What are the small holes that are spaced in horizontal rows across the bark in some trees? Sometimes there is a dark coloration of the bark below. What is causing this and could it harm the trees? This is the activity of sapsuckers, a species of woodpeckers that feed on the tree's sap.
Sapsuckers are migratory birds which are most prevalent during the spring and fall. They prefer maple trees, but will also feed on pecans, Bradford pears, and several others. The birds choose these trees due to the high sugar content of their sap. It composes up to 20 percent of their diet and is especially important during times of the year when other food sources are in short supply. The birds also eat insects they find on the trees.
They peck a small hole, roughly one-eighth to one-quarter of an inch in diameter and with a depth of one-quarter of an inch in the trunk of the tree. They will then use their tongue to suck up the sap. The holes are evenly spaced up, down, and around the trunk and appears as if they were drilled by a machine. Often the sap will flow down the trunk of the tree. It promotes the growth of black sooty mold. Sometimes these holes are mistaken for insects that bore into the tree trunks. However, the ones caused by insect borers are more randomly scattered throughout the tree.
The feeding activity of sapsuckers rarely causes harm to the trees. The holes they make are quite shallow. Many times trees can have hundreds of holes bored into their bark and not suffer at all. In rare cases, if the tree has been weakened due to other factors, such as drought or previous pest activity, there is a remote chance the sapsucker activity could harm the tree.
The sapsuckers are not easily deterred, so begin the necessary control measures as soon as damage is observed. Use a burlap or hardware cloth to cover the trunk above and below the area being attacked by the sapsuckers. It will keep them away from the trunk.
Also, hanging reflective objects in the trees, like aluminum foil or shiny pinwheels, will also discourage the birds since they dislike shiny or flashy objects. Leave these devices in place for a few weeks after you have noticed the activity has ceased to make sure the birds do not return. Repetitive loud noises, like a barking dog, can also scare them away.
Another method of control is smearing a sticky bird repellent onto the tree trunk. There are several types of these products that are available at most garden centers. Although this material will not hurt the birds, it will cause a tacky feel to the surface of the tree creating discomfort to the birds, thus driving them away. One important factor to remember is sapsuckers are classified as migratory, nongame birds. They are protected by the Federal Migratory Bird Treaty Act. Killing them by shooting, using toxicants or any other lethal method is illegal.
Sapsuckers are one of nature's more interesting wonders. Usually they are best left alone since they seldom pose a threat to the trees they feed on.
Timothy Daly is an Agriculture and Natural Resources Agent with Gwinnett County Cooperative Extension. He can be reached at 678-377-4010 or Timothy.firstname.lastname@example.org.