THE EFFECTS OF APPLICATION RATE AND SPRAY VOLUME ON EFFICACY OF 2 FORMULATIONS OF BACILLUS-THURINGIENSIS BERLINER VAR KURSTAKI AGAINST CHORISTONEURA-ROSACEANA (HARRIS) (LEPIDOPTERA, TORTRICIDAE) ON RASPBERRIES

The relative toxicities of two formulations (Dipel WP and Foray 48B) o f Bacillus thuringiensis Berliner var. kurstaki to the obliquebanded l eafroller, Choristoneura rosaceana (Harris), were determined in the la boratory. The effects of application rate (BIU per hectare) and spray volume (litres per hectare) on the efficacy of Dipel WP and Foray 48B against C. rosaceana were determined in raspberry fields. Mortality of C. rosaceana increased with application rate, and decreased with an i ncrease in spray volume. Bacillus thuringiensis exhibited significantl y longer residual activity at higher application rates and at lower sp ray volumes. The half-life (time at which 50% of original activity rem ains) of B. thuringiensis ranged from 2.45 to 6.68 days, depending upo n application rate and spray volume. Laboratory and field studies indi cate that Dipel WP and Foray 48B are highly and equally effective in k illing larvae of C. rosaceana.