If it looks like someone stuck tiny wooden toothpicks into the trunk of your tree, take a closer look. Your tree may have some very small, very unwelcome visitors, and they’ve left their telltale calling cards behind.
Granulate ambrosia beetles (Xylosandrus crassiusculus) are tiny insects that bore into the trunks of trees and shrubs. Those distinctive strands form as females tunnel into the wood and push sawdust and other material back out through their entry holes.
For Nashville-area homeowners, that matters because granulate ambrosia beetles can target many familiar landscape trees and ornamentals, including dogwoods, redbuds, maples, flowering cherries, crape myrtles, magnolias, azaleas, and rhododendrons. Young, newly transplanted, and stressed trees can be especially vulnerable.
The good news is that spotting those toothpicks gives you a reason to investigate. Let’s look at what granulate ambrosia beetles are doing inside your tree, why some trees attract them, and what you can do next.
How Granulate Ambrosia Beetles Attack Trees
Granulate ambrosia beetles are tiny, reddish-brown insects, with adult females measuring only about 2.5 millimeters long. Originally from Asia, they were first detected in the United States in South Carolina in the 1970s and have since spread throughout much of the Southeast.
But these beetles aren’t simply tunneling into your tree for a meal.
Female granulate ambrosia beetles bore through the bark and into the wood, where they create galleries and introduce a symbiotic fungus. That fungus grows inside the galleries and provides food for both the adults and their developing young.
That unusual relationship is where the “ambrosia” part of their name comes from. It’s also part of what makes an infestation more complicated than a few tiny holes in the trunk.
By the time those distinctive sawdust strands appear outside the tree, there’s already activity happening beneath the bark.
Why Granulate Ambrosia Beetles Target Nashville Ornamentals
Granulate ambrosia beetles aren’t especially picky eaters. They can attack a remarkably wide range of trees and shrubs, including many ornamentals that are right at home in Nashville landscapes.
Dogwoods (Cornus spp.), redbuds (Cercis spp.), maples (Acer spp.), flowering cherries (Prunus spp.), crape myrtles (Lagerstroemia spp.), magnolias (Magnolia spp.), azaleas (Rhododendron spp.), and rhododendrons (Rhododendron spp.) are all among the known hosts.
But having one of these plants in your yard doesn’t mean beetles are destined to move in.The condition of your trees matters a lot.
Granulate ambrosia beetles are particularly attracted to stressed trees, and young or recently transplanted trees can be especially vulnerable. Drought, poor drainage, transplant stress, and other sources of stress may leave a tree more attractive to beetles looking for their next home.
If beetles have found your tree, identifying the infestation matters, but so does understanding why that particular tree became vulnerable in the first place.
How to Recognize a Granulate Ambrosia Beetle Attack
Those bizarre little toothpicks may steal the show, but they aren’t the only clue that granulate ambrosia beetles have moved in. Depending on the tree and the severity of the attack, you may notice several changes.
Each sign points to something different happening beneath the bark, and together they help paint a clearer picture:
- Sawdust Toothpicks: Thin, fragile tubes of frass may protrude from tiny holes in the trunk or branches. They break easily in wind or rain, so they aren’t always present.
- Tiny Entry Holes: When a frass tube breaks away, the small hole where the female beetle entered the tree remains behind.
- Wilting and Branch Dieback: The fungi associated with an infestation can interfere with the tree’s vascular system, contributing to wilted leaves and dying branches.
- Changes in Growth and Foliage: Stunted growth, delayed leaf emergence, and leaves dropping earlier than expected can also accompany an infestation.
One tricky thing about granulate ambrosia beetles is that the evidence outside the tree tells only part of the story. The galleries, developing beetles, and fungi associated with the infestation are hidden inside the wood.
Spotting an infestation doesn’t automatically tell you how the story ends.
Small nursery trees can be highly vulnerable, while death is less common in larger trees unless another stressor is also at work. That’s one reason it’s important to consider both the beetle activity and the overall condition of the tree before deciding what comes next.
Granulate Ambrosia Beetle Season in Nashville
Granulate ambrosia beetles don’t wait for summer to start house hunting. In Tennessee, adult beetles can begin emerging from surrounding wooded areas as early as February, with activity increasing during the spring.
Warm spells can get things moving surprisingly early. Overwintering females emerge and fly in search of suitable trees, where they bore through the bark, establish galleries, and begin another generation.
That makes late winter and early spring an important time to pay attention to young, recently planted, or stressed ornamentals. A tree that looked fine going into winter may suddenly develop those unmistakable frass tubes as beetle activity picks up.
And timing matters for more than spotting an infestation.
Once a female has bored into the wood, she’s protected from many treatments. Preventive management, when appropriate, depends on knowing when beetles are active rather than waiting until an infestation is well established.
Responding to a Granulate Ambrosia Beetle Infestation
Finding those little sawdust toothpicks can be alarming, but don’t assume your tree is automatically a lost cause. The right response depends on how heavily the tree has been attacked, its age and overall condition, and whether other stressors are affecting its health.
This is also a pest where timing makes a difference. Once female beetles have bored through the bark and established galleries inside the wood, insecticide options become much more limited.
Preventive treatments may help protect vulnerable trees when they’re properly timed to beetle activity, but spraying after a well-established infestation isn’t a magic reset button.
For heavily infested trees or branches, removal may be part of the recommendation. Infested wood can continue serving as a breeding site for beetles, so simply leaving severely affected material in place can create opportunities for another generation.
Before deciding that a tree needs to go, have an ISA-certified arborist evaluate its condition. A tree with a few entry points and otherwise good health is a very different situation from a young, stressed ornamental covered in active attacks.
