"The Influence of Dormant Spray Oil on Diazinon Deposition and Transfer to Non-Target Vegetation" Environmental Monitoring and Pest Management Division

In a 1989 study, the California Department of Food and Agriculture (CDFA) determined that organophosphate pesticides used in orchard dormant spraying were being deposited on non-target row crops grown at distances less than and greater than 0.4 km from the site of pesticide application. The residues found on non-targeted crops may have been the result of drift during pesticide application or transport of pesticide in vapor or particulate phase from branch and soil surfaces after application. A field experiment was designed to determine if applying dormant spray oil in conjunction with diazinon affects mass deposition on branch surfaces. An increase in deposition on branch and s o i l surfaces would indicate a reduced mass available for off-site drift during an application. Experimental structures to which real and surrogate branches were attached were used to compare deposition rates between oil and non-oil applications. Fallout cards placed beneath the structures measured soil deposition. Statistical results indicated that dormant spray oil had no effect on the deposition of diazinon on branch or soil surfaces. However, the lack of difference between treatments may not be definitive because of differences in tank sample data. Deposition on surrogate branches was significantly different from that on real branches, limiting the use of surrogate branches in future studies. A second experiment examined the effect of dormant spray oil on pesticide transfer from treated surfaces to non-target vegetation. Experimental latticework structures were coated with an aqueous solution containing diazinon either with or without oil. Parsley plants were placed within the structures and samples were collected at 8 intervals over a 36-day period, Diazinon concentrations in parsley increased from day 3 to 21, then declined, Dormant spray oil had no effect on pesticide concentrations found in these samples over time. Results suggest that oil may not be useful in reducing pesticide transfer to non-target vegetation if those pesticides volatilize at rates or have octano1:water partition coefficients similar to those of diazinon.