Results of spraying Bacillusthuringiensis 2 consecutive years over balsam fir stands damaged by spruce budworm

Abstract

In 1977 and 1978, seven 40-ha blocks mostly composed of balsam fir (Abiesbalsamea (L.) Mill.) were treated with combinations of Bacillusthuringiensis formulations of three bacillus concentrates, from different producers, and two carriers, sorbitol and sodium dihydrogen phosphate. Proper calibration of the boom and nozzle spray system of a Grumman Ag Cat aircraft ensured sufficient and homogeneous dispersion of the bacillus. Larval mortality and tree defoliation observed varied according to the foliage potential and population levels before treatment. In treated blocks, current-year growth defoliation varied between 35.5 and 99.5%, and between 7.4 and 47.1% in 1977 and 1978, respectively. In untreated blocks, it varied between 94.8 and 100%, and between 81.8 and 100% in 1977 and 1978, respectively. In 1977, in treated blocks, foliage potential of balsam fir showed a 31.5 to 100% increase while in untreated blocks a 10.5 to 47.0% decrease was noted. In 1978, in treated blocks much of the current-year growth was preserved and 100% foliage potential was reestablished.