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April 18, 2014

Dealing With Emerald Ash Borer (EAB)

By José Fernández in | 0 Comments

There are several approved methods for protecting Ash trees from EAB, each method having varying degrees of success, and each having its own pros and cons. Out of the many treatment options available, RTE uses two main methods proven to be effective through research and personal experience. Each approach will be described briefly followed by a summary including pros and cons.

Imidacloprid Soil Drench:
This treatment was one of the first options available to arborists back in the early days of EAB prevention, when the wave of infestation was still in northern Ohio. Later research showed the chemical to be very effective when applied at double the normal rate, after which the label was adjusted so that commercial applicators could legally apply this new rate for the specific treatment of EAB in Ash trees.

This treatment is systemic, meaning that the chemical is taken up by the tree, in this case through the roots, so that when larvae feed on the phloem of the tree they ingest the chemical and die. To make the application, the arborist measures the diameter of the tree at breast height (DBH) in inches, and uses that measurement to determine the proper amount of chemical solution to apply. She may then apply the solution in a small trench around the base of the tree so that it soaks into the soil, or she may use a lance or probe attached to a hydraulic pump that will inject the solution directly into the soil. Either result is the same: the solution becomes available to the roots for uptake.

For the best uptake, soil should be moist at time of treatment, and should remain moist for some time after treatment. Trees transpire when soil is moist, which is to say they actively move water and nutrients from the roots to the canopy. The process is complex and influenced by other factors such as temperature, season and time of day, but for our purposes this simple explanation suffices.

Imidacloprid should ideally be applied at least 30 days prior to when the chemical will actually need to be present, especially in larger trees. EAB adults usually begin to fly in early June and lay their eggs soon after, so ideally imidacloprid soil drenches for this pest should be completed no later than early May. A fall application is effective but research shows a spring application may be more effective.
Note that this treatment is best when used before a tree has been infested with larvae, and should be applied on a yearly basis.

Advantages
Non-invasive to tree
Effective for healthy, uninfested trees
Several homeowner formulas available
Relatively inexpensive

Disadvantages
Best when applied at least 30 days prior
Yearly application necessary
Not the best option for infested trees

Emamectin Benzoate Trunk Injection:
At the time of this writing, emamectin benzoate is proprietary to Arbor-Jet as a treatment for EAB and is marketed under the trade name Tree-age. This treatment is also systemic, but is delivered to the tree in a direct trunk injection that requires the drilling of holes spaced around the base of the trunk. Special plugs are inserted into the holes that serve as ports through which the chemical is injected directly into the tree’s vascular system using a special trunk injection device. Uptake is much better when the tree is actively transpiring, and is much faster than the soil drench application. In addition, this chemical has the best documented results when used for treating trees that are already infested. The level of infestation must be assessed to gauge how well a tree may respond to a treatment in order to decide how effective a treatment may be. A compromised vascular system (such as that caused by heavy larval feeding) will limit the delivery of the chemical, but whatever live tissues the chemical reaches will cause larval death when feeding begins. Perhaps the curative effect of this chemical is linked to the faster delivery and uptake inherent to the trunk injection system.

This treatment is invasive, although a healthy tree can quickly compartmentalize the drill wounds. While currently more expensive than the soil drench method, Tree-age only needs to be reapplied every other year (treatment lasts two years). The chemical is only available to state licensed applicators and the equipment needed for the application can be a costly investment.

Advantages
Quick, direct delivery
“Curative” – can be effective for infested trees
Treatment lasts two years

Disadvantages
Invasive to tree
Currently more expensive
Must be applied by a state licensed applicator

Which method is best for me?
This depends on the client. In our area pest pressure is currently very high, so Tree-age is the best recommendation for trees that have not been treated before. If you have been treating your tree preventively with imidacloprid as a soil drench and your tree is currently not infested, continue to do what you are doing. If your tree is now infested, you may consider switching to Tree-age for a treatment cycle or two.

Tree-age may be the best option to protect trees while pest pressure is high. If infested trees respond to treatment, you may switch to the soil drench in a few years, moving into preventive mode. In either case, a consultation with a Certified Arborist will help decide the best course of action for you.


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