Insect borers are structural pests that live in trees and shrubs, causing aesthetic and economic damage. What these tiny, but damaging, pests do is tunnel through the inside of the tree, eating away until the tree becomes vulnerable and weakened. By the time the signs of an infestation are noticed, it may be too late.
Trees that have already been weakened by disease are more susceptible to infestations, which is why most species of borers are called “secondary pests.” Other borers are “primary pests” and will attack even healthy trees and shrubs. Still, a healthy tree stands the best defense against borers.
Let’s take a look at the various types of insect borers, which can help you make an informed decision when it comes to maintenance and treatment for infested trees.
Dogwood borers attack flowering dogwoods and will affect different areas depending on the age of the tree. Young trees are generally affected around the main trunk, while older trees will have signs of damage on the main limbs. Signs of an infestation include dying branches and sawdust around the cracks. Dogwoods that are planted in the sun are more susceptible than those in the shade.
Lilac borers attack lilac and ash trees, with most infestations occurring from the root crown and up 3 feet. Borers burrow into the stems of lilac trees and chew through them, leaving holes that weaken the branches. Infested branches should be cut off and discarded to protect the remaining parts.
Banded Ash Borer
Banded ash borers use only ash trees as their hosts, preferably green ash. They are aggressive and attack the trees from the ground up. Banded ash borers are similar looking to lilac borers, but they are common during the months of August and September instead of the spring months.
Peach, plum and cherry trees are all vulnerable to peachtree borers. These pests prefer young trees, as they can feed from under the bark and into the root crown. Young trees are under more threat since they can be completely infested by the borers while older trees may survive, but produce considerably less fruit.
This type of borer attacks rhododendrons as well as mountain laurel and flowering azaleas. Twigs and branches are the most at threat during an infestation, as these are the parts that the borers prefer. Other signs of an infestation include branches and twigs that have fallen off and leaves that have turned brown.
Flatheaded borers were given this name because of their flat heads. They are fast moving and can work fast from the inside of the tree and out. Infestations are difficult to identify because flatheaded borers do not expel sawdust. Instead, they pack the sawdust into their tunnels. When the adults emerge, they leave behind the telltale D-shaped holes, and the bark will become cracked.
Bronze Birch Borer
Within the flatheaded borer family, there are bronze birch borers and flatheaded appletree borers. Bronze birch borers are aggressive and severe, affecting white or paper birch trees. The early symptoms include sparse foliage preceded by twigs and branches dying off. These trees can be under attack for years and will eventually die from the infestation.
Flatheaded Appletree Borer
Flatheaded appletree borers are what attack landscape trees, so you may already be familiar with this type of pest. Flatheaded borers go after crab apples, hawthorns and red maples. There are certain types of trees that are more at risk for an infestation, most notably, newly planted trees and weakened trees. Trees that have been stressed by mechanical injury, drought or sun scald require additional care, as well as trees that are young and have just been planted.
Borers are stubborn, destructive pests, but the best defense is a healthy and well maintained tree. By keeping your trees and shrubs strong, they resist infestations in most cases. However, it is possible for even healthy trees to become infested, which is why it’s important to know the symptoms of borer infestations so that you can act fast.