1. Defoliation by cankerworms in 1979 was significantly less in 1978 treated shelterbelts than in untreated shelterbelts. 2. Most shelterbelts treated in 1978 retained enough foliage by late June 1979 so that adjacent crops were protected from wind. 3. Aerially applied Bt at a rate of 1/2 lb./acre provided shelterbelt foliage protection for 2 seasons. 4. The 3 gallon/acre Bt formulation appears to provide more consistent foliage protection than the 1 gallon/acre formulation.