Refining Trunk Injection Strategies for Control of Foliar Insect Pests and Disease in Michigan Apple Orchards

REFINING TRUNK INJECTION STRATEGIES FOR CONTROL OF FOLIAR INSECT PESTS AND DISEASE IN MICHIGAN APPLE ORCHARDS By Charles Clark Coslor In conventional apple orchards, insect pests are managed with insecticides delivered to the canopy using airblast sprayers, which provide good canopy coverage. However, spraying results in significant product loss: as little as 26% is estimated to reach the tree canopy due to spray drift and less than 0.1% of insecticide ends up reaching the target pest. The remainder is lost to the environment with potential to harm people or non-target organisms. Trunk injection is a discriminating pesticide delivery system which reduces insecticide inputs and environmental exposure by delivering chemicals directly to the vascular system. It is commonly used to deliver pesticides in ornamental and shade trees. Recent work with trunk injection in apple orchards has shown promise, but more research must be done to determine efficacy and safety in tree fruit crops. In the following studies, we injected emamectin benzoate, imidacloprid, dinotefuran, spinosad, chlorantraniliprole, and abamectin into apple trees to expand the list of insecticides compatible with trunk injection. Nectar and pollen were sampled from trees to compare the effects of injection timing on insecticide concentration in floral resources. In addition, two fundamental injection tool types were compared: drill-based and needle-based. To test compatibility of combined insect and disease management, an insecticide and a fungicide were injected simultaneously. Finally, low-volume injections were performed on nursery apple trees, which normally require high pesticide inputs and do not produce fruit for several years. Emamectin benzoate, chlorantraniliprole and abamectin resulted in moderate to high mortality and reduced feeding in Choristoneura rosaceana bioassays using leaves sampled from trunk injected apple trees. Neonicotinoids reduced Empoasca fabae density in field evaluations, and also showed activity on C. rosaceana at higher concentrations. Spinosad was not welltransported within the apple tree vascular system. Numbers of E. fabae nymphs were lower on trees injected with imidacloprid using a drill-based tool compared with untreated trees in all years, despite a trend of initially higher foliar concentrations with the needle-based tool. This demonstrated that delivery method is an important factor in effective trunk injection based apple management. We found that when an insecticide and a fungicide are injected, they can interact dynamically within the vascular system of a tree. Injections of emamectin benzoate followed by phosphorous acid into the same set of injection ports resulted in higher mortality of C. rosaceana larvae and lower incidence of apple scab compared with untreated trees. This has important implications for expanding the utility of trunk injection for fruit tree management. Nursery tree injections were most effective when emamectin benzoate was injected into the trunk versus the taproot. A rate equivalent to 1/8 the rate used for mature tree injection reduced insect pests more than a 1/80 rate. The higher rate of emamectin benzoate was also persistent in the following year. Imidacloprid and emamectin benzoate were injected in the spring and fall, and nectar and pollen were sampled the following spring. Imidacloprid was not detected in nectar or pollen when injected in the previous spring. Conversely, emamectin benzoate was detected when injected in the previous spring, but was not detected in nectar or pollen when injected in the fall. This study expanded the list of insecticides compatible with trunk injection, demonstrated novel uses of trunk injection to reduce insect pests in apple trees, and introduced possible ways to mitigate accumulation of insecticides in nectar and pollen.