Emerald Ash Borer

What Is Emerald Ash Borer?

The Emerald Ash Borer (EAB) is a highly destructive, invasive beetle that specifically targets ash trees. Native to Asia, this metallic green insect was first discovered in the U.S. in 2002 and reached Missouri by 2008. Since then, it has devastated millions of ash trees across the Midwest, including right here in the St. Louis area.

What makes EAB so dangerous is the way it attacks from the inside. While adult beetles feed on leaves, it’s the larvae that cause the most damage. They burrow beneath the bark and tunnel through the tree’s vascular system, cutting off the flow of water and nutrients. This silent destruction continues unnoticed until the tree begins to show signs of decline, often too late to reverse the damage.

If not detected and treated early, Emerald Ash Borer infestations typically kill a tree within 3 to 5 years. With ash trees making up a large portion of the urban canopy in St. Louis, this pest poses a serious threat to both residential properties and city landscapes.

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Signs Your Tree Might Have Emerald Ash Borer

Emerald Ash Borer damage often goes unnoticed until it’s advanced, which is why early detection is so important. If you have ash trees on your property, here are the most common signs to watch for:

• Canopy Thinning and Dieback
  The top of the tree begins to lose leaves and look sparse. This is often one of the first visible signs of internal damage caused by EAB larvae.
  
  
• D-Shaped Exit Holes
  Adult beetles create small, D-shaped holes (about 1/8 inch wide) in the bark when they emerge. These are usually found high up on the trunk or branches.
  
  
• S-Shaped Larval Tunnels
  Under the bark, EAB larvae carve winding, S-shaped galleries as they feed. These tunnels disrupt the tree’s nutrient flow and can be seen if the bark peels away.
  
  
• Vertical Bark Splits
  As larvae feed beneath the bark, trees may develop vertical cracks along the trunk, exposing larval tunnels underneath.
  
  
• Epicormic Sprouts
  New shoots or branches may start growing from the trunk or base of the tree as it tries to recover from stress.

• Bark Blonding
  Increased woodpecker activity, especially during winter, can strip bark in patches as they search for larvae, leaving pale or “blonded” areas on the trunk.

How Emerald Ash Borer Spreads to Other Trees

Emerald Ash Borer doesn’t just affect a single tree, it poses a widespread threat to every ash tree in your area. Once established, this invasive pest spreads quickly, often going undetected until it’s too late.

Adult beetles can fly up to a few miles from the tree where they emerged, allowing them to naturally infest nearby ash trees. However, the most common way EAB spreads long distances is through human activity, especially the movement of infested firewood, logs, or nursery stock. That’s why transporting firewood across counties or states is strongly discouraged and often regulated.

Because ash trees are so common in St. Louis and surrounding areas, a single infestation can lead to widespread tree loss in a matter of years. If even one ash tree on your property is infected, nearby trees, on your neighbor’s property or along city streets, are at risk too.

Stopping the spread starts with early detection, responsible wood handling, and working with certified arborists to monitor and manage the health of ash trees in your landscape.

Common Trees in Missouri at Risk from Emerald Ash Borer

The Emerald Ash Borer exclusively targets ash trees, which have long been a staple in both natural forests and residential landscapes throughout Missouri and the St. Louis region. Because ash was widely planted along streets, in parks, and in yards due to its fast growth and attractive form, EAB poses a serious threat to a large portion of our urban canopy.

Here are the ash species commonly found in Missouri and St. Louis that are highly susceptible:

• Green Ash (Fraxinus pennsylvanica)
  One of the most widely planted shade trees in the Midwest. Green ash has been heavily impacted by EAB, with entire rows of street trees lost in many neighborhoods.
  
  
• White Ash (Fraxinus americana)
  Common in both natural woodlands and cultivated landscapes. Known for its strong structure and fall color, but extremely vulnerable to EAB attack.
  
  
• Blue Ash (Fraxinus quadrangulata)
  Native to parts of Missouri, including the Ozark region. While slightly more resistant than other ash species, it is still at risk if infestations are widespread.
  
  
• Pumpkin Ash and Black Ash
  Less commonly planted, but still present in wetter or bottomland areas. Both are considered highly susceptible if exposed.

Treatment and Prevention for Emerald Ash Borer

The good news is that early intervention can save healthy ash trees from Emerald Ash Borer, but timing is critical. If the infestation has already progressed too far, treatment may no longer be effective, and removal becomes the safest option. That’s why prevention and regular monitoring are so important.

Here’s how Emerald Ash Borer can be managed:

• Preventative Insecticide Treatments
  If your ash tree is still healthy or only showing minor signs of stress, professional-grade insecticide treatments can protect it. These are typically applied through trunk injections or soil drenches and are most effective when administered in early spring. Depending on the product, treatments may need to be repeated every 1 to 3 years.
  
  
• Assessment by a Certified Arborist
  Not all trees are good candidates for treatment. An ISA Certified Arborist can evaluate the health, size, and location of your ash tree to determine whether it's worth saving or if removal is the better option.
  
  
• Prompt Removal of Infested Trees
  Trees that are severely infested or already dying should be removed quickly to prevent the beetles from spreading to nearby ash trees. Safe, professional removal is key to stopping further infestation and avoiding property damage from falling limbs.
  
  
• Proper Firewood Practices
  One of the most effective ways to slow the spread of EAB is to avoid moving firewood from one location to another. Always buy and burn firewood locally.
  

• Replanting With Resistant Species
  If your ash tree needs to be removed, consider replacing it with a native or disease-resistant tree species that supports biodiversity and won’t be vulnerable to EAB in the future.