Crown Borer Management: Treatment And Control Of Crown Borers

Crown Borer Management: Treatment And Control Of Crown Borers

By: Kristi Waterworth

When your garden starts to look a little scraggly and plants begin to die, any good gardener will check them all over for clues to the perpetrator. When you find holes in the base of trunks or canes with sawdust-like material coming out, your problem is most likely crown borers. Let’s find out more about crown borer damage and control.

What are Crown Borers?

You may not realize you’re looking for crown borer information when you search Google, trying to discover the identity of the creature drilling holes in your caneberries and ornamental plants, but as it turns out, this damage is their most distinctive sign. The larvae of these clearwing moths tunnel their way into plants, eating as they go.

The life cycle of crown borer moths begins when adults emerge in June and July to lay their eggs on wounded or stressed plants, either on the bark or on leaves nearby. The larvae hatch and make their way to the crown, forming an overwintering area at the base of the plant that may have a blistered appearance.

In their first spring, crown borer larvae begin to tunnel into the plant’s crown, feeding until winter approaches, then making for the root system. After overwintering as a larvae, they return to the crown and feed ravenously. Near the beginning of the second summer, these larvae pupate for two to four weeks, then emerge as adults to start the cycle again.

Crown Borer Management

Crown borer damage can be very non-specific, causing plants to wilt or appear sickly. Often the sawdust-like frass is the only sign of what’s going on inside the crown. Adults, which look similar to black and yellow wasps, can be seen for short periods, but may not make themselves obvious in the landscape.

Because of this, control of crown borers is primarily defensive — infested plants should be removed as soon as possible to prevent the borers from spreading further. Prevent borers in new plantings by destroying wild brambles and other infected plants in the area and replanting with certified pest-free nursery stock.

Borers are often attracted to stressed plants, so proper care, water and pruning is vital to prevention. Familiarize yourself with the needs of each of your landscape plants and make sure to water them adequately as summer temperatures rise. Regular pruning and shaping to remove redundant branches and open the inside of the canopy is recommended.

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Borers are a group of insect pests that spend part of their adult or larval life stage feeding inside roots and branches, or tunneling beneath the bark or into the heartwood of many trees and shrubs. Many species of boring insects are capable of causing internal damage to a wide range of plants. As adults, they may be either beetles or clear-winged moths.

Plant injury caused by borers can be long lasting moderate to heavy infestation can cause death of the plant. Any plant can be susceptible, but it is generally believed that wood borers are secondary pests that develop because trees and shrubs are stressed, injured, or dying from other causes. Plants most susceptible to borer attack are those stressed from recent transplanting, drought, repeated defoliation, mechanical injury (mowers, grass trimmers), or other causes. (Also see plant information leaflet on bronze birch borer.)


The location of damage on the bark and the species of tree attacked aid in the identification of the insect involved. Most larvae are shallow-boring species and tunnel just beneath the bark of the trunk, branches, or twigs. Boring activity often starts a flow of tree sap or results in sawdust-like excrement (frass) which is visible in cracks and crevices. Tunneling of this type cuts off the water supply and can cause foliage to be off-color or drop prematurely, cracking of the bark, and dieback of branches and twigs. The overall health of the plant declines rapidly, often resulting in the death of the tree or shrub.


Flatheaded Borers (Beetles)

Adult flatheaded borers are generally known as metallic wood borers. They range in size from 1/3 to 1-inch long. Their bodies are flattened, oval, or elongated, and typically they have grooves on their wing covers. The larvae are yellowish- white, 1 to 2 inches long, broad and flat in the front and tapered toward the rear. Many have segmented bodies.

Females lay their eggs in bark crevices in the spring and early summer. After hatching, the larvae bore shallow tunnels packed with frass beneath the bark and sometimes into the heartwood. Their tunnels are long and winding, forming oval galleries beneath the bark. Dark, dead areas of bark, often with sap, are evidence of larval activity. A wet spot usually forms around affected bark. Many species complete their life cycle in one year, while others require 2-3 years.

