Bark lice on trees

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FIGURE 1. Barklice (Cerastipsocus venosus) nymphs are dark gray with pale yellow banding between abdominal segments. Adults and nymphs are gregarious and typically encountered as a colony (sometimes numbering several hundred individuals, as in the above photo taken on March 2007).

FIGURE 2. When disturbed, Cerastipsocus venosus often exhibits the fascinating behavior of temporarily scattering when suddenly disturbed, only to rejoin again as a “herd.” Not surprisingly, they are also known as “bark cattle” or “tree cattle.”

FIGURE 3. As nymphs mature to full size, they develop wings. Wings are light colored at first and quite wrinkled. Very young adults are almost white in color but assume their darker pattern of color in a short time.

FIGURE 4. Adults are about ¼ inch long and have shiny black wings, which are held in tent-like fashion over their abdomens.

Quick Facts

Common Name:

Barklice (a general term given to a diverse group of soft-bodied insects in Family Psosidae)

Genus / Species:

Cerastipsocus venosus

Size: Slightly over ¼ inch

Type of Beneficial:

Decomposer/Recycler

Type of Metamorphosis:

Immature stages similar in appearance to adults (i.e., simple metamorphosis)

Beneficial Stage(s):

Immature stages (known as nymphs) and adult stage

Diet:

Fungi, algae, dead bark, and other organic materials on tree trunks and large limbs

Occurrence:

Two barklice species occur across the Galveston-Houston region; Cerastipsocus venosus encountered but Archipsocus nomas more common

2007 . . . The Year of the Barklice—Archipsocus nomas

The calls started coming in on the Master Gardener Hotline during the mid-March 2007. Then during the last week of March 2007, several area residents submitted insect samples for identification—with each sample containing numerous small dark colored insects. The first e-mail request of the year for identification of this insect came from Rick & Lynn Vera on March 29. They provided an excellent quality image ().
While the Extension Office has been inundated with insect samples, we are gratified that area residents are becoming increasingly aware of the importance of trying to first identify insects before reaching in their chemical storerooms to engage in chemical warfare against insects.

Although based on antidotal evidence, we suspect that the educational enlightenments provided over the past few years by the Extension Office and the Master Gardeners is having an impact! The Extension Office certainly has experienced a yearly increase in the number of residents who visit the office to get help with identifying insects.

Two Species of Barklice in our Region
We have been alerted in our Master Gardener Training Course to be prepared to get calls during midsummer from homeowners who are alarmed about the appearance of mysterious webbing on the trunks of their oak trees! Fortunately, the webbing is not caused by webworms nor tent caterpillars, but by a harmless insect commonly known as barklice.
The species of barklice most commonly encountered in the Galveston-Houston region is brownish-colored and gregarious (Archipsocus nomas). Archipsocus nomas is a very small (less than 1/8 inch long) and soft-bodied insect. They live together underneath the protective layers of silken webbing. The silk webbing produced by this species of barklice typically appears in late summer (July and August). The webbing can completely envelop the trunk and large branches of a tree seemingly overnight.
The insect samples mentioned in the opening paragraph above were also determined to barklice. However, they were not small (adults are about ¼ inch long) and high populations were appearing in late March and not during the heat of summer. Although huge numbers would occur on tree trunks, no webbing was produced.

Basic Description
It turns out that this larger size barklouse is a closely related species of web-forming barklice. The scientific name of this species is Cerastipsocus venosus. Members of this species are noticeably larger than their web-forming cousins. Adults have shiny black wings, which are held in tent-like fashion over their abdomens.
Nymphs appear dark gray and pale yellow banding between abdominal segments. Adults and nymphs have round heads and conspicuous antennae. Members of Cerastipsocus venosus are also gregarious and typically encountered as a colony (sometimes numbering several hundred individuals, as in March 2007).
Each colony typically contains a mixture of nymphs and adults. As nymphs mature to full size, they develop wings. Wings are light colored at first and quite wrinkled. Very young adults are almost white in color but assuming their darker pattern of color. Adults are “reluctant” to fly but this is the primary means of dispersal {refer to Figure 4 at the bottom of the article on Barklice (Archipsocus sp.)}.

