Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/1996
Publication Date: N/A
Citation: N/A Interpretive Summary: Drift of pesticides out of the sprayed area is a major concern of the public and spray applicators. Drift retardants are added to water and pesticide in a spray tank mixture to increase the average droplet size of the spray and thus to reduce drift. Many commercially available drift retardants contain long-chain molecules (polymers) which become less effective after circulating through sprayer pumps for several minutes. In this study we developed a laboratory test stand and procedure to determine the change in the drop size spectrum produced by spray mixtures containing drift retardants sheared by circulating through a centrifugal pump. Drop size spectra were measured while spraying sheared spray mixtures through a standard hydraulic, flat-fan nozzle. The laboratory procedure was compared with a commercial airblast orchard sprayer. Experiments with 3 commercial drift retardants showed that changes in droplet size for tank mixtures which were circulated through the laboratory test stand were similar to changes for the same mixtures circulated through an airblast sprayer. It is important that pesticide applicators know that drift retardants can become less effective if they are recirculated through a sprayer pumping system for extended time periods. If the retardant is not producing the expected increase in droplet size, the amount of drift from spraying an area may be greater than predicted, increasing the potential for damage to adjacent areas. Results of this study demonstrate that a laboratory test can successfully simulate the shear effects of a commercial sprayer on drift retardants. Several chemical companies suggest that this system be submitted as an ASAE Standard.
Technical Abstract: A laboratory system was developed to simulate shear on spray mixtures of water and drift retardants due to recirculation of the mixtures in sprayer tanks. Three drift retardants (AgRHO DR-2000, Nalco-Trol and Nalco-Trol II) were evaluated in both a Myers A36 orchard, airblast sprayer and the laboratory system. Droplet size distributions of sprayed samples from the sprayer and the laboratory system were measured with an Aerometric Phase/Doppler Particle Analyzer. Droplet size distributions of sprayed samples with drift retardants sheared with the laboratory system had similar trends to those of samples sheared with the airblast sprayer as the number of recirculations increased. When the number of recirculations through the laboratory system increased from 0 to 11.4, volume median diameter of sprayed samples of the 0.1% DR-2000 mixture did not change significantly from the initial value of 587 um, but volume median diameter of sprayed samples with 0.0547% Nalco-Trol and the 0.0547% Nalco-Trol II mixtures decreased from 592 to 422 um and from 505 to 366 um, respectively. Also, the percent spray volume less than 200 um for mixtures with DR- 2000 and Nalco-Trol taken after 11.4 recirculations was 72.8 and 34.1 % respectively, less than that of a water spray. For comparison, volume median diameter and spray volume less than 200 um of a water only spray was 344 um and 17.3 %, respectively.