BACKGROUND: Insecticide application is essential to control navel orangeworm (Amyelois transitella) in California almond and pistachios. Coverage is difficult because of tree height and applicator practices. Studies were conducted to characterize insecticide deposition by both ground and air, and to develop alternatives to the use of water-sensitive cards to assess spray coverage. RESULTS:We used almond challenge bioassays to demonstrate that insecticide application failed first in the upper canopy (5.2-6.1 m) when application speed exceeded 2.9 kph. In pistachios, we used filter paper and insecticide extraction from hulls to demonstrate that deposition increased with application volume. Typically, in ground applications, coverage decreased with height, whereas for application by air, coverage was greatest at the top of the canopy (6 m) and decreased as the spray penetrated the canopy. In the best ground applications there was no loss over height. We were able to demonstrate a dose-response relationship for methoxyfenozide using contact toxicity bioassays. CONCLUSION: Coverage was best at or below the recommended speed of 3.2 kph and improved when water volume increased.There was a 50% loss in insecticide efficacy at the height of 4-4.8 m; we suggest that future monitoring concentrate on this portion of the canopy. The best ground application provided uniform deposition throughout the canopy, whereas the applications by air were most effective in the upper canopy. The use of filter paper can provide information for chemical deposition and enable contact toxicity bioassays, whereas water-sensitive paper cannot do this. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

BACKGROUND: Insecticide application is essential to control navel orangeworm (Amyelois transitella) in California almonds (Prunus dulcis), but coverage is challenging. Laboratory and field trials were conducted from 2014 to 2017 to quantify insecticide deposition and duration of control. RESULTS:In the laboratory for filter paper, photolysis reduced the contact toxicity of bifenthrin, and its half-life was 6.2 days. For chlorantraniliprole applied in the field, there was 87-94% less insecticide deposited in the almond suture, the most vulnerable part of the nut, than on the hull. For chlorantraniliprole, adjuvant choice (alcohol ethoxylate versus mineral oil) affected both initial insecticide deposition and half-life. Chlorantraniliprole degradation was greater at 6.1 m than at 3 m for both adjuvants assessed, whereas contact mortality was similar at both heights for the alcohol ethoxylate adjuvant. CONCLUSION: The combination of photolysis and differential distribution of insecticide on the nut can account for the variable control observed in the field. This was particularly problematic in the upper canopy and adjuvant choice affected deposition and insecticide degradation. Less than 1% of the insecticide in the tank was deposited on the almond suture. These results demonstrating the fraction of the insecticide in the sprayer tank deposited on the nut target, combined with reduced coverage in the upper canopy are also applicable to the control of A. transitella in pistachio (Pistacia vera) and walnut (Juglans regia) orchards.