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Dipel® 8AF was sprayed aerially over an oak forest (Study I, conducted in Ontario, Canada, in 1987) undiluted at 30 BIU in 1.8 L/ha on block B1 and diluted at 30 BIU in 6.2L/ha on block B2. Spray drops were collected on cylindrical Kromekote® cards, and deposit was determined on aluminum oak leaves by fluorometry for the tracer dye added to the tank mixes. The data showed that the drop sizes on samplers were markedly smaller in block B1 than those in B2. The deposits (expressed in IU/cm2) at canopy and ground levels were correspondingly lower in B1 than in B2.
Foray® 48B was sprayed aerially over an oak forest (Study II, conducted in Pennsylvania, USA, in 1990) undiluted at 50 BIU in 3.94 L/ha on block B3 and at 75 BIU in 5.91 L/ha on block B4. Drop spectra were assessed on water-sensitive paper, and deposits were determined on glass micro-fiber filters by a bioassay method using gypsymoth. The observed mortalities were converted into IU of deposit/cm2 area of the filters. The data indicated that drop sizes on samplers were only slightly smaller in block B3 than those in B4. The deposits were also not markedly different.
When converted into IU/cm2 per BIU sprayed, the deposits were: Study I Ground level: B1, 1.3 IU/BIU-cm2; B2, 3.0 IU/BlU-cm2 Canopy level: B1, 1.5 IU/BIU-cm2; B2, 3.7 IU/BIU-cm2 Study II Ground level: B3, 1.7 IU/BIU-cm2; B4, 0.68 IU/BIU-cm2 Canopy level: B3, 1.3 IU/BIU-cm2 ; B4, 0.75 IU/BIU-cm2
The conclusion was that the differences in deposits in the two studies were not as enormous as might be expected, considering the fact that the studies were conducted under different field conditions, and using different dosages, volume rates, samplers and quantification techniques for deposit assessment.
Dipel® 8AF, Foray® 48B, volume rate of application, drop size spectra, initial deposits, artificial samplers
Research Scientist and Project Leader, Pesticide Formulations Project at Forestry Canada, Forest Pest Management Institute, Sault Ste. Marie, Ontario