Evaluation of Systemic Insecticides to Control Emerald Ash Borer
The emerald ash borer (EAB) is a periodic pest of ash trees in northeast Asia. In 2002, it was identified as the causal agent of ash tree mortality in southern Michigan and Ontario. EAB is now considered established throughout Lower Michigan and infestations are present in Upper Michigan, Ohio, Indiana, Illinois, Maryland, Pennsylvania, and West Virginia. It is estimated that EAB has killed over 20 million ash trees and threatens ash throughout North America. When EAB was discovered in North America, little was known about its biology and there was no information on how to detect or control it. Objective guidelines for EAB control are urgently needed to help property owners, tree care professionals and regulatory personnel determine how to effectively manage ash trees within and beyond the currently infested area. A highly effective insecticide control strategy could also become an important part of the EAB management program. Injection of systemic insecticides is often a preferred method for controlling insect pests in landscapes because it eliminates potential spray drift thereby reducing applicator exposure and it minimizes impacts on non-target organisms.
We have conducted several studies evaluating the use of systemic insecticides to control EAB from 2003-2007.
In 2003, we treated nearly uninfested green or white ash street trees in two Ann Arbor, Michigan neighborhoods. Trees were trunk-injected each year from 2003-2006. Trees were treated with either Imicide using Mauget capsules, Pointer using a wedgle, or Bidrin (dicrotophos) applied as an early or late treatment with Mauget capsules. Treatments were compared to untreated controls. All treatments were tested in one neighborhood; only Imicide/Mauget and Pointer/Wedgle were tested in the second neighborhood.
In 2006, we evaluated a non-invasive, efficient and simple method of applying imidacloprid or dinotefuron to the trunk of ash trees. This application method involves mixing the insecticide with Pentra Bark®, a non-toxic, bark-penetrating surfactant (Agrichem, Medina, OH). The formulated solution was applied directly to the bark on the lower trunk of a tree with a common garden sprayer. Trees sprayed with imidacloprid or dinotefuron were compared to untreated controls.
In 2007, treatments included trunk injection with Imicide using Mauget capsules, trunk injection with emamectin benzoate using the arborjet, a non-invasive trunk spray of Macho 2F (imidacloprid) + Pentra Bark; a non-invasive spray of Macho 2 without Pentra Bark; a non-invasive trunk spray of Safari (dinotefuron) + Pentra Bark; a non-invasive trunk spray of Safari without Pentra Bark, and untreated controls.
Each year, experiments were evaluated by collecting foliage to measure insecticide residue levels, conducting leaf feeding bioassays with adults fed foliage collected from control and treated trees, measuring larval density by removing sections of bark, and assessing canopy dieback.
Evaluation of insecticide treatments will lead to recommendations that will enable arborists and landscapers to apply highly effective treatments. Results will also assist property owners, city arborists and landscapers in predicting treatment success and determining when treatment is not appropriate.
For the 2003 experiment, results spanning four years illustrate how rapidly the density of EAB can build. The trunk injection treatments did reduce EAB density relative to untreated controls in green ash tress in both neighborhoods. In terms of long-term tree survival and condition, however, our results are somewhat disappointing. None of the trees injected with the Pointer/Wedgle in either neighborhood survived to 2006. The green ash trees injected with Imicide/Mauget in the first neighborhood exhibited relatively low dieback and 80% of these trees survived to 2006. Average dieback for the other trees injected with Imicide/Mauget, early application of Bidrin/Mauget or late application of Bidrin/Mauget ranged from 45 to 50% in 2006 and 33 to 50% of those trees survived to 2006. For green ash trees in the second neighborhood, EAB density in trees injected with either Pointer/Wedgle or Imicide/Mauget was significantly lower than in untreated control trees in 2004 and 2005. By 2006, all of the untreated control trees, and all but one of the trees injected with Pointer had been removed by the city due to advanced canopy decline. In 2006, larval density in the four remaining trees treated with Imicide/Mauget had stabilized at a level that was <20% of the maximum density in untreated control trees. For white ash trees, larval density was generally lower in the Imicide/Mauget trees than in controls or Pointer/wedgle trees in 2006. However, treatments did not significantly differ in any year.
Data from 2006 showed that the trunk sprays of imidacloprid + Pentra Bark and dinotefuron + Pentra Bark effectively moved the insecticides into the vascular tissue of trees and that the insecticides were translocated to the canopy. Dinotefuron, which is highly soluble in water, appeared to translocate relatively rapidly into the canopy. Residue levels peaked in mid June, then declined by roughly 40-50% over the next three weeks, suggesting that the product may break down relatively quickly. Residue levels in imidacloprid trees continued to increase from mid-June to July to August, suggesting that the product moved relatively slowly into the canopy or foliage. In contrast, foliar imidacloprid residues peaked in mid-June in trees treated with the trunk injection (Mauget capsules). In bioassays, beetle mortality after four days of exposure ranged from 34-61% among imidacloprid-treated trees and 62-82% on dinotefuron trees. Larval density varied considerably among treatments and sites, but was generally lower on treated than untreated trees. Differences among treatments were statistically significant at one site where larval density was roughly 50 to 75% lower on treated trees than on control trees.
In 2007, results for adult leaf-feeding bioassays conducted in June indicated that no EAB survived on leaves from emamectin benzoate trees. Beetle survival on trees treated with Safari (dinotefuron) declined to <15% by Day 4. Beetle survival on leaves from trees treated with the Mauget capsules and the Macho 2F (no Pentra Bark) was also significantly lower than survival on control trees. For adult leaf feeding bioassays conducted in early July and late July, we again observed 100% mortality of EAB on the emamectin benzoate leaves. Beetle survival was generally lower on other treated trees than on controls in July bioassays, but at least 40% of the beetles survived on leaves from the imidacloprid- and dinotefuron-treated trees. Larval density was assessed in late September by felling and debarking areas on the trunk and canopy of a subsample of the trees. Larval density varied considerably within and among treatments, as expected. Overall, imidacloprid applied either as a trunk injection (Mauget capsules) or as a trunk spray and dinotefuron provided some control. However, emamectin benzoate provided > 99% control of EAB. Results from the larval sampling and the adult bioassays indicate that emamectin benzoate probably acts primarily on adult EAB and/or neonate larvae; otherwise we would have expected to find hundreds of dead late stage larvae on the trees. Moreover, because emamectin benzoate affected adults and/or neonate larvae, the trees sustained little injury.
- Deborah McCullough, Michigan State University
- Therese Poland, USDA Forest Service - Northern Research Station Research Entomologist
- David Cappaert, Michigan State University
- Andrea Anulewicz, Michigan State University
- Phil Lewis, APHIS
- John Molongoski, APHIS
Last Modified: 04/03/2015