Issue 6, May 31, 2011

Emerald Ash Borer Control

This is an ideal time to apply systemic insecticidal controls for emerald ash borer. Movement of systemic insecticides in a tree relies on transpiration, the loss of water from the leaves primarily through the stomata, resulting in a pulling of replacement water from the soil and up the trunk, bringing systemic insecticide with it. At this time of year, ash leaves have expanded and are very active in photosynthesis, resulting in high levels of transpiration. Although movement into the tree is perhaps quickest at this time of year, application of systemic insecticides is recommended whenever active leaves are present for four to six weeks after application. Realize that in the fall, an abscission layer forms near the base of the leaf petiole before leaves turn to fall coloration, greatly reducing the flow of systemic insecticides in the tree until the following spring.

Continued research reveals that a very important mechanism of controlling emerald ash borer is killing the adult beetles when they feed on the leaves. Spraying the foliage when adult beetles are present with a contact insecticide results in a very significant reduction in larvae within those trees later in the growing season. Suggested insecticides include bifenthrin (Onyx), carbaryl (Sevin), cyfluthrin (Tempo), or permethrin (Astro). These insecticides require annual application to the entire canopy. In many landscape situations, this spraying of tall trees will not be acceptable to clientele.

It is appearing that adult beetle mortality may be the most important control mechanism with annual application of systemic insecticides such as imidacloprid (Merit, Imicide, Xytect, others) and dinotefuran (Safari). Treated trees reveal reduced larval populations but few dead larvae in their feeding tunnels. Imidacloprid is effective when applied as a bare soil drench, soil injection, or trunk injection. Dinotefuran is applied as trunk surface spray application.

Ememectin benzoate, sold as Tree-Age, is still considered to be the most effective insecticide in the control of emerald ash borer. Continued research reveals apparently high beetle mortality resulting in fewer larvae combined with a high percentage of dead larvae in their feeding tunnels. Research continues to show high levels of control with application every two years. This increased level of control over any other proven insecticide makes it the choice for active infestations involving heavy beetle attack.

Foliar sprays as well as imidacloprid and dinotefuran applications will provide acceptable control when beetle numbers are low. They are effective preventative control options as well as when the beetles are just entering the neighborhood and when most untreated trees have died in a neighborhood.

Azadirachtin, sold as TreeAzin 2, has been shown to be effective in controlling emerald ash borer when injected into trees up to two inches dbh (diameter breast high). The insecticide was found at effective levels in the leaves of injected ten inch diameter ash, but these trees were not evaluated for larval control. Azadirachtin is an insect growth regulator, being primarily effective against developing larvae. Even though it moves into the leaves of injected trees, it does not kill adult beetles feeding on the foliage. Even though TreeAzin 2 is promoted for application every two years, annual application appears most likely to provide the best control. Too little research has been conducted for it to be recommended as a control option for Illinois. However, with its source being the neem tree, it is the only organic insecticide available that has shown any meaningful control of emerald ash borer. (Phil Nixon)

Phil Nixon

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