Emerald Ash Borer: Identifying Signs and Symptoms of Infestation

D-shaped Exit Holes

The emerald ash borer (EAB) is a highly destructive invasive species that primarily targets ash trees. One of the most distinctive and easily recognizable signs of an EAB infestation is the presence of D-shaped exit holes on the bark of the tree. These small, perfectly shaped holes are created when adult beetles emerge from beneath the bark after completing their larval stage. The shape and size of these exit holes make them a critical indicator for identifying whether a tree has been infested by this pest.

When inspecting an ash tree for potential EAB activity, it's essential to look closely at the bark. The D-shaped exit holes are typically about 1/8 inch in diameter and are positioned horizontally or vertically on the surface of the bark. Unlike other types of wood-boring insects, which may leave round or oval exit holes, the distinct "D" shape is unique to the emerald ash borer. This characteristic makes it easier for arborists and homeowners to differentiate between EAB damage and damage caused by other pests. However, these holes can sometimes be obscured by lichen, moss, or thick layers of bark, so careful observation is necessary.

To identify D-shaped exit holes, you should examine the trunk and larger branches of the tree. It's important to note that these holes will not appear immediately after an infestation begins; they only become visible once the adult beetles have emerged. This emergence usually occurs during the late spring or early summer months. If you notice these holes, it's a clear sign that the tree has already been infested, and immediate action is required to prevent further spread. Early detection through the identification of these exit holes can significantly improve the chances of saving nearby ash trees from becoming infected.

How to Inspect for D-shaped Exit Holes

Inspecting your ash trees for D-shaped exit holes requires a systematic approach. Here’s a checklist to guide you:

• Step 1: Examine the Bark Surface: Start by carefully examining the bark of the tree, paying close attention to the trunk and larger branches. Look for any irregularities or patterns that might indicate insect activity.

• Step 2: Identify the Shape: Use a magnifying glass if necessary to confirm the exact shape of the hole. Remember, the key feature is the "D" shape, with one side straight and the other curved.

• Step 3: Check for Multiple Holes: While a single hole could be coincidental, multiple D-shaped exit holes scattered across the bark strongly suggest an EAB infestation.

• Step 4: Document Your Findings: Take photographs of the holes and note their locations on the tree. This information can be valuable when consulting with a professional arborist or reporting the infestation to local authorities.

By following these steps, you can ensure a thorough inspection and take appropriate action if an infestation is confirmed.

Canopy Dieback

Another prominent sign of an emerald ash borer infestation is canopy dieback, which refers to the gradual thinning and death of leaves in the uppermost portions of the tree canopy. This symptom occurs because the larvae of the beetle feed on the inner bark, disrupting the flow of water and nutrients throughout the tree. As a result, the upper branches begin to lose vitality, leading to sparse foliage and eventual branch death.

Canopy dieback typically starts at the top of the tree and progresses downward over time. Initially, you might notice that the uppermost branches have fewer leaves than usual or that the leaves appear smaller and less vibrant. Over the course of several years, this dieback can spread to lower sections of the canopy, leaving large portions of the tree barren. In severe cases, the entire canopy may become bare, signaling the tree's decline.

It's important to understand that canopy dieback doesn't happen overnight. The process can take anywhere from two to four years, depending on the severity of the infestation and the overall health of the tree. During this time, the tree attempts to compensate for the damage by producing new growth in unaffected areas. However, without intervention, the damage will continue to worsen until the tree eventually succumbs to the infestation.

Monitoring Canopy Health

To effectively monitor the health of your ash tree's canopy, follow this detailed checklist:

• Step 1: Observe Leaf Density: Regularly check the density of the leaves in the upper canopy. A healthy tree should have lush, green foliage covering its branches. Sparse or patchy areas could indicate stress.

• Step 2: Track Changes Over Time: Keep a record of the canopy's appearance from year to year. Note any changes in leaf size, color, or distribution. Comparing observations over time can help identify trends.