The flatheaded apple tree borer (Chrysobothris femorata) is a common species that feeds on many deciduous shade and fruit trees and shrubs. Favorites include maple, oak, hickory, willow, sycamore, rose, tuliptree, and cotoneaster. Adult beetles are dark metallic brown to dull gray, about 1/2 inch long. The adult female lays eggs in bark crevices. The newly hatched larvae bore into the inner bark, forming tunnels and filling them with frass. If a plant is healthy, the larvae may be killed by sap flow. When nearly mature, the larvae tunnel into the heartwood where they pupate. Newly transplanted trees and shrubs are particularly susceptible.

Two-lined chestnut borer (Agrilus bilineatus) primarily attacks oaks. Some of the more frequently attacked species include white, red, scarlet, northern pin, black, bur, and chestnut oak. The adult beetle is slender, 1/5 to 1/2-inch long, with 2 yellow stripes along its back. Adults emerge in late May to early June, feeding on foliage. After mating, females lay eggs in small clusters in bark cracks and crevices. Eggs hatch in 7 to 14 days. Larvae burrow through the bark, constructing galleries tightly packed with frass. These feeding galleries cut the flow of food and water in the plant’s vascular system, causing bark to crack and split. Larvae pupate in the outer bark in a pupal cell. The following spring the adult beetle chews a D-shaped emergence hole, similar to bronze birch borer. There is one generation per year. Attacks from two-lined chestnut borer begin in the crown of a tree and proceed downward in each succeeding year of infestation.

Honey locust borer (Agrilus difficilis) attacks large and small honey locust trees, as well as branches more than 2 inches in diameter. Trees under stress are more susceptible. Adults are 1/2 inch elongated beetles, with a metallic, greenish-black abdomen with a distinct yellowish- white band on the sides. Adults emerge in June and feed on honey locust foliage. Females lay eggs that are covered with a frothy substance that hardens. The larvae bore into the trunks or branches causing sap to ooze at the site. Once exposed to air, this sap hardens into a mass of gum. Fully-grown larvae are flat and segmented. Repeated infestations gradually cause decline and dieback of twigs and branches in the crown.

Roundheaded Borers (Beetles)

The adult roundheaded borers are also known as “longhorned” beetles because of their long antennae. They have hard-shelled bodies that are sometimes colored with stripes, bands, or spots. Body length varies from 3/4 inch to over 3 inches. The larvae are white to yellow, have no legs, and are round and fleshy. Females lay eggs under bark scales, in crevices, or in tree wounds. After hatching, the larvae feed beneath the bark for a while before entering the wood. Some species do not tunnel into wood. Life cycles can vary from several months to several years.

The locust borer (Megacyllene robiniae) is a serious pest of black locust (Robinia pseudoacacia). It does not attack honey locust (Gleditsia spp.). Larvae tunnel into a tree’s trunk and branches, weakening the tree and making it susceptible to wind breakage. The most obvious sign of attack is a knotty swelling on the trunks, many broken limbs, and irregular holes.

The adult locust borer is a slender, “longhorned” beetle, about 3/4 inch long, with reddish legs and black antennae. Bright yellow bands circle its jet-black body. A distinctive W-shaped band extends across the wing covers. Often the brightly colored adults are found feeding on pollen of goldenrod (Solidago spp.) during September. Egg laying occurs in late August through October in bark cracks and scales of host trees. Eggs hatch in 7 days and small, white larvae tunnel into the inner bark causing sap to ooze around small holes. Through the spring and early summer, larvae enlarge in their tunnels. By late July into August, they have completed pupation and emerge as mature beetles.

The roundheaded apple tree borer (Saperda candida) takes 2-3 years to complete its life cycle. Adult beetles are 1 inch long and brown, with two white longitudinal stripes on its back. Larvae overwinter in various stages feeding on sapwood and heartwood. Pupation occurs in late spring of the second year, and emergence begins in early summer.

