Leucoma salicis
Pest description and crop damage Brownish caterpillars with white spots on back.
Management-chemical control
See:
Chemical Control of Nursery Pests
Spray in late summer when larvae are seen.
For more information
Johnson, W.T. and H.H. Lyon (1991), Insects That Feed on Trees and Shrubs, 2nd ed., Cornell University Press (p. 158).