DEPOSITION CHARACTERISTICS OF AERIALLY APPLIED BACILLUS-THURINGIENSIS TO A HARDWOOD FOREST WITH HYDRAULIC NOZZLES

Deposit measurements (international units [IU] per cm2) were made on foliage after aerial application of Bacillus thuringiensis Berliner to hardwood forests. The quantities of spray arriving above each tree (collected by artificial collectors above the canopy) and between the canopies of individual trees in the same spray block were highly variable. Spray deposition in average upper and lower canopy strata and cardinal positions within each strata also were variable, but overall deposit was not significantly different. Deposits, averaged over plot, were 1.35 (+/- 0.07) and 1.26 (+/- 0.11) log IU per cm2 for the upper and lower canopy, respectively. The rank order of deposits changed among strata and positions within strata such that no consistent pattern of deposition could be found between trees. However, because the upper canopy contained a greater foliage area, more B. thuringiensis was caught in the upper canopy (3.70 x 10(7) IU per tree) compared with the lower canopy (2.03 x 10(7) IU per tree). Overall recovery of the spray applied was 55.2% on the foliage and 6.0% at the ground level. Spray that was not accounted for was probably either deposited on the trunk and branches or drifted from the spray plot. Distribution of deposit between individual leaves closely conformed to a log-normal distribution.