• Step 3: Look for Bare Branches: Pay special attention to branches that no longer bear leaves. These could be early signs of dieback caused by EAB larvae feeding inside the tree.

• Step 4: Consult an Arborist: If you suspect canopy dieback, seek advice from a certified arborist. They can provide a professional assessment and recommend treatment options to mitigate the damage.

By staying vigilant and proactive, you can catch canopy dieback early and take steps to protect your ash trees.

Woodpecker Activity

Increased woodpecker activity is another telling sign of an emerald ash borer infestation. Woodpeckers are natural predators of the EAB larvae, which reside beneath the bark of infested trees. As these birds peck at the bark to access the larvae, they leave behind noticeable marks known as "flecking." Flecking appears as patches of stripped bark where the outer layer has been removed, exposing the lighter-colored inner bark underneath.

If you observe significant woodpecker activity around your ash trees, it could indicate the presence of EAB larvae. Woodpeckers are highly efficient hunters and often target areas with high concentrations of prey. Their behavior can serve as an early warning system, alerting you to potential infestations before more obvious symptoms like D-shaped exit holes or canopy dieback become apparent.

While woodpecker activity alone isn't definitive proof of an EAB infestation, it should raise concerns, especially if combined with other signs such as flecking or visible exit holes. Understanding the role of woodpeckers in the ecosystem can also highlight the interconnectedness of nature and the importance of maintaining biodiversity even in urban environments.

Identifying Woodpecker Damage

Here’s how you can identify woodpecker activity and determine whether it might be linked to an EAB infestation:

• Step 1: Look for Flecking: Inspect the bark for areas where the outer layer has been peeled away, revealing the lighter inner bark. Flecking is often concentrated in areas where larvae are present.

• Step 2: Listen for Pecking Sounds: Woodpeckers produce distinct tapping sounds as they search for food. If you hear frequent pecking near your ash trees, investigate further to see if there are visible signs of damage.

• Step 3: Examine the Tree Carefully: Combine visual inspections with auditory cues. Look for patterns of flecking and compare them with other symptoms of EAB infestation.

• Step 4: Seek Professional Guidance: If you suspect that woodpeckers are targeting your ash trees due to EAB larvae, consult with a local expert who can confirm the diagnosis and suggest management strategies.

By incorporating these steps into your routine inspections, you can better understand the relationship between woodpeckers and EAB infestations.

Serpentine Galleries

Underneath the bark of an infested ash tree lies one of the most unmistakable signs of an emerald ash borer infestation: serpentine galleries. These winding tunnels are created by the larvae as they feed on the inner bark, carving out paths that resemble intricate mazes. The galleries disrupt the tree's vascular system, preventing it from transporting essential nutrients and water.

To uncover serpentine galleries, you'll need to remove a section of the bark. This should only be done under professional guidance, as improper removal can cause additional harm to the tree. Once exposed, the galleries will appear as S-shaped or zigzagging tracks etched into the cambium layer. These tracks are packed with frass, a mixture of excrement and chewed wood fibers, left behind by the feeding larvae.

The presence of serpentine galleries confirms that the tree has been infested by EAB larvae. While this discovery may be disheartening, it also provides valuable information for developing a management plan. By understanding the extent of the damage, you can make informed decisions about whether to treat the tree, remove it, or implement preventive measures for surrounding ash trees.

Uncovering Serpentine Galleries

Follow this checklist to safely and effectively identify serpentine galleries:

• Step 1: Choose a Suitable Location: Select a portion of the trunk or branch where bark removal won’t severely impact the tree's health. Avoid removing bark from the base or main stem unless absolutely necessary.

• Step 2: Remove the Bark Carefully: Use a sharp knife or chisel to gently peel back the bark. Work slowly and methodically to avoid damaging the underlying layers unnecessarily.