The presence of piles of frass at the base of trees or on bark of larger branches is evidence of attack. Trees become weakened and heavy infestations can kill a tree in one season. Members of the rose family are favorite hosts of the roundheaded apple tree borer.

Clearwing Moth Borers

Lilac borer

Podosesia syringae is a clearwing moth with a chestnut, brownish-black body. The forewings are dark brown and hindwings are clear with brown borders. An overwintering larva is creamy-white with a light brown head. It produces extensive holes and lateral tunnels in the sapwood of lilac, ash, privet, and other members of the olive family. The area around the holes is swollen, bark is cracked and broken, and oozing sap is mixed with sawdust and frass. Branches are severely weakened at the feeding site and sometimes break. Adults emerge in mid-spring to deposit eggs in cracks and loose bark.

Peachtree borer

Synanthedon exitiosa is a dark blue clearwing moth with yellow or orange markings. Both wings of the male are clear and there are several yellow bands on its body. The female forewings are covered with metallic blue scales and an orange band is on the abdomen. The yellowish-white larvae have brown heads and overwinter at the base of trees and in leaf litter. Pupation begins in the spring and adult emergence takes place from mid-June to late September. Adult flying, egg laying, and hatching of the two peach tree borer species overlap. Purple sand cherry (Prunus x cistena) is highly susceptible to peachtree borer.

Lesser peachtree borer (S. pictipes) adults have clear wings and metallic blue bodies with yellow markings. It is a pest of flowering cherry and almond. Larvae feed on branches, near or in trunk crotches, and at old trunk wound sites found above ground level. An amber-colored gum (gummosis) is frequently found where borers have attacked.


Trees and shrubs of low vigor or in a weakened state of health are especially susceptible to borer attack. Prevention is the key in controlling wood-boring insect pests. Keep plants healthy and vigorous.

  • Grow only trees and shrubs that are adapted to the area and site, and select resistant varieties.
  • Keep plants healthy and vigorous through proper planting, mulching, watering, fertilizing, pruning, and winter protection practices.
  • Protect trees from injuries to roots and trunks.
  • Remove dead limbs or trees promptly to avoid infestations. Remove bark from felled trees if stored for firewood.

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Here in the PNW we have two types of cane borers--rose cane borers and raspberry cane borers. Rose cane borers are mostly annoying. They kill the top inch or two of the rose cane but new growth will emerge further down the cane and the rose will be fine. Some people will seal the cane but those of us who have lots of roses don't bother--it takes too much time!

Raspberry cane borers are a differant matter. They will burrrow all the way down the cane and even into the crown of the plant and maybe kill the rose. Since you say your rose was killed I'm guessing that this is what you have. The good news is that roses are not the prefered food of raspberry cane borers--they prefer raspberries and if they can't get them they go for blackberries. If you have them on your roses it is usually a sign that somewhere in your neighborhood someone has taken out their raspberries or taken out blackberries and the hungry critters ate your roses. After a few years the cane borers will either die out or the raspberries or blackberries will come back and they will go eat those.

In the meantime, you can control the borers by keeping an eye on your roses and if you see dieback on the canes below two inches, cut back the cane to below the dieback. You will see a catapillar-ish looking thing at the bottom of the tunnel. Dispose of it. The good news is that since these critters have a one year life cycle, once you have disposed of them, they will not come back for a year. I don't know if a systemic insecticide will work. Systemics cannot be used on edibles and since this is mainly a pest of raspberries, the insecticides will not be labeled for use on raspberry cane borers. But they might work for raspberry cane borers on roses. But it is probably less work to just cut them out when you see them rather than spraying.

How to Get Rid of Peach Tree Borer

Natural and Organic Solutions

To eliminate peach tree borers without worrying about safety and toxicity, the following are some of the solutions that will deliver a high level of effectiveness.

