About Emerald Ash Borer
Emerald ash borer is an exotic insect from Asia that attacks ash tree. Since its accidental introduction in the mid-90s in Michigan it has spread out through more than 30 states and has killed nearly 100 million ash trees. The insect cannot be eliminated from the landscape, so treatments focus on either preventing an attack on an individual tree or killing an existing infestation in a tree.
Identifying Infested Trees
Infested trees can be identified by woodpecker pecks and blonding in the upper canopy of an ash tree (Figure 1). The woodpeckers are searching for the emerald ash borer larvae that is feeding beneath the bark (Figure 2).
View How to Identify an Ash Tree Infested by Emerald Ash Borer for additional tips.
Figure 1. Blonding of the ash tree as woodpeckers search for the emerald ash borer.
Figure 2. The emerald ash borer larvae beneath the bark.
Lifecycle & Behavior
The insect emerges from an infested tree as an adult from late May until August with most emergence occurring in June (Figure 3). The adults lay eggs on the bark and once the eggs hatch the larva burrow into the tree feeding in the phloem, the tissue that carries food throughout the tree. The larvae feed from one summer till the next spring before becoming a pupa and then emerging as an adult. It usually takes repeated attacks over four or five years to kill a tree.
Figure 3. An adult emerald ash borer.
Insecticide Management Options
There are many different active ingredients, products, and application methods available for managing emerald ash borer. Some products are available for homeowners to use, but the most effective are restricted to commercial applicators.
When is treatment necessary?
Treatments are not recommended until emerald ash borers have been detected within 15 miles of your tree’s location. Once the insect has been confirmed in your area, treatments are the only means of protecting an ash tree from being killed by this insect.
Emerald ash borers only attack ash trees (Fraxinus). They will not attack mountainash (Sorbus) so there is no need to treat these flowering trees.
What treatments are available?
Treatments are not a vaccine. They must be applied either annually or biennially depending on the application and chemical used. Several products can also be used therapeutically, to kill an existing infestation in a tree, while others only protect a tree from becoming infested.
There are three methods of applying insecticides to your tree:
Require annual application, restricted to mid-spring and autumn, and are used to protect trees from becoming infested.
There are insecticides available to homeowners as soil trenches. Commercial applications may also use soil injections (Figure 4).
Insecticides delivered as a soil drench should be applied at the base of the trunk, within a foot, with the sod or mulch pulled away before making the application. The sod or mulch can be put back in place after the insecticide solution soaks into the soil. Soil injections should be made within 18 inches of the base of the trunk and injected to a depth of 2 to 4 inches. Injections made farther from the trunk and deeper into the soil are less effective.
Figure 4. Insecticides can be injected into the soil, taken up by the roots and then carried throughout the tree to kill the insect.
How Much to Use
The amount of chemical used for soil drenches and injections is based upon trunk diameter. Since trunk area increases at a different rate than trunk diameter, these treatments become less effective for tree larger than 15 inches dbh1 and are best limited to trees less than 10 inches.
There are some specific labels that allow a 2x rate for trees between 15 and 22-inch dbh. However, note there is a restriction of the amount of imidacloprid that can be applied to the soil per acre per year.
When to Apply
Soil applications of imidacloprid formulations should be made starting just after the leaves have opened until about early June. Treatment may also be applied after Labor Day until the leaves begin to drop for protection the following year.
Soil applications of dinotefuran formulations move quickly throughout the tree so can be made beginning when the tree leaves have opened until about the middle of July.
All soil treatments need to be applied annually and at the highest labelled rate to protect an ash tree from becoming infested. They are not effective in trees that are already infested by the emerald ash borer. Formulations available to homeowners have provided inconsistent management of emerald ash borer. It is best to hire a commercial applicator to provide treatments.
Soil application should only be made in moist soils, preferable soils that have been watered the day or evening before application. Soil applications can also result in contamination of ponds, lakes and streams and some have restriction for use within 100 feet of water.
Insecticides delivered via soil applications can also be absorbed by surrounding plants so should not be used if flowers, which may be attractive to pollinators, are beneath the canopy of the tree.
|Table 1. Soil Insecticides.|
Safari™ (20 SG)
Bayer Advanced™ Tree & Shrub Insect Control2
Require annual application, restricted to midspring through midsummer, and are used to protect trees from becoming infested.
Insecticides can be sprayed on the lower trunk of the tree (the lower 6 feet). These chemicals are absorbed through the bark. They are carried up by the sap flow to kill the larvae beneath the bark and adult beetles feeding on the leaves.
There is one active ingredient that can be delivered via trunk spray. The spray does not need to be made at high pressure (the water pressure coming from a garden hose is sufficient). Surfactants may be used to improve absorption through the bark but are not necessary.
When to Apply
Systemic bark sprays should be applied to protect trees from becoming infested. They are not effective in trees that are already infested by the emerald ash borer. They need to be applied annually and are best applied after the leaves have opened till about middle of July.
|Table 2. Systemic Bark Sprays.|
Require either annual or biennial application, wider time frame during the season for application, and may be used to protect trees from becoming infested or kill an existing infestation in a tree (depending on label).
Insecticides can be delivered by directly injecting into the trunk (Figure 5 and Figure 6). Trunk injections do create wounds in the tree, but if the injections are done low on the trunk, at the flare and not adjacent to a previous injection site, then the injury is minimal, and the insecticide will be distributed throughout the canopy.
The uptake and distribution of trunk injected insecticide is quicker than that delivered via the soil. The soil should be moist, not dry or wet, to improve uptake of the chemical through the tree. Watering the soil around the tree a day before injection will sufficiently irrigate the soil.
When to Apply
Trunk injections should be made between after the ash tree leaves have opened and before the end of June. Injection may be made even later into the summer, but uptake of the chemical is slower to be distributed through the tree. However, it is still better to inject a tree in midsummer then wait until the following spring. Autumn applications can be made with some products for protection the following year but these need to be completed before the leaves begin to drop.
Emamectin benzoate injections can provide two years of protection for a tree becoming infested. Emamectin benzoate products can be used on trees that are already infested. Trees that have less than 35% canopy decline due to an emerald ash borer infestation can be injected. If the tree has more dieback or decline, then there will be insufficient distribution of the chemical and the tree will continue to decline.
Other active ingredients generally provide only a year of protection and may be better suited for trees that are not already infested.
|Table 3. Trunk Insecticides.|
|Active ingredient||Product||Injection System|
ArborSystem Direct-Inject System
|ArborSystem Direct-Inject System
Rainbow Treecare Scientific
Advancement M3 injector
1Diameter of the tree at 4.5 feet above the ground.
2Available to homeowners.
SG – Soluble Granules
WP – Wettable Powder
WSP – Water-Soluble Packets
Disclaimer: Any treatment recommendations, including those identifying specific active ingredients, are for the convenience of the reader. The active ingredients mentioned in this publication are generally those that are most commonly available in pesticides used in South Dakota for Turf & Ornamentals and the inclusion of an active ingredient shall not be taken as an endorsement or the exclusion of one labeled for use a criticism regarding effectiveness. Please read and follow all label instructions and the label is the final authority for a product’s use on a particular pest or plant.