Spring cankerworm, Paleacrita vernata, and fall cankerworm Alsophila pometaria, often called inchworms because of the way they crawl, feed on buds and expanding leaves in the spring. The larvae’s droppings can also be a nuisance. Low populations of cankerworms do not cause extensive damage. However, high populations, such as we experience here in the Charlotte Metro Area, can defoliate trees by late spring. Multiple years of defoliation can negatively affect the health an already stressed tree. The feeding habits and damage are very similar for the spring and fall cankerworm, but the life cycles are different.
Cankerworm control is not always needed. Healthy trees can withstand extensive defoliation since cankerworm damage is done early in the spring and trees have the chance to leaf out again. Control is recommended for new transplants and high valued specimen trees. Trees that have a previous history of stress such as defoliation, drought, or disease should also be treated.
Chemical treatment is most effective from caterpillar emergence through the second week of feeding after egg hatch. Damage is minimal and caterpillars are still small at this time, so close inspection is needed. During the third and fourth weeks after egg hatch, cankerworm damage becomes extensive and very noticeable. Treatment is not effective at this time because the damage is already done.
Consider Mectinite or Lepitect Infusible as tree injection treatments for trees that cannot be treated with foliar sprays or other systemic options
Other Treatment Practices
- Applying ‘sticky’ bands to the trunks of trees later fall through early winter will capture female moths as they climb the tree.
Soil injections of Lepitect will begin efficacy within 3-10 days for most pests. Control on larger trees will not occur as quickly (2-3 weeks). Lepitect soil applications last for 30 days after treatment. Repeat applications may be necessary if pest activity persists for longer than 30 days.
Signs of Damage
- Small holes on leaves in spring are caused by young larvae
- Complete defoliation, except for the leaf veins, may occur by late spring by older larvae
- The spring and fall cankerworm are very similar in appearance; they are often called inchworms because of the way they crawl
- They arch their back into a loop and extend the front to move forward
Photo: Patrick Anderson
Photo: USDA Forest Service – Ogden Archive
USDA Forest Service, Bugwood.org
Photo: Female cankerworm and eggs
Patrick Anderson, Rainbow Ecoscience
Trees At Risk
Cankerworms have a wide host range, but prefer willow oak (Quercus phellos), maple (Acer), dogwood (Cornus), and cherry (Prunus). Crabapples are also a preferred host.
- Adult moths emerge from the soil in fall after a hard freeze, usually between Late November and January.
- Mating occurs as the females search for small twigs to deposit her eggs on. Both males and females die after the eggs are deposited.
- Eggs hatch in early-spring at about the same time as the opening of willow oak buds (148-290).
- Larvae feed on leaves for about four weeks before dropping to the ground to pupate in the soil where they will emerge later in the season as adults.
- Adult moths emerge in early spring.
- Eggs hatch in mid-spring at about the same time as the opening of willow oak buds (148-290).
- Larvae feed on leaves for about four weeks before dropping to the ground to pupate in the soil where they will emerge the next spring as adults.
University of KY
Johnson, W.T., Lyon, H.H. 1991. Insects That Feed On Trees and Shrubs.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.