What It Means When Tiny Holes Appear On Trees (And What To Do Next)

When tiny holes appear on a tree, they often tell a story. These could either be due to harmless nesting activity of some animals, or they could be insect infestations that threaten a tree's survival. The challenge is to tell which one you are dealing with. It is essential because it is going to decide whether you should take action or let nature be. For instance, if you spot tiny D-shaped holes in your colorful autumn ash trees or a related species, it is an indication of emerald ash borer attack. These holes might appear small, but the emerald ash borer causes severe damage to the internal structure of the tree, especially the inner bark layer known as the phloem. 

Likewise, tiny exit holes with sap coming out or a sawdust-like substance known as frass point to bark beetles or other wood-boring bugs. But these pests usually only attack weak or stressed trees in your yard. In some cases, the type of tree will tell you what pest to look for based on the behavior of that particular insect. Bark beetles will attack many types of trees, but especially favor pine trees. 

Not all types of tree holes are a sign of trouble. If the holes are large, about half an inch across, and round, don't worry. These are likely the work of carpenter bees, and they are just looking for a spot to build their nests. They don't eat or damage the wood. Also, sometimes you might see tiny holes appear on trees with oozing sap. They are created by sapsuckers and may cause some stress to the plant but won't kill it.

Start with a focused inspection to narrow the cause of the holes. Don't resort to blanket treatments without a confirmed identification. Experts often recommend documenting hole size, shape, pattern, and any nearby wood debris or sap. You might also want to check the tree's shady canopy for thinning or dieback in the leaves or pine needles. The damage to the canopy often appears before holes in trees. If you suspect bark beetle damage, take a closer look under the bark as well. Note any S-shaped or serpentine larval galleries, which are a clear indication of damage from certain beetles. Sometimes a tree will have a pitch tube, a hole with sap coming out that the tree used to try to expel the pest inside. Nevertheless, your next course of action is entirely dependent on identification.

If the signs point to a benign cause, such as carpenter bee nesting, manage it with non-lethal methods. You can seal or paint the exposed wood, and for older holes, fill them with caulk or dowels. This will discourage further or re-excavation. For sap sucker damage, cover the tree trunk with burlap or tree wraps. Although temporary, it will deter repeated drilling and preserve tree health. Managing invasive beetles, such as the emerald ash borer, is trickier.

Low-value trees are often removed to prevent infestations in the nearby trees, whereas high-value trees are administered with insecticide injections or other systemic treatments. These, however, are applied by a licensed applicator. Also, do not move infested trees or firewood, as it can spread the pests and cause more damage. The most appropriate course of action in such cases is to send the evidence to your local extension service for species-specific diagnosis and regionally appropriate recommendations.