Behavior
The term “lice” as part of the common name of these tree dwellers is quite misleading as these insects are neither parasitic nor louse-like in appearance. Upon being informed of the identification of this insect, the typical response of a gardener is a widening of the eyes and other momentary indications of being aghast! Our Galveston County Extension Horticulture Agent advises us to precede the identification with a notation of “Congratulations, you have beneficial insects in your landscape!”
When disturbed, Cerastipsocus venosus exhibits the fascinating behavior of moving en masse, somewhat like a flock of sheep or herd of cattle. They may also temporarily scatter when suddenly disturbed, only rejoin again as a “herd.” Not surprisingly, they are also known as “bark cattle” or “tree cattle.” Barklice are most often noticed on smooth-barked shrubs and trees such as crape myrtle and on oaks although they occur on a variety of hardwood ornamental plants (we have seen them on Bradford pear).

Beneficial Status
You may wonder why barklice are being included as beneficial insects. As scavengers, they perform a valuable function in consuming excess accumulations of fungi, algae, dead bark and other materials that occur on tree trunks and large limbs–in effect, they function as “Bark Maids” to help clean the bark of undesirable inhabitants. Barklice do not eat leaves or the bark of the tree, nor do they damage the tree by boring into the bark.
No control measures are recommended for these insects. Treatment is not recommended as the barklice are providing a beneficial service by helping Mother Nature to keep the bark clean and tidy!

Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.

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FIGURE 1. Webbing produced by certain barklice (Archipsocus nomas) may completely envelop the trunks of trees as well as large branches. Oaks and pecan trees are most commonly affected in the Galveston-Houston region.

FIGURE 2. This silken webbing has a silvery sheen. Barklice feed on fungi, algae and other organic materials on tree bark.

FIGURE 3. Archipsocus nomas are brownish-colored insects that are gregarious and very small (less than 1/8 inch long).

FIGURE 4. Another closely related species of barklice may also be encountered in the Galveston-Houston region: Cerastipsocus venosus. (Specimen pictured above made a landing on a cap!)

Quick Facts

Common Name:

Barklice

Genus / Species:

Archipsocus nomas and Cerastipsocus venosus

Type of Beneficial:

Decomposer/Recycler

Type of Metamorphosis:

Immature stages similar in appearance to adults (i.e., simple metamorphosis)

Beneficial Stage(s):

Immature stages (known as nymphs) and adult stage

Diet:

Fungi, algae, dead bark, and other organic materials on tree trunks and large limbs

Occurrence:

Occur across the Galveston-Houston region; Archipsocus nomas is common and Cerastipsocus venosus is occasionally encountered

We have been alerted in our Master Gardener Training Course to be prepared to get calls during midsummer from homeowners who are alarmed about the appearance of mysterious webbing on the trunks of their oak trees! And, distressed homeowners generally want to know what pesticide can be used to get rid of the problem.

Fortunately, the webbing is not caused by webworms nor tent caterpillars, but by a harmless insect commonly known as barklice. It is important to understand that the common name used for these insects is misleading as they are not lice. Except for their very small size (less than 1/8 inch long), they do not even look like lice.

The species of barklice most commonly encountered in the Galveston-Houston region is the brownish-colored and gregarious Archipsocus nomas. They live together underneath the protective layers of silken webbing. The silk webbing produced by barklice typically appear in late summer (July and August). The webbing can completely envelop the trunk and large branches of a tree seemingly overnight. Its appearance may be associated with long periods of high humidity.

Barklice are small soft-bodied insects resembling aphids. Their web provides protection from predators while allowing the insects to feed. Although it gives the tree a “ghostly” appearance, the silk webbing–as well as the insects–are harmless and will disappear during the onset fall weather. Barklice live on the rough bark of hardwood trees, particularly live oaks and oftentimes on pecans.

Another closely related species of barklice may also be encountered the Galveston-Houston region: Cerastipsocus venosus. Members of this species are noticeably larger and less commonly encountered than their web-forming cousins. Adults are about 1/4 inch long and have shiny black wings, which are held in tent-like fashion over their abdomens. Members of Cerastipsocus venosus are also gregarious and typically encountered as a colony.

