Spring cankerworm

The spring cankerworm (genus Paleacrita), specifically Paleacrita vernata, is a significant defoliating pest belonging to the order Lepidoptera, family Geometridae. This moth is infamous for its ability to cause massive canopy damage in urban forests and commercial orchards throughout North America.

The host range is extensive, primarily focusing on broad-leaved trees. Preferred hosts include American elm, oak, maple, and various fruit trees such as apple and cherry. In instances of high population density, the larvae can consume the entire foliage of a mature tree in a matter of weeks.

The biological cycle is unique due to the flightless females, which must crawl up tree trunks to deposit egg masses in bark crevices. The larvae, often called 'inchworms' due to their characteristic looping gait, hatch in early spring synchronously with leaf expansion. After feeding, they drop to the ground to pupate in the soil for the remainder of the season.

Damage occurs in early spring when the larvae feed on expanding buds and leaves. Initial symptoms appear as small, irregular holes in the foliage, progressing to complete skeletonization. This heavy defoliation stresses the trees, reducing their ability to store carbohydrates and making them vulnerable to secondary pathogens or drought.

Effective management requires proactive monitoring and intervention:

• Applying sticky or tanglefoot barriers on tree trunks during late winter to trap climbing females.
• Monitoring for egg masses and early larval emergence to determine the need for control.
• Using biological controls like Bacillus thuringiensis (Bt) to specifically target larvae while sparing beneficial insects.
• Implementing systemic soil injections or foliage sprays with insecticides when infestation levels exceed economic thresholds.