Droplet size characterization of three aerial malathion spray programs

Abstract

The Mediterranean fruit fly, Ceratitis capitata, and the Mexican fruit fly, Awls.:. trnpha lu<lens are major agricultural pests, capable of destroying a wide variety of fruit. It is the policy of the California Department of Food and Agricult ure (CDFA) to pursue eradication of fruit fly populations to prevent establishment in California. A component of the eradication efforts in the past has been the aerial application of a malathion UL V/Nu-Lure® bait mixture. Three aerial spra y pro­ grams have been monitored by the Environmental Hazards Assessment Program of CDP A. Specifically, these were the eradication of the Mediterranean fruit fly (Medfly), in the Santa Clara Valley in 1981 (Oshima et. al. , 1982) and the Los An­ geles area in 1990 (Segawa et. al., 1991) and the Mexican fruit fly (Mexfly) in the El Cajon (San Diego ) area in 1990 (T urner et. al., 1991). Extensive monito ring of the 1981 application and resulting public and environmental exposure have been presente d (Discher, 1982; Finlayson et. al., 1982; Grether et. al., 1987; Oshima et. al., 1982). The two 1990 eradication programs were less extensivly monitored. One of the components of the monitoring program s for these sprays was the col­ lection of droplet size data. Because of the possibility of additional aerial applica­ tions of malathion/bait in future eradication projects, additional analysis of the droplet size data from the three previous studies was undertaken. Continuing pub­ lic concern over the aerial application of malathion/bait warranted additional anal­ ysis of droplet size because of possible effects of droplet size on drift and vol­ atilization of malat hion. Therefore, the primary focus of the analysis was on droplet size differences between spray programs and on droplet size as it affects human and environmental exposure. The differences in aerial applicat ions be­ tween 1981and1990 add some confounding effects to the analysis. However, given the large amounts of time and effort which have gone into the collection of the monitoring data in the past and the expense that would be required to conduct a controlled aeri al exposure for experimental monitoring purposes, this analysis is the only realistic option available at the present time.