You may wonder why barklice are being included as beneficial insects. As scavengers, they perform a valuable function in consuming excess accumulations of fungi, algae, dead bark and other materials that occur on tree trunks and large limbs–in effect, they function as “Bark Maids” to help clean the bark of undesirable inhabitants.

Barklice do not eat leaves or the bark of the tree, nor do they damage the tree by boring into the bark. Although they may be viewed as unsightly, they are short-lived and harmless.

No control measures are recommended for these insects. Treatment is not recommended as the barklice are providing a beneficial service by helping Mother Nature to keep the bark clean and tidy!

Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.

Webbing on an Oak Tree
(Click to Enlarge)
Photo by Tom MacCubbin
What many gardeners are seeing resembles a Halloween horror tour but it’s not October and this is in their own yards.
Their tree and some large shrub limbs are covered with a webbing that resembles a stocking. It’s a bit scary as in the picture sent by one of our local gardeners.
Do put your mind to rest this is not the horror show many feared and it’s not a major problem either. The webbing is the handy work of psocids also known as tree cattle and bark lice. They do not affect you and they don’t affect the tree either. These are small leaf-hopper looking insects that move about in clusters or herds. The only feed on bits of old bark, lichens and algae.
What they are really up to is raising the next generation within the very protective webby covering. Their spinnings may cover major and small limbs but almost never envelops plant foliage. The webbing cannot suffocate the trees as many fear.
Most likely the web will disappear with the next rain or if you want you can wash it off. There is no need to use pesticides and the insects cause no harm. Just enjoy their handiwork.

Contents

What is this white fungus on my oak tree?

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Insect Borers of Trees and Shrubs

ENT-43: Insect Borers of Trees and Shrubs | Download PDF

by Daniel A. Potter and Michael F. Potter, Entomologists
University of Kentucky College of Agriculture

Wood-boring insects are among the most destructive pests of ornamental trees and shrubs. Most borers are the larvae (immature stages) of certain moths and beetles. They tunnel and feed under the bark in living wood, destroying water- and sap-conducting tissues. This causes girdling, branch dieback, structural weakness, and decline and eventual death of susceptible plants. Infestation sites also provide entry points for plant pathogens.

Clearwing and flatheaded borers are the main types that attack woody ornamentals. The groups differ somewhat in their habits and host preferences, which can affect the approach for controlling them with insecticides. The keys to controlling these pests are to keep plants healthy and, if necessary, to treat during those times of the year when the insects are vulnerable to insecticides.

Infestation and Damage

Borers rarely infest healthy plants growing in their natural environments. However, when trees or shrubs are transplanted into the landscape, stresses such as drought, soil compaction, sun scald, or injuries can weaken them and make them more susceptible to attack. Adults may locate suitable egg-laying sites by responding to volatile chemicals that emanate from stressed trees.

Adult borers emerge from infested trees in the spring or summer. After mating, the females fly to a suitable host and lay eggs on the bark, often in crevices or around wounds. Hatching occurs about 10 days to 2 weeks later. The young larvae quickly tunnel beneath the bark where they feed and grow. Once inside the tree, borer larvae are no longer vulnerable to insecticide sprays and are seldom detected until serious damage has been done.

Several species of clearwing and flatheaded borers can infest landscape plants. While some are attracted to a range of hosts, most attack only certain kinds of trees and shrubs. It is important to know when the adults of each species are active and which plants are vulnerable in order for treatment to be effective.

Clearwing Borers

Adult clearwing borers are delicate, day-flying moths that resemble small wasps. The moths feed only on nectar or not at all so they do not cause damage. The larvae are whitish, hairless caterpillars with brown heads. The most damaging clearwing borers are associated with dogwood, lilac, ash, oak, rhododendron, and ornamental Prunus species, including flowering peach, plums, and cherries.

Detecting Clearwing Borers

Early signs of clearwing borer infestation are wilting of terminal shoots, and branch and crown dieback. Infestation sites often are marked by cankers, calluses, or cracked bark. Large limbs may die or become so weakened that they are easily broken in the wind. Established trees may persist in poor condition and be re-infested year after year.

