Vegetable Program
Insect Management

Colorado Potato Beetle

Leptinotarsa decemlineata

Colorado potato beetles (CPB) are 1/2" long by 3/8" wide, oval with a rounded back, and each forewing is yellow with five black stripes. CPB overwinters in the adult stage, primarily in soil (up to 12 inches deep) in the woods and brushy borders next to host crops, though some burrow into soil in the field. In spring the beetles search for food plants by walking from the field edges. Heavy feeding may occur on edges on non-rotated fields. If beetles do not find host plants via walking they will fly in search of food.

In the Northeast, CPB survives on solanaceous crops and weeds, including horsenettle, nightshade, eggplant, potato and tomato (primarily seedlings). Once host plants are found adults feed, mate and lay clumps of 30-35 bright yellow eggs on the undersides of leaves. Eggs hatch in 7-10 days, depending on temperature. The larva is humpbacked, rusty-red with two rows of black dots along each side of its body. Feeding damage and larvae are easily seen on leaves. Larvae grow through four stages and reach 5/8" long before they drop to the soil and pupate. Because the last stage does 85% of the feeding damage it is critical to control larvae while they are small. Adults emerge from pupae after 10-14 days. In southern New England there is second generation of eggs, larvae and adults, while northern New England there is one generation.

Cultural controls. The single most important tactic for CPB management is to rotate potatoes, eggplant and tomato to a field that is at least 200 yards from the previous year’s fields. Barriers such as roads, rivers, woodlands, and fields with other crops are helpful. This single practice delays colonization and reduces population densities.

Mechanical barriers such as trench traps, trap crops and straw mulch also delay and reduce infestation. Install plastic-lined trench traps next to overwintering sites at least one week before adults emerge. Trenches should be 1' to 2' deep and 6" to 24" wide at the top. They can be U- or Vshaped with side walls sloping at angles between 65° and 90°. Beetles walking from field borders fall into the trench and cannot fly out. Perimeter trap crops may be potatoes
planted earlier than the main crop to attract beetles before the main crop emerges, or planted between overwintering sites and this season’s crop. Flame, vacuum or spray border crop before beetles move into the main crop. Another approach is to plant three to five rows of potatoes treated with a systemic insecticide in a perimeter around the field; this treated border will kill up to 80% of the colonizing beetles. Straw mulch around the host crop has been shown to reduce beetle numbers. Late planting may cause beetles to leave the field before potatoes emerge, resulting in lower beetle numbers.

Natural enemies that attack CPB eggs or larvae include twelve-spotted ladybeetle, spined soldier bug, a carabid beetle, Lebia grandis and a parasistic tachinid fly. Beauvaria bassiana has been shown to suppress beetle populations though it does not provide immediate control.

Colorado potato beetles rapidly develop resistance to insecticides.This can happen in as short a time as one year and is likely whenever a single class of insecticide is used multiple times against the same population in the same and succeeding years. The population on a single farm may develop resistance in response to management practices on that farm.

Wherever possible, growers should rotate classes of insecticides and avoid using the same chemistry more than once per year, or better, once every other year. Do not use the same chemical class on successive generations in the same year. There are enough different classes to allow this, if you plan carefully. Note the resistance group number of each insecticides and avoid using chemistries from the same group. Use newer chemistries first.

Do not try to kill every beetle in the field. Potato crops can withstand 15% defoliation without affecting yields. Avoid spraying the beetle in late season, as food reserves in the foliage two weeks prior to senescence add little to final tuber bulking.

Scout to determine whether or not a damaging population is present. When using products that control only larvae, scout for eggs, note egg hatch and apply controls before larvae reach third instar. For materials that control all stages, you may wait and scout for adults and larvae to determine the need to apply insecticides.

To use the threshold table below, walk the field in a Vshaped pattern and select 50 potato stalks at intervals, e.g., every 10 to 20 paces, depending on field size. Count adults, large larvae (greater than half-grown) and small larvae (less than half-grown) separately. If the number of CPB is high,
an insecticide should be applied; if the number is low, no insecticide is required for that week. If the number of CPB is between high and low, no insecticide should be applied, but the field should be checked in three to five days. Otherwise, the field should be checked weekly. These thresholds are for mid-season. Late in the season, potato plants can tolerate more defoliation without affecting yields.

Action Thresholds

                                                                                              No. of CPB per 50 stalks
Life Stage                                                                              Low                    High
Adults                                                                                  15 or fewer          25 or more
Small Larvae                                                                      75 or fewer         200 or more
Large Larvae                                                                      30 or fewer          75 or more

Colorado Potato Beetle, Leptinotarsa decemlineata, egg mass

For Current information on production methods (including varieties, spacing, seeding, and fertility), weed, disease, and insect management, please visit the New England Vegetable Management Guide website.

Below you will find additional information on managing this insect, including photos, fact sheets, articles, and power point presentations, when available.

Articles

• Managing Colorado Potato Beetle
• IPM Guidelines