Drums of Bacillus thuringiensis (Bt) formulation are sampled to check the viable spore concentration. Corvallis, Oregon.
Photo by: Wally C. Guy Date: November 1963
Credit: USDA Forest Service, Pacific Northwest Region, State and Private Forestry, Forest Health Protection. Collection: Portland Station Collection; La Grande, Oregon Image: PS-2852
For additional information see: archive.org/details/CAT92272778 Carolin, V.M. and C.G. Thompson. 1967. Field testing Bacillus thuringiensis for control of western hemlock looper. Research Paper PNW-38. Portland, OR: USDA Forest Service, Pacific Northwest Forest and Range Experiment Station. 26 p.