  • Pheromone trapping can prove to be promising. This targets male peach tree borer. The trap will emit a scent that is similar to the smell of the female peach tree borers. This is also a good way to monitor their presence, providing you with an idea if it is about time to resort to more effective methods.
  • Biological controls will also deliver a high rate of success. You can introduce natural predators in the area where there are trees affected by the pest. You have the option to purchase these predators or you can also make the environment more attractive for them, such as through growing flowering trees. Some of the natural enemies of peach tree borers include parasitic nematodes and braconid wasps. The good thing about them is that they target only the pest and not insects that do not pose any harm. It will also be good to have birds, such as woodpeckers, which will eat the larvae.
  • As an alternative to chemical pesticides, there are also natural sprays that you can use. One of the best would be a spray that makes use of citrus extract. Spraying it on the bark will prevent the adults from laying their eggs. If they are already in their larval stage, however, it will be too late. Using an organic neem oil is also effective for neutralizing the eggs.
  • Another method that will work is the use of Bacillus thuringiensis. The latter is a soil bacteria that will kill the larvae, preventing it from causing damage to the host plants. Make sure to first clear the frass from the holes where you will spray it.

Chemical Solutions

Despite the apparent toxicity of chemical solutions for controlling peach tree borer, it remains to be a popular solution, especially in large plantations and when the infestation is severe. With this, some of the most popular chemical sprays include Endosulfan, Asana XL, and Warrior. To make them effective, it is important to spray directly on the bark of the tree and be sure to cover the entire area. Pay attention to the instructions from the manufacturer, especially with regards to the best time to spray.

Peachtree Borer – 5.566

Quick Facts…

Figure 1: Gumming produced at the base of a tree due to wound by a peachtree borer larva. Photograph courtesy of James Solomon, USDA Forest Service
Figure 2: Peachtree borer larvae in roots of a peach. Photograph courtesy of Eugene Nelson, Colorado State University.
Figure 3: Peachtree borer larva in the base of a peach.
Figure 4: Peachtree borer eggs. Photograph courtesy of Ken Gray Collection, Oregon State University
Figure 5: Pupa and pupal cocoon of a peachtree borer.
Figure 6: Pupal skins extruding from base of a tree after adult emergence. Photograph courtesy of David Shetlar, Ohio State University
Figure 7: Peachtree borer, adult male.
Figure 8: Peachtree borer, adult female. Photograph courtesy of David Leatherman.
Figure 9: Peachtree borer males attracted to a trap baited with a sex pheromone lure.

Peachtree borer (Synanthedon exitiosa) is the most destructive insect pest of peach, cherry, plum, flowering plum and other stone fruits (Prunus spp.) in Colorado (Figure 1). The grublike larvae chew underneath the bark at the base (crown) of the tree and on larger roots, habits that lend it another common name “peach crown borer” (Figure 2). The gouging wounds they produce can be quite extensive and may seriously weaken and even kill trees, but may not be obvious unless the area around the base of the tree is examined.

External evidence of peach tree borer tunneling is a wet spot on the bark or the presence of oozing, gummy sap. The sap is clear or translucent and often dark from the sawdust-like excrement of the insect. Most injuries occur along the lower trunk beneath the soil line. Lower branches rarely receive injuries. (Note: Oozing wounds on peach that produce an amber-colored gum may be caused by cytospora canker, a common fungal disease of stone fruits that produces symptoms that may be mistaken for those produced by peachtree borer. The presence of small particles of wood and bark within the gum distinguish damage by peachtree borer.)

Life History and Habits

The life cycle of the peachtree borer requires one year to complete. Only the immature (larva) stage (Figure 3) produces the damage to trees. Upon hatching from the eggs (Figure 4), young larvae immediately tunnel into the sapwood of the tree, usually through cracks and wounds in the bark. Larvae continue to feed and develop until the onset of cold weather. Most activity occurs a few inches below ground on the trunk and larger roots. The insects spend the winter as partially grown larvae below ground under the bark.

With the return of warmer soil temperatures larvae resume feeding and most injury is produced in mid-to late spring as the larvae mature. The larvae finish feeding and change to the pupal stage in late May through early July. Pupation occurs in a cell made of silk, gum and chewed wood fragments, located just below the soil surface (Figure 5).

