Forest Tent Caterpillars Affect Sugar Maple Health

Feeding by forest tent caterpillar caused widespread defoliation of sugar maples in 2005. Many areas have been defoliated for several years in a row. Some forests also had high levels of lecanium scale causing additional tree stress. Long-term tree health problems may result.

Forest tent caterpillar defoliation was mapped on 484,081 acres of forests in 12 counties (see map). The most extensive damage occurred in Rutland, Bennington, Windsor and Windham Counties. Historically, outbreaks last 1-3 years in one region, but 3-8 years statewide, as new regions are defoliated.

Defoliation affects tree health by reducing starch reserves available for winter survival, sap production, spring leaf flush, and wood growth (needed for taphole closure).  Trees growing on nutrient rich soils are better able to tolerate defoliation. Healthy hardwood trees can usually withstand several consecutive years of defoliation but with each additional year, the risk of dieback and some mortality increases, particularly if other stressors are present.

Forests managed for maple syrup production tend to have a higher proportion of sugar maple trees than natural stands and therefore may experience more serious defoliation. Sugarbush operators in affected regions should take precautions to prevent tree decline and mortality following this defoliation event.

VT Dept. Forests, Parks & Recreation, October 2005

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