The goal isn’t simply to get rid of a beetle. It’s to understand what’s happening with the tree, determine what can realistically be protected, and choose the response that makes sense for your landscape.
Protecting Nashville Trees From Granulate Ambrosia Beetles
You can’t hang a “No Vacancy” sign on your trees, unfortunately. But since granulate ambrosia beetles are strongly attracted to stressed trees, good tree care can make your landscape a less appealing place to settle down.
A few consistent habits go a long way toward keeping stress off your trees and beetles off your radar:
- Get Watering Right: Drought stress can leave trees more vulnerable, but more water isn’t always better. Poorly drained or waterlogged soil can stress roots, too. Aim for consistent moisture appropriate for the tree and site.
- Protect the Root Zone: Lawn equipment, construction activity, soil compaction, and other disturbances around roots can add unnecessary stress. Give the root zone some breathing room and protect trunks from mower and string-trimmer damage.
- Mulch With a Purpose: A 2- to 4-inch-thick layer of organic mulch can help conserve soil moisture, moderate soil temperature, and protect the area around the trunk from lawn equipment.
- Pay Attention After Planting: Newly transplanted trees deserve extra attention while their root systems become established. Watch their water needs and check them periodically for signs of stress or beetle activity.
- Keep an Eye on Vulnerable Trees: During periods of beetle activity, take an occasional look at young, recently transplanted, or stressed ornamentals. Catching those strange little toothpicks early gives you more information and more options.
None of these steps can make a tree beetle-proof. Reducing avoidable stress gives your trees a better chance to tolerate pest pressure and gives you a better chance of noticing trouble before it becomes severe.
Frequently Asked Questions About Granulate Ambrosia Beetles
Those tiny beetles can leave Nashville homeowners with some pretty big questions. Here are a few quick answers about what granulate ambrosia beetles mean for your trees and landscape.
Are granulate ambrosia beetles harmful to healthy trees?
They can attack apparently healthy trees, but stressed, young, and recently transplanted trees are most vulnerable. A small number of attacks on an otherwise healthy, established tree may not be fatal, so the presence of beetles alone doesn’t necessarily tell you the tree’s prognosis.
What trees do granulate ambrosia beetles attack?
Granulate ambrosia beetles have a very broad host range. In Middle Tennessee landscapes, potential hosts include familiar ornamentals such as dogwoods, redbuds, maples, flowering cherries, crape myrtles, magnolias, azaleas, and rhododendrons.
Why do granulate ambrosia beetles make toothpicks?
Female beetles excavate galleries inside the wood and push the resulting frass back out through their entrance holes. That material forms the thin, fragile tubes that look remarkably like tiny toothpicks sticking out of the trunk.
Can a tree recover from a granulate ambrosia beetle attack?
Sometimes. The outcome depends on factors such as the tree’s size and overall health and the severity of the infestation. Larger, otherwise healthy trees may tolerate limited attacks, while young or heavily stressed trees can be much more vulnerable.
Can I spray a tree after I see ambrosia beetle toothpicks?
Once the beetles have entered the wood, they’re difficult to reach with insecticides. Management is highly dependent on timing, which is one reason it’s worth having the tree evaluated.
Should an infested tree be removed?
Not automatically. Heavily infested trees or branches may need to be removed, but a few signs of beetle activity don’t necessarily mean the entire tree is lost. An arborist can evaluate the extent of the infestation along with the tree’s overall health before you make that decision.
Will granulate ambrosia beetles spread to my other trees?
They can attack multiple suitable trees in the same landscape, particularly when trees are stressed or beetle populations are active nearby. If you’ve found an infestation, it’s a good idea to keep an eye on other vulnerable ornamentals for fresh entry holes and those distinctive frass tubes.
See Strange Toothpicks on Your Nashville Trees? Let’s Take a Look
Granulate ambrosia beetles may be tiny, but the clues they leave behind are hard to miss once you know what you’re looking for. If you’re finding suspicious frass tubes, tiny entry holes, or other signs of trouble, you don’t have to figure out what’s happening to your tree on your own.
AKA Tree Service’s ISA-certified arborists can evaluate your tree, look for pest activity and underlying stress, and help you understand your options. Our pest and disease control services can help Nashville-area homeowners protect vulnerable trees and make informed decisions about the ones already under attack.
See something strange on your tree? Contact AKA Tree Service to have an expert take a closer look.
Sources & References
- Tennessee State University Cooperative Extension – “Important Ambrosia Beetle Pests of Nursery Trees in Tennessee”
A Tennessee-specific resource covering granulate ambrosia beetle identification, biology, host plants, damage, monitoring, and management.
https://www.tnstate.edu/extension/documents/Ambrosia%20Beetles%20Important%20to%20Tennessee%20Nurseries.pdf - University of Tennessee Institute of Agriculture – “Granulate Ambrosia Beetle: Xylosandrus crassiusculus”
A Middle Tennessee-focused IPM resource covering host plants, seasonal activity, toothpick-like boring dust, tree susceptibility, and management.
https://utia.tennessee.edu/publications/wp-content/uploads/sites/269/2023/10/W289-P.pdf - University of Georgia Integrated Pest Management – “Granulate Ambrosia Beetle”
An Extension pest profile covering granulate ambrosia beetle biology, susceptible ornamentals, characteristic toothpick damage, tree stress, and management considerations.
https://ipm.uga.edu/2025/10/06/granulateambrosiabeetle/ - Clemson Cooperative Extension Home & Garden Information Center – “Granulate Ambrosia Beetle (Xylosandrus crassiusculus)”
An Extension resource detailing frass tubes and other infestation symptoms, effects on tree health, vulnerable plants, and management considerations.
https://hgic.clemson.edu/factsheet/granulate-ambrosia-beetle-xylosandrus-crassiusculus/
