Tree Disease Treatment Options for Ash Dieback in Massachusetts

Understanding the Ash Disease Complex in Massachusetts

Ash dieback is a term used to describe a variety of disease conditions affecting ash trees (Fraxinus spp.). Because there are many possible causes of ash dieback, it is critical to identify the type of disease you are dealing with in order to implement the right disease treatment for your ash tree. Presently, Massachusetts is under heavy attack by the emerald ash borer (EAB), an invasive beetle that has been found in Worcester County and in other parts of central Massachusetts. Although the fungus causing ash dieback, known as Hymenoscyphus fraxineus, has not yet been found in North America, it represents a serious future threat to ash trees that we watch very closely.

Emerald Ash Borer: The Main Current Threat

The EAB feeds on all native North American ash species, which include white ash (Fraxinus americana), green ash (Fraxinus pennsylvanica), and black ash (Fraxinus nigra) that are commonly found in Worcester-area properties. As the EAB larvae eat beneath the bark of the ash tree, they create tunnels or galleries that interfere with the flow of nutrients and water to the rest of the tree, eventually killing the tree in 2-4 years after the tree becomes infested.

Symptoms of an infestation include dying branches in the upper part of the tree (canopy dieback), increased woodpecker activity creating “blonding” patterns on the bark, and vertical bark cracks above the EAB larval galleries. Mature ash trees are the most likely to suffer a quick decline when they become infested.

Fungal Ash Dieback: A Possible Future Danger

Hymenoscyphus fraxineus, the fungus that causes ash dieback, has not been identified in Massachusetts or anywhere else in North America. It has, however, had a devastating effect on European ash populations, with mortality rates estimated at 80-85% where the fungus has taken hold. Given these effects, tree care professionals are vigilant for signs of the fungus being introduced into Massachusetts either naturally via spores or artificially through imported plant materials.

The symptoms associated with ash dieback will be different than those associated with the EAB. These include darkened patches on leaves during the summer, premature leaf fall, diamond-shaped bark lesions, and gradually declining crowns as the fungus continues to infect the tree, as opposed to the EAB killing the tree rapidly.

Present Treatment Methods for Emerald Ash Borer

In order to treat the emerald ash borer, effective tree disease treatment methods rely on systemic insecticides that travel through the tree’s vascular system to kill the EAB larva that is eating underneath the bark. Certified arborists in Massachusetts use several evidence-based treatment options depending on the size of the tree, its condition, and its surrounding environment.

Systemic Insecticide Treatments

Currently, the most effective systemic treatment for controlling emerald ash borers is emamectin benzoate. This restricted-use insecticide is injected directly into the trunk of the tree by trained professionals and can protect the tree for 2-3 years if applied at the correct time. Systemic treatments work best on trees with less than 30% canopy loss, so early intervention is key to achieving good results.

Another systemic treatment option is imidacloprid, which is available for use as a soil drench, soil injection, or trunk injection application. While slightly less effective than emamectin benzoate, imidacloprid treatments are less expensive and can protect the tree for 1-2 years if applied at the correct time.

Finally, dinotefuran is a systemic insecticide that is applied as a basal bark spray. Dinotefuran absorbs through the bark of the tree and is an effective treatment option for smaller ash trees, and can provide protection against the EAB when applied correctly during the labeled timing window.

Timing of Applications

Massachusetts applies systemic treatments for the EAB at the correct times to maximize efficacy while minimizing harm to non-target organisms. Spring applications of systemic treatments are applied 30 days before the peak emergence of adults in late May to establish the highest systemic concentration in the tree at the time eggs begin to hatch.

Summer applications of systemic treatments are applied during the months of June through August and can be effective in controlling the EAB larvae that are currently eating beneath the bark of the tree. However, applications need to be made in the early morning hours when the temperature is not too high to allow for the best uptake and to minimize the stress to the treated tree.

Based on local emergence patterns and assessments of individual tree health, Worcester Tree Trim and Removal develops a customized treatment schedule for each property owner’s ash trees to ensure optimal timing.

Assessments of Individual Trees

In order to make informed decisions regarding the cost-effective management of ash trees, property owners should obtain a professional assessment of each tree to determine the most suitable course of action.

