Occasionally homeowners will notice small holes in the trunks of landscape trees. This may not mean impending death to the tree, but it’s not good. The presence of holes usually means that an insect or woodpecker has taken an interest in your tree, and your tree may be in a state of decline.
Some things you can look for to help you determine the likely culprit are the size, number and arrangement of holes.
The size of hole may vary from very small to up to 3/8 inch or so. Very small holes in evergreen trees that are beginning to look thin and sick may indicate a type of bark borer. Slightly larger holes in deciduous trees may indicate a type of wood-boring beetle. Larger holes or large ragged holes may indicate a species of woodpecker.
The number of holes is also important. If you see just a few random holes, it may not raise quite the alarm that numerous holes would. This is rather intuitive – more holes, more insects, more damage. Unfortunately, when a tree begins a cycle of decline, it “smells” more appetizing to many of these insect invaders, who send signals to their friends, and after a time the tree is a goner.
The arrangement of holes is important. If holes are in a random pattern, and these usually are the smaller holes, an insect of some sort is likely to blame. If you have random ragged holes, it could be a woodpecker after insects in the tree, as we saw with woodpeckers after emerald ash borers when that wave of damage swept through our ash trees. However, if you have holes in a straight line, you likely have sapsucker woodpeckers.
Purdue experts John Bonkowski and Tom Creswell recently wrote an article about sapsucker woodpecker damage in the Purdue Landscape Report.
“Small holes arranged in neat, uniform rows and columns on the trunks of trees or woody shrubs are usually caused by sapsuckers, a type of wood pecker, instead of insects,” they said. “Sapsuckers (Sphyrapicus spp.), as the name implies, feed on the sap of living trees by drilling a row of shallow holes in the bark to genera “sap wells” that fill with sap and attract insects.”
“While sapsuckers feed on the insects that get trapped, they feed primarily on the sap that is exuded by the tree,” they said. “They often have preferred host species and you will often find them returning to the same tree that they have already drilled holes from a previous season to increase their size and generate fresh sap.”
The authors said that over time, as the number and size of holes increase, the damage caused can lead to girdling of branch limbs or even the trunk of the tree. “Thinner barked trees, like birch and maple, may be more susceptible to girdling and dieback due to sapsucker damage,” they said. “Typically, if the damage is limited and minor, the tree will recover and vigor is not significantly affected, but repeat injury to a specific location on a given tree can predispose the tree to infestation by insects or infection by decay fungi.”
It is illegal to kill woodpeckers because they are classified as migratory, non-game birds and are protected by the Federal Migratory Bird Treaty Act. “Management recommendations are typically designed to inconvenience or scare the birds from trees, including using sticky repellants, mylar flashing tape, aluminum foil strips, and predatory bird-mimics,” they said. “Use of a barrier, like plastic netting, hardware cloth or burlap, around injured areas can help discourage further feeding in that location, but sapsuckers may simply move to another part of the tree or to trees in the nearby area.”
The authors concluded by saying if trees are already severely damaged and a sapsucker is happy coming back to that one tree and few others, it might best to let them have it as a bribe to not attack your other trees.
Find the article referenced above, entitled, “Rows and Rows of Holes,” at https://www.purduelandscapereport.org/.