Clearwing borers expel coarse, brown frass (sawdust-like fecal material) from cracks in the bark. In some hosts, especially Prunus species, the frass may be mixed with oozing sap or gum. When the adult moth emerges, it leaves an empty, tan shell (pupal skin) that protrudes from the bark. Feeding holes left by woodpeckers or other birds may indicate that a tree is infested.

Figure 1a. Symptoms of clearwing borer infestation include crown dieback

Figure 1b. Coarse, sawdust-like frass exuding from cracks in the bark from clearwing borer.

Insecticides for Clearwing Borers

Properly-timed bark sprays with contact insecticides can prevent infestation of susceptible trees and shrubs. Pyrethroids including bifenthrin (Onyx®, (Talstar®) and permethrin (Astro®) work well. Chlorantraniliprole (Acelepryn), is an effective, bee-friendly option. Chlorpyrifos (Dursban® 50W) can still be used in commercial nurseries. All of those products are contact insecticides that require proper timing in order to intercept newly hatched clearwing borer as they crawl over or tunnel into the bark. The trunk and main scaffold limbs should be sprayed to runoff but the foliage need not be sprayed.

Systemic insecticides, whether applied as injections or as soil treatments, generally have not given reliable control of clearwing borers.

Application Timing for Clearwing Borers

Table 1 includes a list of approximate treatment dates if spraying bark to protect trees from becoming infested by clearwing borers. These timing guidelines are based on several years of monitoring borer flight periods in Kentucky. These are average target dates; the best timing may vary from year to year depending on spring temperatures (i.e., earlier in warmer years, later in cool ones). Because plant and insect development are both temperature-dependent, using plant phenology (seasonal timing and sequence of bloom of so-called “indicator plants”) is often a more accurate scheduling tool than relying on calendar dates. Indicator plants whose blooming coincides with spray timing for particular borer species are listed in Table 1.

Sticky traps baited with lures containing synthetic sex pheromones are another way to fine-tune spray scheduling for borer control. These lures mimic the scent produced by the virgin female moth when she is ready to mate. Male moths detect the airborne scent from a considerable distance, and they follow the chemical trail upwind to its source. Hang the trap in a convenient tree or shrub in early spring, and check it weekly until flight begins. Apply your spray 10 to 14 days after the first males are caught, which will coincide with the beginning of the larval hatching period. This provides a protective residue that intercepts the young borers before they can tunnel through the bark. Apply a second spray if males are still being captured after 6 weeks.

Commercial trap kits come with several cardboard traps, instructions, enough bait to last a season, and picture keys for distinguishing the various captured borers. Some borers respond to particular baits, so when ordering traps, specify the borer or tree species that concerns you. Trapping does not increase risk of infestation because only males are attracted.

Types of Clearwing Borers

Dogwood borer, Synanthedon scitula, prefers flowering dogwood (Cornus florida) as its host. Infestations in young trees usually occur in the main trunk, often around lawn mower injuries. Infestations in older trees are likely to be higher up in limb crotches or main limbs and associated with pruning scars, cankers, or cracked bark. Dogwood trees planted in the sun are more susceptible than trees in the shade. Symptoms include dieback of branches and coarse, sawdust-like frass expelled from cracks in the bark. This insect species is widely distributed wherever dogwoods are cultivated.

Lilac borer, Podosesia syringae, is a pest of lilac, ash, and privet throughout the United States east of the Rockies. Most infestations occur from the root crown up to about 3 feet. This species begins to fly in late April or May.

Banded ash clearwing borer, Podosesia aureocincta, attacks only ash, especially green ash (Fraxinus pennsylvanica). The adults resemble lilac borers and may be monitored with the same pheromone lures, but they are active in August and September—well after the lilac borers’ flight is finished.

Peachtree borer, Synanthedon exitiosa, and lesser peachtree borer, Synanthedon pictipes, are pests of peach, plum, cherry, and other Prunus species, including both fruit and ornamental varieties. Peachtree borer larvae attack mainly young trees, feeding under the bark from the root crown to about 2 feet above ground level. The lesser peachtree borer prefers older trees, infesting the upper trunk and main branches, often around wounds, cankers, or other damaged areas. Infestation sites are marked by accumulations of brown frass mixed with sap and gum.