Evaluation of Tree Health

Certified arborists evaluate multiple characteristics when assessing the suitability of ash trees for treatment. Characteristics include tree size, health, location, and level of infestation that all play a role in determining the recommended treatment approach. Ash trees that show greater than 50% canopy dieback rarely respond positively to treatment and may need to be removed for public safety purposes.

Valuable ash trees located in highly visible areas, such as those providing shade adjacent to historic homes in downtown Worcester, or mature ash trees that frame scenic views around Holy Cross’ campus, generally justify the expense of treating the EAB because of their contribution to the aesthetic appeal and property values.

Selection of Site-Specific Treatments

The choice of treatment method depends on the size of the tree, site access, and environmental factors. Larger trees typically require professional application of systemic insecticides using trunk injection methods, whereas smaller trees may be successfully treated using soil-applied systemic treatments that can be applied by homeowners under the guidance of a certified arborist.

For properties containing multiple ash trees, comprehensive treatment programs can be implemented to protect the healthiest and most valuable ash trees, while developing plans to strategically remove and replace severely affected ash trees.

Combining Chemical Treatments with Cultural Practices and Long-term Planning

Comprehensive ash tree management involves combining chemical treatments for the EAB with cultural practices and long-range planning to address both existing threats and future sustainability issues.

Integration of Biological Controls

As part of a federal biological control program, Massachusetts has participated in the introduction of three parasitic wasp species that are designed to suppress EAB populations. These wasps are Tetrastichus planipennisi, Spathius galinae, and Oobius agrili.

Although biological controls will not save an individual tree in the short term, they may help to reduce the overall population pressure over the long term, thereby increasing the amount of time that chemical treatments will last and reducing the total cost of long-term management.

Detection Programs and Preventative Measures

Early detection programs are necessary to identify new infestations before extensive damage occurs. Property owners should be aware of early symptoms of infestation and report any suspect finds to the Massachusetts State Forestry Department or a certified arborist for confirmation.

Property owners can prevent the human-assisted movement of the EAB from one area to another by not moving ash, firewood, or plant materials. Residents of Worcester County should buy locally produced firewood and refrain from transporting ash materials from infested areas.

Preparing for New Diseases

Although the primary focus is on managing the current EAB threat, tree care professionals also prepare for new introductions of ash diseases, such as the fungal ash dieback that has devastated European ash populations.

Monitoring and Reporting Systems

Massachusetts maintains active monitoring systems to detect new tree diseases, including the possibility of introducing fungal ash dieback to North America. If property owners notice symptoms on ash trees that do not resemble the typical EAB symptoms, especially symptoms appearing on leaves during the growing season, they should report them to the Massachusetts State Forestry Department or to a certified arborist.

Vigilant observation of ash trees by property owners, landscapers, and tree care professionals is required for early detection of new diseases that could impact local ash tree populations.

Planning for the Future

Successful ash tree management requires planning for both the immediate needs of the trees and the long-term sustainability of the forest landscape. Each property owner should develop a management plan that outlines treatment schedules for valued trees, removal dates for significantly damaged trees, and replacement strategies for the newly cleared area.

By incorporating multiple species of trees, each property can reduce its reliance on a single species and reduce the likelihood of suffering from widespread tree diseases. Native alternative species such as red oak (Quercus rubra), sugar maple (Acer saccharum), and American basswood (Tilia americana) can provide similar canopy cover while reducing the risk of disease.

Professional Treatment Services

To successfully manage ash trees for the EAB, property owners need to hire a certified arborist who possesses the knowledge of local disease pressures, timing of treatments, and the correct technique for applying systemic insecticides. Certified arborists also possess the necessary licenses to apply restricted-use pesticides and maintain liability insurance for their professional services.

Professional services offer a complete assessment of each tree, application of treatment products, and continued monitoring to measure the efficacy of treatment and adjust management strategies as needed.

Worcester Tree Trim and Removal uses local experts, combined with current evidence-based treatment strategies, to provide property owners in Central Massachusetts with effective tree disease treatment methods that are relevant to their unique location and property circumstances.