• Step 3: Inspect for Galleries: Once the bark is removed, look for the characteristic S-shaped or zigzagging tunnels. These galleries may be filled with frass, making them easier to spot.

• Step 4: Document Your Findings: Take photos of the galleries and note their location and severity. Share this information with a certified arborist for further evaluation.

Proper identification of serpentine galleries is crucial for determining the best course of action to manage the infestation.

Wilted or Discolored Leaves

As the emerald ash borer larvae continue to feed on the inner bark, the disruption to the tree's vascular system leads to noticeable changes in the leaves. One of the earliest signs of distress is wilted or discolored leaves, which may appear yellow, brown, or prematurely fall off the tree. This symptom is often accompanied by reduced leaf size and poor overall vigor.

Wilted or discolored leaves occur because the tree cannot efficiently transport water and nutrients to its extremities. The upper canopy, being furthest from the roots, is usually affected first. Over time, the condition spreads downward, affecting more and more branches. Homeowners and property managers should remain vigilant for these subtle yet significant changes, as they can serve as early indicators of an EAB infestation.

It's worth noting that wilted or discolored leaves can also result from other stressors, such as drought, disease, or nutrient deficiencies. Therefore, it's essential to consider the broader context when evaluating the health of your ash trees. Combining observations of leaf condition with other symptoms like D-shaped exit holes or canopy dieback can help paint a clearer picture of what's happening to the tree.

Assessing Leaf Condition

Here’s a practical checklist for assessing wilted or discolored leaves:

• Step 1: Compare Leaf Color: Compare the color of the leaves on your ash tree to those of healthy specimens. Yellowing or browning leaves could signal trouble.

• Step 2: Check Leaf Size: Measure the size of the leaves and compare them to previous years' growth. Smaller leaves may indicate stress caused by EAB larvae.

• Step 3: Inspect for Premature Drop: Note whether leaves are falling earlier than expected. Early leaf drop is a common response to nutrient or water shortages.

• Step 4: Rule Out Other Causes: Consider environmental factors like weather conditions, soil quality, and pest pressures. If no other explanations seem likely, EAB infestation should be investigated further.

By following these steps, you can accurately assess the condition of your ash tree's leaves and determine whether further investigation is warranted.

Sprouting from Tree Base

In response to the damage caused by emerald ash borer larvae, ash trees often attempt to compensate by producing new growth from the base of the trunk or below the infested areas. This phenomenon, known as sprouting from the tree base, results in clusters of shoots or suckers emerging near the ground level. While this regenerative effort might seem promising, it is actually a sign of severe stress and indicates that the tree is struggling to survive.

These sprouts are typically slender and grow rapidly, often reaching several feet in height within a single growing season. They may appear lush and green, but they do not replace the lost canopy and cannot sustain the tree in the long term. Instead, they divert energy away from the main trunk and branches, further weakening the tree's structure.

Recognizing sprouting from the tree base as a symptom of EAB infestation is vital for timely intervention. By addressing the root cause of the problem, you can prevent the spread of the pest and preserve nearby ash trees from similar fates.

Managing Sprouts Effectively

To manage sprouting from the tree base, follow this detailed checklist:

• Step 1: Prune Sprouts Regularly: Use pruning shears to remove sprouts as soon as they appear. Cutting them back encourages the tree to focus its resources on healing rather than producing unnecessary growth.

• Step 2: Apply Herbicides Selectively: If sprouts persist despite regular pruning, consider applying herbicides specifically designed for controlling unwanted vegetation. Be cautious to avoid harming the tree itself.

• Step 3: Monitor Overall Tree Health: Keep track of the tree's overall condition while managing sprouts. Addressing the underlying EAB infestation is the most effective way to stop sprouting altogether.

• Step 4: Consult Professionals: For persistent or widespread sprouting, consult with a certified arborist. They can offer tailored solutions based on the specific needs of your ash tree.

Taking these steps ensures that you address both the immediate issue of sprouting and the broader challenge of managing an EAB infestation.