Rhododendron borer, Synanthedon rhododendri, attacks rhododendrons and, occasionally, mountain laurel and flowering azaleas.

Figure 2a. Clearwing borer moths, such as this banded ash clearwing borer, resemble a stinging wasp.

Flatheaded Borers

Adult flatheaded borers are fast-moving, flattened, metallic-colored beetles with short antennae. Larvae are whitish, legless, and the first segment of their thorax is wide and flat just behind the head. They make winding tunnels beneath the bark, destroying phloem and cambium and girdling the trunk or branches. The tunnels may be visible externally as spiral ridges or cankers on the limbs or trunks. Unlike clearwing borers, which expel frass from cracks in the bark, flatheaded borers pack their fine, sawdust-like frass in their tunnels.

Figure 2b. Flatheaded borer adults, such as this bronze birch borer, are beetles
(Photo: Steven Katovich, USDA Forest Service, Bugwood.org)

Symptoms and Diagnosis of Flatheaded Borers

Adults emerge from infested trees in spring or summer through characteristic D-shaped holes. With some species (such as the flatheaded appletree borer), the bark becomes cracked or cankered at the site of attack. After mating, female borers emerge and lay their eggs on the bark of their preferred host trees. Unlike young clearwing borers, newly hatched flatheaded borers do not crawl over the bark in search of entry points. Instead, they chew directly into the tree through the bottom of the egg shell. Besides the D-shaped holes, symptoms include thinning and dieback of branches, usually starting in the upper 1/3 of the tree canopy, followed by eventual death of the tree.

Controlling Flatheaded Borers

Systemic insecticides applied via trunk injection, basal bark sprays, or as a soil drench are effective against flatheaded borers and they may be the only practical method for treating tall trees. Newly-transplanted ornamentals and nursery liners can be protected with properly-timed bark sprays of the same types of pyrethroids listed above for clearwing borers.

Types of Flatheaded Borers

Emerald ash borer (Agrillus planipennis) adults are distinctive dark metallic green beetles that are about 1/2 long and about 1/8 inch wide. This invasive insect, which has killed hundreds of millions of ash trees in North America, was discovered in Kentucky in 2009. The larvae feed on the inner bark of ash trees from June through October, disrupting the tree’s ability to transport water and nutrients. Unless protected, infested trees usually die within 4 to 7 years of attack. All native ash species are susceptible to attack. The insect has been found recently in white fringetree (Chionanthus virginicus).

Ash trees can be protected from attack by this devastating insect by: 1)a systemic insecticides applied by soil injection or soil drench (dinetofuran, imidacloprid), 2) systemic injections applied as trunk injections (azadirachtin, emamectin benzoate, imidacloprid), or 3) a systemic insecticide applied as a lower trunk spray (dinetofuran). Options vary with tree size (diameter at breast height). Homeowners may use products that contain either dinetofuran or imidacloprid). See Insecticide options for protecting ash trees from emerald ash borer for detailed information on control options:

Bronze birch borer (Agrilus anxius) is a severe pest of white or paper birch in the landscape. Symptoms include twig and branch dieback starting in the upper 1/3 of the tree. With successive years of attack, the tree becomes progressively weaker until it is killed.

Dead or dying limbs will have numerous D-shaped adult exit holes, each about the size of a BB shot. Adult bronze birch borers are slender, olive-bronze beetles about ½-inch long. In Kentucky, adults begin emerging and laying eggs in mid-May.

The flatheaded appletree borer, Chrysobothris femorata, is a severe pest of small, stressed landscape trees, especially flowering crab apples, hawthorns, and maples during the first year or two after they are transplanted. This borer may attack almost any hardwood tree that is stressed by defoliation, sun scald, drought, soil compaction, or mechanical injury. It makes broad winding tunnels under the bark, destroying the phloem, cambium, and outer xylem. The full-grown larva is about an inch long, legless, and yellow-white. A single borer can girdle and kill a small tree.

