Borer prevention and control is important to the life of a healthy landscape. Borers harm trees by tunneling into their trunks and branches, cutting through the cambium layer — the part responsible for moving water and nutrients throughout the tree. When the cambium is damaged, it can cause dieback and leave the tree stressed, making it more vulnerable to other diseases. In severe cases, a borer infestation can even kill the tree.
Borers typically have four stages to their life cycle:
- Egg
- Larva/Grub
- Pupa
- Adult Moth
Depending on the species, borers usually have life cycles that range from one to three years.
Table of Contents
TL;DR: Whats a borer? And what can I do about it?
Answer:
Emerald Ash Borer
This jeweled beetle, originally native to northeastern Asia, has come to the US and spread to over 30 states. Currently in Boulder and northwest suburbs of Denver.
Host Trees
- Ash
Susceptibilities
Trees stressed by drought, disease or other borers.
Symptoms & Recognition
S-shaped galleries will be present on the inner bark, as well as D-shaped exit holes. Presence of woodpeckers may be increased. New infestations may be extremely difficult to detect, even for a few years. Vertical bark splitting can occur, as well as branch dieback on the upper crown with signs of yellow, thin or wilted foliage.
Management & Treatment
Borer Prevention
Avoid moving firewood to new areas – use local sources as much as possible. Insecticides can be utilized through direct injection by a professional. If an infestation is detected, the tree will typically be removed to reduce this borer’s population.
Benjamin Smith from United States, CC BY 2.0, via Wikimedia Commons
Notes
The six-spotted green tiger beetle is commonly mistaken for the Emerald Ash Borer.
Treatment Window
Lilac/Ash Borer
Adults are brown and black clearwing borers, similar in appearance to paper wasps. Larvae are creamy white with a dark head. Small prolegs on the grub.
Host Trees
- Lilac
- Privet
- Ash
Susceptibilities
Trees under stress, recently transplanted trees, poorly sited trees with limited root growth areas.
Symptoms & Recognition
Might be sawdust from the entrance hole at the base of infested trees. Old pupal skin is likely to be attached to the tree. Disfiguring of the trunk might occur from heavily damaged trees, as well as an increased susceptibility to branch breaks in higher wind speeds.
Management & Treatment
Borer Prevention
Preventative measures include relieving tree stresses and proper watering. Avoid pruning prior to when adults fly. Pheromone traps can be beneficial. Follow up with insecticidal sprays 2 weeks after adults are trapped.
Frank Vassen from Brussels, Belgium, CC BY 2.0, via Wikimedia Commons
Notes
One of the few types of borers that flies during the day. If the infestation is treated properly, the attack will likely not be fatal to the tree.
Treatment Window
Banded Ash Borer
The Banded Ash borer is marked with yellow or white stripes on the wings and is a roundheaded borer. Larvae are creamy white in color and have dark, round heads
Host Trees
- Ash
- Hickory
- Linden
- Elm
Susceptibilities
Dead, dying, stressed or diseased trees.
Symptoms & Recognition
Tunneling patterns will be present on the inner bark, as well as oval/round-shaped exit holes. Presence of granular frass in the tunnels.
Management & Treatment
Borer Prevention
Avoid long-term storage of firewood. Insecticides can be utilized through sprays by a professional.
Beatriz Moisset, CC BY-SA 4.0, via Wikimedia Commons
Notes
The Redheaded Ash borer is a close relative of the Banded Ash borer. The larvae are nearly indistinguishable from one another.
Treatment Window
Poplar Borer
The adults are approximately 1 1/4 inches long and grey with brown and black specks and a central yellow stripe on thorax. Black and yellow can also be present on wing covers. Larvae are young, white-yellowish grubs. About 1 3/4 inches when mature.
Host Trees
- Aspen
- Cottonwood
- Poplar
Susceptibilities
Generally large diameter trees. Unshaded trees. Growing stresses related to site.
Symptoms & Recognition
Chronically infested trees have black, varnish-like stains on the bark, along with sawdust that may pile at the base of the tree. Wound sites develop as rough growths that may split the bark. Wet spots from oozing sap mixed with boring dust or shavings are signs of early infestation, especially in clusters. The wood can become honeycombed under the bark and irregular patches of bark will fall out.
Management & Treatment
Borer Prevention
Parasites of eggs and larvae, predators and fungal diseases. Site aspen so that they’re shaded with optimal growing conditions and avoid planting at low elevation valley sites. Insecticides should be utilized in the middle of the tree, where attacked.
Siga, CC BY-SA 3.0, via Wikimedia Commons
Notes
Difficult to control due to its long life cycle.
Treatment Window
Peach Tree Borer
Adults are clearwing moths that fly during the day. Like the lilac ash borer, they superficially resemble wasps. Adult females have light, thin bands on abdomen or a broad band of orange or red, while adult males have yellow stripes.
Host Trees
- Peach
- Cherry
- Plum
- Stone Fruit Trees
Susceptibilities
Trees with wounds.
Symptoms & Recognition
Wet spots, or clear gum at wound areas mixed with wood fragments may be present. Most injuries are at/below soil line. Occasional pupal skins will occur on the soil surface.
Management & Treatment
Borer Prevention
Treatments of the lower trunk are effective before larvae migrate into the tree. Pheromones can help determine when adults are present. Moth balls/crystals can also be effective.
skitterbug, CC BY 4.0, via Wikimedia Commons
Notes
Larvae cannot be controlled with insecticides after tunnelling.
Treatment Window
Pinyon Pitch Mass Borer
Adults are brown grey with zig zag markings. Larvae are creamy white/pink with a dark head.
Host Trees
- Pinyon Pine
- Ponderosa Pine
Susceptibilities
Trees under stress, drought-susceptible trees, overcrowded pine trees.
Symptoms & Recognition
Pale pink pitch often oozes from gouges in the bark, and eggs are typically laid near existing wounds. Trees with heavy damage may develop trunk deformities and become more prone to branch breakage during strong winds.
Management & Treatment
Borer Prevention
Preventative measures include trunk sprays with insecticide. Avoid over-irrigating the landscape. Avoid pruning prior to when adults fly.
Ryan Hodnett, CC BY-SA 4.0, via Wikimedia Commons
Notes
Adults may be difficult to distinguish from Zimmerman Pine moths.
Treatment Window
Plant Health Care Experts
The most effective way to protect your trees from insect damage is through a combination of proper pruning, consistent watering, and targeted pest control.
Our Plant Health Care team is trained to spot early signs of borer damage and take action to minimize its impact. While tree loss isn’t always inevitable, it’s a risk we work hard to prevent. If you think your trees might be infested, reach out to the experts at Front Range Arborists — we’re here to help.
Borer Prevention....and More
Borers aren’t the only pests that can threaten your trees. It’s important to recognize the signs of borer damage, along with injuries caused by bark beetles and other insects.
Need More?
Interested in learning more about insects and the damage they can cause to your trees? CSU Extension offers a wide range of publications on the subject.