The name "leafroller" is given to several kinds of caterpillars that chew foliage and roll it around themselves, thus protecting themselves from predators such as birds. On many plants, they cause only minimal damage. However, leafrollers that feed on trees such as aspen, horsechestnut, maple, oak, poplar, and willow may do serious damage as they devour new growth; some trees may be completely defoliated.
Leafrollers have many natural enemies, including birds and trichogramma wasps. Bt may control young caterpillars when they are feeding heavily. Eggs are laid directly on trees; you may be able to smother them by spraying deciduous trees with horticultural oil during dormancy.
For chemical control, use acephate, carbaryl, or diazinon when caterpillars are feeding.