Figure 3. The flatheaded appletree borer larva makes winding tunnels beneath the bark, destroying the phloem, cambium, and outer xylem and girdling the trunk of young trees.

The adult beetle is flattened, about ½-inch long, bronze-colored above, and brassy underneath. It leaves a large, 3/16-inch, D-shaped hole when it emerges from the tree. The adults emerge and begin to lay eggs in late May or early June in Kentucky.

Figure 4a. Symptoms of bronze birch borer attack include crown dieback

Figure 4b. D-shaped holes left by the adult bronze birch borer beetles as they emerge from limbs or trunks.

Preventive Management for Borers

Stressed trees and shrubs tend to be more susceptible to borer infestation, so plant health care is a first line of defense:

  • Do not plant ash trees; because of emerald ash borer it is no longer a suitable landscape plant.
  • Avoid planting native understory species such as dogwoods and rhododendrons in full sun.
  • Select well-adapted cultivars for your region.
  • Use proper planting methods. Transplanted trees and shrubs need extra water until they become established.
  • Control other pests that contribute to tree stress.
  • Be careful not to wound the bark when mowing or using a string trimmer. Fresh trunk wounds are attractive to egg-laying adult borers.
  • Avoid tree wraps – they may encourage borer attacks by delaying proper hardening of the bark.
  • Inspect susceptible tree species regularly for the telltale symptoms, and apply insecticides only during those periods when borers are vulnerable.

Mention or display of a trademark, proprietary product or firm in text or figures does not constitute an endorsement and does not imply approval to the exclusion of other suitable products or firms.

Revised: 4/16

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!

Images: Dan Potter, University of Kentucky Entomology except bronze birch borer adult: Steven Katovich, USDA Forest Service, Bugwood.org

Tree Borer Management: Signs Of Tree Borer Insects

Landscape trees burst to life in the spring, sprouting flowers in almost every color and young, tender leaves that soon expand to create puddles of shade on the lawn. But would you know how to identify tree borers if your trees didn’t behave predictably one spring? Keep reading to learn more about how to identify tree borers and treatment for tree borers once this becomes an issue.

What are Tree Borers?

Tree borers are a group of insects that lay their eggs on or inside of trees, where the young larvae eat their way through living tissues. These miscreants can be either beetles or clearwing moths, but the end result is the same. Tree borer insects cause affected parts of trees to slowly weaken as their chewing severs vital transport tissues. Over time, they may girdle trees or weaken branches to the point that they break under pressure.

The most obvious signs of tree borer insects are the tiny holes they cut into trunks, branches and stems. These holes may be perfectly round or slightly oblong, sometimes a sawdust-like material, called frass, falls on branches below these holes or forms a long cylinder as tree borer insects excavate tunnels.

Tree Borer Management

Treatment for tree borers can be difficult if adults are already present and laying eggs throughout the tree. Trees with many holes bored through the trunk are often easier to replace than to successfully treat, since the internal damage can be extensive after just a few seasons. Prevention is key if your trees are unaffected, but tree borer insects are active nearby.

Trees that are not infested, or have only a few noticeable holes, may be protected from borers by improving care. It may seem too easy, but borers are attracted to trees that are stressed and injured; pruning wounds are a common entry point for the first generation of invading borers.

Adding mulch around your tree and providing it with supplemental water and fertilizer will help it fight off borers and heal from previous damage.

Chemical Control of Borers

Trees that are riddled with borer holes are past the point of saving. These trees must be removed for safety’s sake; galleries can extend several inches past the penetration point, weakening limbs and branches that may snap with the first strong gust of wind. You must burn or otherwise destroy the infected tree’s tissues as soon as possible to prevent any borers that remain from escaping to nearby trees.

Chemical treatments are available for trees with minor infestations, though they generally are aimed at preventing re-infestation. Residual insecticides like carbaryl, chlorpyrifos, lindane and permethrin are designed to remain on tissues for many weeks, so that any insect that comes in contact with them will die immediately. All woody surfaces must be covered for these materials to work.

