c/o: Andreas Krappweis
c/o: Andreas Krappweis

Roundheaded Borers are in my Tree – What Can I do About Them?

Roundheaded borers are pests that tend to attack mostly shade trees. They may also be referred to as long-horned borers. There are more than 1400 species of roundheaded borers, and they attack both hardwood and deciduous trees. These borers may also feast on coniferous trees, and they are especially of concern to shade trees in urban communities because of their close proximity to homes and structures.

What are the Signs of an Infestation?

With so many varieties of borers, it can be difficult to identify an infestation and know which species is responsible for the damage. Roundheaded borers tend to attack dying, weakened trees. Symptoms of an infected tree include discoloration and dying of the foliage. The leaves and flowers may also start to wilt.

Round holes approximately 3 mm wide will form in the bark. Sap may come out from the holes and pool there, leaving behind sap staining. You may also notice wood fibers or sawdust at the base of the tree or outside of the bark holes. When the adult females want to lay eggs, they leave behind cone-shaped holes to place them in.

How did Borers get into my Tree?

If you have successfully identified a borer infestation, you are probably wondering how the pests got into the tree in the first place. You may know the answer; trees that have been severely weakened from sun scald, mechanical injury or disease are especially vulnerable to borer infestations. Roundheaded borers in particular use dying, highly stressed or weakened trees as their hosts, so you may remember that the tree suffered some type of stress months or even years ago.

Another way that roundheaded borers can get into your trees and shrubs is from an infestation in a separate area. If you don’t identify the infestation early enough, it can spread to other trees in your garden. Or if you removed the tree, but didn’t take the proper measures of burning all of the tree’s contents – fallen twigs and branches included – the debris on the ground could have caused other trees to become infested.

How do I Handle an Infestation?

The best time to take control of the infestation is when the adult beetles are laying eggs on the tree trunk, but this can be difficult to pinpoint. Unfortunately, signs of an infestation may emerge but are often misdiagnosed for another type of condition or tree disease.  An ISA Certified Arborist licensed in pest control should be consulted to make a proper diagnosis and provide recommendations.

How Can I Prevent Infestations in the Future?

The best approach to any infestation is to avoid it all together. Promoting healthy tree growth, protecting trees from disease and mechanical injury and delivering adequate moisture are all effective ways to keep trees healthy and strong. Watering trees and using mulch can bring necessary moisture, and removing fallen debris and leaves from around the trunk of the tree can prevent mold and disease.

If a tree does become mechanically damaged from lawn or construction equipment, apply a wound dressing to protect the opening from disease and infection. Trees that are close to buildings and other structures are susceptible to this type of damage, so consider using cables or braces to bring additional support to the tree. Shrubs and trees should also be pruned regularly to remove branches that are split, torn or broken.

Having a healthy garden is always a work in progress, but know that healthy trees always stand a better chance against roundheaded borer infestations.