Protective neighboring effect from ash trees treated with systemic insecticide against emerald ash borer

Authors: DE ANDRADE, RAFAEL - University Of Maryland; ABELL, KRISTOPHER - University Of Maryland; Duan, Jian; SHREWSBURY, PAULA - University Of Maryland; GRUNER, DANIEL - University Of Maryland

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2020
Publication Date: 8/10/2020
Citation: De Andrade, R.B., Abell, K., Duan, J.J., Shrewsbury, P., Gruner, D.S. 2020. Protective neighboring effect from ash trees treated with systemic insecticide against emerald ash borer. Pest Management Science. 2020 (8) (online): 1 -8. https://doi.org/10.1002/ps.6041.
DOI: https://doi.org/10.1002/ps.6041

Interpretive Summary: The emerald ash borer (EAB) is the most costly and destructive invasive pest of ash trees in North America. We evaluated the potential for protection of neighboring (untreated) ash trees against the invasive beetle by treating several large trees in a woodlot with the systemic insecticide emamectin benzoate via trunk-injections. EAB infestations in untreated trees decreased in relation to their proximity to treated trees, showing that there is a neighboring protective effect of treatment. However, for a tree to be safely left untreated it must be close to treated trees. This level of proximity is rare in forests but can be found in urban/planted landscapes.

Technical Abstract: Native to north-eastern Asia, the emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) is now the most costly and destructive invasive species in North America. While biocontrol using introduced parasitoids shows promising results, interim strategies are needed to protect high value trees against invasive EAB populations in urban, suburban and managed forest systems. Emamectin benzoate is an effective and commonly used systemic insecticide for protection of valuable urban and heritage trees against EAB. Methods that optimize the use of emamectin benzoate allow for reduced quantities of insecticide to be released in the environment and save time and money in public and private efforts to protect ash trees from EAB. We hypothesize that a tree treated with emamectin benzoate can also offer a protective neighboring effect to nearby non-treated ash trees, allowing for an optimized spatial planning of insecticide applications. We sampled 896 non-treated ash trees in the vicinity of treated trees in five urban forests in the State of Maryland and one in Washington DC. We recorded signs of EAB infestation, namely canopy condition, exit holes, wood pecks, epicormic growth, and bark splits. Two subsequent yearly samplings were made of 198 and 216 trees respectively. We also present a proximity index that is simple but novel in this particular application. Results show a consistent decrease in EAB infestation signs in non-treated trees as proximity to treated trees increases, supporting that a neighboring effect occurs. There is also evidence of decay of the effect with time. However, our results indicate that proximity to treated trees has to be high for a tree to be safely left untreated. This proximity seems rare in forests, but can happen in urban/planted landscapes. Future studies in locations with clustered trees should test and validate these findings and could lead to a more predictive model that can derive a more precise recommended safe index across multiple ash species and geographic regions.