The adults emerge within a month and in the process often will pull out the pupal skins, which may be then be seen around the base of the trunk (Figure 6). Adults of the peachtree borer (Figures 7, 8) are a type of “clearwing borer” moth that resemble wasps, but they are harmless and incapable of stinging. Unlike most moths peachtree borers (and other clearwing borers) fly during the day time.

The first adults, males, may emerge in as early as mid-June. However, females usually follow by a couple of weeks and most adult activity – mating and egg laying – occurs during July and August. During this time the female moths lay eggs on the bark of the lower trunk and in soil cracks near the tree base. Eggs generally hatch in about 10 days.

Preventive Sprays

Peachtree borer is most easily controlled by sprays of insecticides applied to the lower trunk and base of the tree. These are preventive sprays that target the eggs and early larval stages exposed on the bark of the tree. Once larvae have migrated into the tree, insecticides are not effective.

Depending on seasonal temperatures one can expect peachtree borer to begin laying eggs in very late June or early July. Most all eggs will be laid during July and August, although a few adults may still be present into September.

A way to best determine when adult peachtree borers are locally active is through use of traps. Various designs of traps, usually with a sticky bottom, are used and all capture adult males. These are lured into the trap by a chemical (sex pheromone) that mimics what female peachtree borers use to attract mates (Figure 9). Such traps can give one an idea of when adults are present, which is associated with periods when eggs are being laid.

In the absence of using these traps, as a general guideline, preventive trunk sprays should be applied around the first week of July. Where large numbers of peachtree borers continue to be active later in summer it may be useful to make a second application in early August.

To be effective as a preventive spray, the insecticide must have some residual activity, allowing it to kill young peachtree borer larvae emerging from eggs for several weeks after application. Presently certain formulations containing the active ingredients permethrin (Astro, Hi-Yield 38, etc.) or carbaryl (Sevin) are the only insecticides that can legally be used backyard fruit trees, have reasonably good residual activity on bark after application, and are labeled for control of peachtree borer.

* Colorado State University Extension entomologist and professor, bioagricultural sciences and pest management. 3/02. Revised 1/18.

This pest can wreak havoc on your berry patch if left unattended, but fortunately, control is easy and you can save your berries.

As I was trimming back my raspberry canes last week, I was reminded of an issue I’ve faced in my raspberry patch for the past few years: raspberry cane borers. I initially spotted the distinctive damage of this insect in the summer of 2013, and at first, I was a bit panicked by the wilted stem tips I noticed here and there in my berry patch. However, I’ve since learned not to get too flustered by this pest.

Raspberry cane borers attack blackberry and raspberry plants. The larvae of a 1/2-inch-long, slender, long-horned beetle, the borers initially cause stem tips to wilt during the summer and early autumn.

Their damage is distinctive and appears about 6 inches below the cane’s tip. Look for two rings of punctures that circle the cane and are positioned about a half-inch to an inch apart. These rings form when the adult female beetle begins the egg-laying process in June. After creating the two rings, she lays a single egg in the area between them. The egg hatches in late summer, and the resulting larva tunnels through the cane, girdling the stem tip and causing it to wilt and eventually die. Infested stems will not produce fruit, and as the season progresses, the larva burrows farther down the cane.

The borers over-winter inside the canes, and then travel all the way down to the base of the cane the following spring, causing the entire stem to die before any fruit can mature.

I’ve discovered that controlling raspberry stem borer is best achieved by observing my raspberry patch carefully throughout the summer for the distinctive pair of circular rings below wilted cane tips. When I find one of these egg-laying sites, I prune the infested cane down a few inches below the damage and then toss this damaged stem tip (with the borer still inside) into the trash or the fire pit. If the infestation becomes severe—which it seldom does—your best bet is to prune all the canes clear back to the ground every fall and burn or discard them. Doing so will get rid of all the borers, but it will also eliminate an early-season berry crop the following year. Eliminating any wild brambles near your raspberry patch will also help cut down on borers, as these plants may also harbor populations of the pest.

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