Emerald Ash Borer – It is Here and Active in Denton County


The Emerald Ash Borer (EAB) has been discovered in Denton, County. The ISA Certified Arborists want to make sure that our customers and the community at large have accurate information and with proper knowledge can decide how they want to protect any Ash trees on their property.

The EAB was discovered in the USA in 2002 near Detroit, Michigan. This insect is native to China, Korea, and Japan where it co-exists with a good set of predators and resistant Ash trees and not causing much damage. However, when the insect arrived in North America it found a forest of Ash trees (Fraxinus) that had not seen this pest before and with no native predators or parasites. The insect has spread across the northern United States, killing almost every unprotected Ash tree in its path. It was discovered in Texas in April 2016 when four adults were in far northeast Texas in Harrison County. In the fall of 2018, the insect was found to be in Tarrant County (north of Fort Worth).

This past week, the Tree Shepherds ISA Certified Arborists had the opportunity to assess a group of Ash trees in the City of Denton, near Corinth. EAB was found in the trees and adults had emerged and were active on the trees. Even though the USDA has not officially determined that the insect is the EAB, we want to be out in front for our customers with good information on this very destructive insect.

The EAB spreads about 15 miles per year. There are probably infestation pockets in Denton County that we do not know of yet. The known pocket that we assessed this past week is in southern Denton on the border with Corinth.

Ash trees are not the predominant tree in Denton County. Denton county is dominated by Post Oaks, Cedar Elms, Blackjack Oaks. However, the Ash can be common along the creeks and rivers and as a result is found in residential yards if they were preserved during construction. The Green Ash (Fraxinus pennsylvanica) is native to Denton County and it produces a lot of seeds that can sprout in yards and old cleared areas. Iin the 1980’s and 90’s, Arizona Ash (Fraxinus velutina) was planted widely in the yards in new developments. In recent years the Texas Ash (Fraxinus texensus), which is native south of Dallas, has begun to be planted as a shade tree in Denton County. Rarely, White Ash (Fraxinus american) may be found to be planted. All Ash trees are susceptible to the EAB.

The EAB takes 2-3 years to kill an Ash tree. The initial symptoms are a general die-back of the upper crown with the die-back continuing down the tree until it finally succumbs and dies. It is hard to detect early infestations and if there is a general decline in an Ash tree, then an ISA Certified Arborist may need to climb into the tree to determine if EAB is present.

What to Look For

Ash trees that are infested with the EAB will exhibit these characteristics:

A general die-back of the upper crown. The leaves may be a little more yellow than normal. This is a White Ash (possibly a Texas Ash) in a neighborhood in south Denton. Notice the declining upper crown. Basal suckering may also be evident as the tree tries to survive by putting out sprouts below where the insects are active. The two trees below were observed in the south part of Denton. The exhibit various stages of infestation.

The adult creates a D-shaped exit hole that is approximately 1/8 inch wide. Other borers can also make similar exit holes, so this is not definitive, but it is a strong indication if found on an Ash tree.

The infestation begins in the upper crown. The exit holes will appear their first and may not be evident in the lower crown or main trunk until year two or three of the infestation.

D-shaped exit holes of the Emerald Ash Borer.

Under the bark will be serpentine galleries where the larva of the EAB ate out the inner bark and the very outer layer of wood. The galleries are vertical, not horizontal on the limb or trunk.

Serpentine galleries of the Emerald Ash Borer.

This tree is in the final stages of an infestation. The insect has probably been in this tree for at least two years, possibly longer.


Control of the EAB is possible. If a tree has less than 25%-30% decline, then it may be possible to save the tree. Preventive control is best. Please follow this link for the best information on control of the EAB: Insecticide Options for Protecting Ash Trees from Emerald Ash Borer.

This publication has the latest information on protecting your Ash trees and the effectiveness of the various treatment options. One of Tree Shepherds ISA Certified Arborists can help you understand the treatments and decide what treat is best for you.

Decisions on Management

Each property owner will have to make decisions on what Ash trees are important to the property. Control is an ongoing process. With injection of Emamectin Benzoate, control is almost 100% for two years. This is the best treatment option but is also the most expensive. Active infestations are killed, and new infestations are prevented for those two years. However, re-treatment will be needed every 2-3 years. For trees that are central to a landscape or that provide significant shade, this on-going treatment is probably warranted. On smaller trees or trees that are not significant to the landscape or shade cover, a property owner may decide to not treat and let nature take its course. It will be up to each property owner and their unique situation as to what decision to make.

Tree Shepherds ISA Certified Arborists will provide an honest assessment for each property owner that contacts us. We provide the treatment services but will first provide a thorough evaluation of the property owner’s trees and situation. If it is decided that treatments are warranted, our arborists can price the correct treatment and perform the service. For more information about our EAB treatment options, please visit our services page.

Scott Geer

Scott Geer

Scott Geer has a master's degree in forestry from Stephen F. Austin State University and is an ISA Board Certified Master Arborist.® He is also a graduate of the American Society of Consulting Arborists Academy.