The Emerald Ash Borer (EAB) has killed millions of ash trees since its discovery in southeastern Michigan in 2002. Native to Asia, this insect was probably introduced to the United States in wood packing material carried in on cargo ships or airplanes. EAB has spread and will continue to spread into all US states where native ash trees are grown, it is not if, rather when EAB will be in every US state.
Treatment Strategy
The best protection from EAB is prevention. High value trees at risk for infestation by EAB should be treated preventively. EAB will attack all ash trees regardless of size and condition of the tree.
Mectinite tree injection treatments can be made when ever ash trees are actively growing and will provide 2 full seasons of control. Mectinite is effective against EAB on all sizes of trees and is the best option on trees greater than 25 inches. Mectinite is also the best option for trees growing in areas with heavy EAB populations. If trees are suspected of being infested, Mectinite will provide higher levels of control then other systemic options. On infested trees, assess the canopy for and target trees with no more than 30% dieback. Always work to treat trees prior to showing any symptoms as this results in the highest likelihood for success.
Transtect soil applications or systemic basal bark sprays can be applied throughout spring and into early to mid summer. Transtect has the advantage that it moves into the tree within a 2-3 weeks, this gives the practitioner an opportunity to assess the canopy after full leaf out for any signs or symptoms of EAB. Transtect will provide one season of control.
Xytect soil applications are applied in early spring as soon as soils thaw out and no later than the first week of May. Xytect can also be applied in late summer or fall to provide protection the following season. Xytect will provide one season of control.
Xytect and Transtect are most effective when applied to healthy appearing ash trees that have not been attacked or that are growing in areas with low EAB pressure. Xytect and Transtect will be most effective as preventive treatments on trees less than 25 inches DBH.
Other Treatment Practices
EAB attacks both healthy as well as stressed ash trees. First and foremost if you have a high value ash tree that you want preserved, protect against EAB with Mectinite, Xytect or Transtect. For trees that are actively being preserved consider additional cultural practices to improve tree health and vigor and prevent attack from native borers.
- Apply mulch around the base of treated trees to depth of 2-4 inches.
- In addition to proper irrigation and mulching, promote health and vigor with proper pruning and prescription based fertilization practices.
- Treatment of Cambistat every 3 years to improve fine root growth, improve drought tolerance and improve a ash trees resilience to harsh urban conditions.
Tree Injection Using Mectinite
Soil Injection/Drench or Systematic Bark Spray Using Transtect
Soil Injection/Drench Using Xytect 2F
Soil Injection/Drench Using Xytect 75WSP
Expected Results
- Preventive treatments will provide greater likelihood for success than treatments on infested trees.
- Recognize that it is difficult to detect the presence of EAB during the early stages of infestation thus ash trees may be protected from EAB by applying treatments prior to the onset of visible symptoms.
- In Michigan, ash trees that are not protected in certain areas have been killed over a 4-8 year period. EAB pressure may decrease once unprotected ash trees are no longer present.
- When symptoms are present, the tree has been infested for up to several years and the chance of saving it decreases. Trees with up to 50% symptoms have been saved. However, treating infested trees carries higher risk of failure.
- Continuous treatments are required for continued protection. If applications cease, trees will become susceptible to the pest.
- Xytect 75 WSP and Xytect 2F may take 30-60 days or more to be taken up into the tree toprotect the tree from EAB attack.
- Transtect soil and systemic basal bark sprays will provide faster protection (30 days of less) than Xytect soil applications.
- For Transtect bark sprays, research at Ohio State has demonstrated that 8 packets per gallon is effective on trees up to 25 inches. Use 12 packets for larger trees and trees that are under higher EAB pressure. For optimal results begin bark spray treatments when ash trees are still healthy appearing, prior to any EAB crown symptoms.
- Mectinite is the only product that has provided two years of control with a single application.
- It is important to communicate to property owners that treatments on infested trees typically result in an improvement after the 2nd full season following treatment as the tree repairs previous damage and prevents future damage.
Signs of Damage
Adult beetles feed on leaves and it is uncertain what impact adult feeding has on tree health. Larvae, on the other hand, feed on the inner bark and disrupt the movement of water and minerals within a tree causing eventual dieback, decline, and death of the tree. Symptoms of an early infestation may be difficult to diagnose. Be on the look-out for multiple declining ash in a given area. As an infestation progresses, small vertical splits in the bark can be seen on twigs or the main trunk, epicormic shoots may be visible, and woodpecker holes may be present on trees. Trees may die after 2-4 years or less (small trees).
Typically the top 1/3 of crown dies first and works its way down the tree; trees appear to lose about 30%-50% of their canopy after 1-3 years of infestation depending on the overall pressure of EAB in a given area
- As the top of the tree continues to decline, epicormic shoots form at the interface between healthy and dead tissue, anywhere in the canopy, or at the base of the tree
- Distinct “S” shaped, frass-filled larval galleries that can range from 4- 20 inches in length score the outer sapwood and phloem underneath the bark
- Galleries from an individual larvae become progressively wider as the larvae grows
- D-shaped exit holes that are approximately 1/8 inch in diameter are generally present after an infestation has been present for 1 yr. or more
- Adults are slender and can be 1/4 inch to 1/2 inch in length, they are bronze or golden green with dark metallic emerald green wing covers
- Top of the abdomen under the wings is metallic purplish red (seen when wings are spread)
- Larva are slender, flattened, segmented (10 total abdomen segments) cream colored larvae with a brown head can be found by peeling back loose bark on infested trees
- Larvae range in size from 1 -1 1/4 inches in length
- Pincer-like appendage on the last segment
Photo: Thinning canopies are symptoms of EAB
Photo: D-shaped exit hole
Photo: Larval galleries under the bark
Trees At Risk
- All ash, even healthy trees, will be attacked if beetle populations are high enough
- Some evidence to suggest that black ash is preferred over other species
- EAB can infest ash trees as small as 1” DBH up to the largest specimen trees
- Stress increases vulnerability and tree death
- EAB has also killed seemingly vigorous trees growing under optimum conditions (especially as beetle densities build)
Biology
EAB lays its eggs on the bark of an ash tree and the larvae tunnel through the bark and begin consuming the sapwood of the tree. This feeding disrupts water flow to the canopy dehydrating and killing that portion of the tree. Eventually, the whole tree will die.
- Larvae hatch from eggs deposited in bark crevices.
- Larvae chew through the bark and begin feeding on phloem.
- Feeding is completed in autumn and pre-pupal larvae over winter in the outer sapwood or bark.
- Pupation begins in late April or May.
- Newly formed adults will often remain in pupal chamber for 1-2 weeks prior to emergence in late May into Mid-August.
- Adults begin to emerge at 400 GDD and peak at 1000 GDD.
- Some larvae may require a second year of maturation feeding prior to emerging the following year as adults.
References
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.
