Ultra-low volume aerial applications of Bacillus thuringiensis variety kurstaki for control of peach twig borer in almonds trees
Roltsch, W.J. | Zalom, F.G. | Barry, J.W. | Kirfman, G.W. | Edstrom, J.P.
This study describes the first known commercial use of an ultra-low volume (ULV), Bacillus thuringiensis (Bt) application on an orchard in California and compares different methods used to sample deposition of Bt within the canopy and orchard floor during prebloom and bloomtime applications. Early spring ULV application of Bt was studied to assess spray distribution and efficacy against the peach twig borer (Anarsia lineatella). A 16.7 ha (41.3 acre) almond orchard was divided into four blocks. Two blocks received an aerial application of Bt; the other two blocks served as untreated checks. Kromekote cards and polyethylene soda straws were located in tree canopies, and Kromekote cards were located on the ground to monitor spray droplet distribution. Plate cultures of Bt from twig samples were also made to evaluate deposition in the canopy. A rapid decline in droplet densities caused by drift during application occurred in control plot trees as distance increased from treatment plots. Within-tree, spray droplet densities varied considerably among canopy regions, and even on a small spatial scale within a given canopy region. Mean droplet densities were generally greater in the upper portion of the canopy. However, densities varied considerably from February (prebloom) to March (bloomtime) applications relative to upper tree and ground level locations. Mean droplet densities were far more consistent at mid-canopy locations. The ULV application of Bt by aircraft shows promise as an alternative to conventional chemical insecticides in controlling peach twig borer. A trend of reduced peach twig borer damage was noted under these conditions.
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