Quantity of deposit and droplet size spectra of two formulations of fenitrothion were compared at ground level and in conifer tree canopies, A new low-volatile, hygroscopic formulation, fenitrothion mixed with Dowanol® TPM, and a moderate-volatile formulation, fenitrothion mixed with Cyclosol® 63 and stove oil, were both sprayed at 210 g Al/ha with an aircraft equipped with six Micronair® AU4000 atomizers. The hygroscopic formulation was sprayed at 0.4 L/ha and the other at 1.5 L/ha, Kromekote® cards and glass plates were used to sample ground deposits and live balsam fir, Abies balsamea (L.) Mill., foliage and metal simulators were used to assess deposit in the tree canopy.
All measures of deposition on the ground, and on fir needles and foliar simulators in the canopy, were greater for the formulation sprayed at 1.5 L/ha than for the formulation sprayed at 0.4 L/ha. However, the difference was the smallest when measured in ug of AI/cm2. Deposits for both formulations were greater at ground level than those in the canopy. Deposit levels on metal foliar simulators were two to four times greater than those on living foliage with little variation of foliar deposit within branch tips without overhead obstruction. The hygroscopic formulation provided adequate deposit and has some potential for forestry applications. Metal foliar simulators are suitable samplers of spray deposit because they provide a sampling surface which would be constant from treatment to treatment and year to year.