Imidacloprid and dinotefuran, systemic insecticides, can control borers that remain close to the bark layer of the tree, but should not be applied without identifying the pest inside your tree first. Sticky traps or pheromone-baited traps can be helpful in this department, but don’t rely on these traps to provide control for your borer problem.

What Causes Tiny Rows of Holes in Tree Trunk (Maple, Oak, Apple)?

Shaggy, smooth, papery–tree bark comes in all sorts of textures and shades. But no matter its appearance, that bark’s not just there for looks!

A tree’s outermost layer of bark protects it from outside stressors, like extreme temperatures, insects or pecking birds. So, when intruders break through the bark, it can be bad news for the tree.

Michelle, a Davey blog reader from New Jersey, saw this first-hand on her evergreens. She wrote, “The spruces in my front yard are becoming see-through with a lot of dead, bare branches. They have little holes in the main trunk, and the sap has dripped out. What is wrong with them?”

Read on to find out the top reasons why there are holes in your tree’s bark, like Michelle’s tree.

Do tree insects cause holes in tree trunks?

Certain pests, called borers, tunnel their way in, out, and around tree bark–and even the wood under bark! All that movement may leave behind teeny, tiny holes.

But they’re not the only culprits! Birds can do it, too.

So, who’s decorating your tree with their distinctive mark? The size and distribution of the holes will help you narrow it down.

What causes tiny holes in tree trunks?

  • Who done it: Marks as thick as a piece of spaghetti are often left by bark beetles or similar borers. There are tons of species. Most of them seek out weak trees that are stressed by environmental stress, improper watering, pruning injuries or other insect attacks.

  • What they do: These pests tunnel into the tree and lay eggs. Then, young borers chew through the tree, which disrupts its ability to transport food and water. That can kill the tree. Once the beetles grow up, they exit the tree, leaving a series of tiny holes as proof.

  • Other symptoms: Bark beetles often leave sawdust or little tubes of sap on the trunk as well. From there, look for browning foliage as well as early leaf or needle drop. If you think you have beetles or borers, act quickly.

  • What to do next: You can proactively treat for some borers (like emerald ash borer) and beetles (like pine bark beetles). But once you spot advanced symptoms, you often need to remove the tree.

What causes large holes in tree trunks?

  • Who done it: Clearwing moths create larger dime-sized craters. These moths also prefer weakened trees. Each species of this moth has their favorite type of tree. But trees like maple, ash dogwood, and cherry often top of the list.

  • What they do: Adult clearwing moths don’t damage trees themselves. Instead, the larvae that emerge from eggs deposited on the bark begin to tunnel, which could disrupt the tissues your tree needs to transport food and water.

  • Other symptoms: Check for a sawdust-like material near the holes or on the ground. Then, look up to see if there are any dead branches.

  • What to do next: Have an arborist confirm that it’s these moths doing the damage. While these don’t do as much harm, the warning signs they leave behind are very similar to boring beetles. Once you know it’s these moths, figure out if you’d like to treat–and how to improve your tree’s health!

What causes rows of holes in tree trunks?

  • Who done it: The yellow-bellied sapsucker, a member of the woodpecker family, is known for its precise tree damage. In search of sugary sap, the bird often opts for maple and apple trees. But they’ll go after lots of other tree species, too!

  • What they do: They feed on sap inside the tree and the insects that are drawn to it, like beetles and ants. Woodpeckers mainly eat the insects (not sap) hiding in your trees.

  • Other symptoms: Sapsuckers peck perfectly neat horizontal (or sometimes vertical) rows in tree bark. Their marks are impossible to miss. If you have an ash tree and the indentations are more sporadic, check your tree for other signs of the emerald ash borer. Woodpecker damage is often an early sign.

  • What to do next: Focus on deterring these birds using the tips below. If your tree is continually targeted, it could be in trouble.

Is there any way to repair sapsucker holes?

Unfortunately, there’s no way to patch up woodpecker damage. You can deter them, though, by wrapping the affected areas in burlap or small gap chicken wire.

That way, pecking birds can’t get to bark. Be sure to remove the covering after the sapsuckers’ migration is over in the spring and again in the fall. Also, these birds are protected under the Migratory Bird Act, so do not attempt to harm, capture or kill these birds.

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