The fall cankerworm is a native pest to the deciduous forest and ornamental trees of North America, including Apple, Ash, Cherry, Elm, Honeylocust, Linden, Maple, Red and White Oak, and many more trees and shrubs.
Common throughout most of North America.
- The common name of this species comes from the time of year when the adult moths appear, not when the larvae are present. It is also called inchworms, loopers, or spanworms.
- Cankerworms are caterpillars that move with a looping motion. Small numbers are present every year, but occasionally outbreaks occur and can cause significant defoliation of a variety of trees.
- This species of moths has slender, dull grey-brown bodies and large, broad forewings. Males are about one inch long, while wingless females are about a 1/4 inch long.
- Fall cankerworm eggs are laid in neat flat rows that encircle small stems and twigs. Individual eggs are barrel-shaped and shiny gray.
- Larvae range from light to dark green or light brown to black. Usually, they have three small stripes on either side of the abdomen.
- They are about an inch long when fully grown. Cankerworms have a distinct appearance and movement because they have fewer legs along the abdomen than do typical caterpillars. Most cankerworms have five pairs of abdominal legs, while the fall cankerworm has three pairs.
- Fall cankerworms complete their life cycle in four distinct phases: egg, larvae, pupae, and adult.
- They emerge as adult moths in late fall. The females crawl up tree trunks onto branches to mate with the winged males and then lay single‑layered masses of flower-pot-shaped eggs on limbs and trunks. The eggs are in the overwintering life stage.
- The eggs hatch in early spring, and females lay approximately 50 eggs. Larvae feed on foliage for 3 to 6 weeks. Then they crawl down the trunk or drop by silk threads to the ground. Once on the ground, they burrow into the soil, spin a cocoon and pupate.
- Fall cankerworm moths emerge in the fall
- Cankerworms have one generation per year.
Damage and Detection
- Newly hatched larvae eat the young leaves as well as the buds of numerous deciduous trees, including apple trees.
- Larger larvae eat all but the midribs or tougher veins of mature leaves.
- Most damage occurs about the time the leaves become fully developed and can include tattered leaves with random holes and fully chewed areas of foliage.
- In an infestation, trees may be completely stripped of foliage. Death is likely if the trees have been defoliated more than once or are in a weakened state.
Prevention and Control
Cankerworm females need to climb up tree trunks to lay their eggs. Barriers in the form of a band of sticky adhesive 5-6" wide around tree trunks can capture the female adults as they make their way up to lay eggs.
- Using insecticides for cankerworm control is not recommended. However, it may be required in certain circumstances, as continued defoliation can have long-term damaging effects on trees.
- To treat larvae, an effective organic option is a product containing Bt (Bacillus thuringiensis). It must be applied while larvae are still less than 1/2-inch long.
Robb Hannawacker, Flickr
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