Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: 9/2/2009
Publication Date: N/A
Citation: N/A Interpretive Summary: One of the great challenges in assessing insecticide efficacy is determining whether the application actually protected the target. In dealing with the navel orangeworm, there are several lifestages that can be targeted (egg larva and adult) depending on the insecticide. We developed novel assays employing navel orangeworm eggs that measured insecticide coverage of pistachio nut clusters. These assays consist of pinning eggs into the nut clusters, exposing them to insecticide, removing them after 24 hours and then determining survival. We combined these assays with the use of spray cards placed at fixed intervals on PVC piping, in order to assess the relationship between the the number of droplets per square inch and height. At a distance of 14 feet above ground, the number of droplets was halved, and at 20 feet above ground there was a 90% reduction. These differences increased when tractor speed was increased. This research demonstrates that spray coverage is greatest below 14 feet and that new assays are needed to determine spray coverage at greater heights. Understanding this dropoff will increase control and decrease pistachio damage.
Technical Abstract: A novel method employing eggs was designed to assess insecticide coverage in pistachio clusters. Strips of paper towel with known numbers of eggs were pinned into pistachio clusters immediately before insecticide application. The eggs were removed 24-48 hours after application and placed on diet, reared at 85°F, and the number of surviving larvae determined 14 days after exposure. This assay was paired with the use of spray cards mounted at fixed intervals on pvc pipes. There was an inverse relationship between the number of droplets per unit area and card height, indicating that coverage diminished with height. There were 50% fewer droplets at 14 feet compared to 8 feet, and by 20 feet the coverage was reduced 90%. Coverage at faster speeds was assessed and the magnitude of the dropoff increased substantially. This research indicates that covering heights greater than 14 feet is problematic and that coverage decreases with tractor speed as well. Publicizing this dropoff will help spray applicators decrease their application speed and increase the efficacy of the sprays.