susceptible to insecticides; so don’t spray them with chemicals.


Vegetables That Colorado Potato Beetles Like To Eat

Eggplant Peppers Potatoes Tomatoes

Control

Using floating row covers (see picture at left) will protect your young vegetable plants from the adult laying their eggs on or near your plants. (See Bill's Projects for making your own row cover supports) Set out white or yellow sticky traps to see how many beetles are in the area. Hand pick when possible or use a portable vacuum cleaner for small infestations. Be sure to wash your hands before touching your eyes or mouth due to a chemical on the beetles that can blister sensitive skin. Crop rotation will also confuse the beetles and will reduce their numbers.

The beetle has become immune to many of the common insecticides, including carbaryl (Sevin). And in some parts of the country, it has become immune to virtually all chemicals. However, one certain type of BT is said to be effective against young larvae, the San Diego formula (ordinarly BT, var. kurstaki, is effective against caterpillars, but has no effect on beetle larvae). If applied when the larvae are in their first or second instar (molting) phases, it causes a lethal infection and will quickly kill them. Remember that BT is harmless to humans and most beneficials and is generally approved by organic gardeners.

Rotenone will sometimes kill the pests, as well as neem-based insecticides. Azadirachtin is also said to be effective on some beetle populations. There are a few insecticides that are derived from bacterial toxins, but one that is available to the home gardener is a product from Bonide called ‘Colorado potato beetle beater’, although we have never used this and cannot vouch for its effectiveness. Other remedies that have been reported with some success are mix #1 and mix #13.


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