Whether you spell it "wood boring," wood-boring" or "woodboring," the one thing for certain about these insects is that they're a huge problem for trees across Texas. Their tunnels block water and nutrient flow to leaves, while their holes invite plant pathogens to enter a tree. Some wood boring insects actually carry plant diseases on their bodies, so that's a double-whammy.
This article will give you information about the different types of wood boring beetles and insects and ways to prevent infestations from becoming a problem in your landscape.
SIGNS OF WOOD BORING BEETLES AND OTHER BUGS THAT KILL TREES
You may have noticed round or oval shaped holes in the bark of you tree with what appears to be sawdust coming out of the holes. This sawdust is called frass and is none other than the excrement of the cambium-eating tree invaders!
TREE BUGS 101
Although there are many different species of wood boring insects that can cause problems and even kill trees, the steps to prevent their invasion and stop their spread from tree to tree are generally the same.
The term wood boring insect includes a large list of bugs that are most often present as a result of a larger problem with your tree. Most wood boring insects are what scientist call secondary invaders, and attack only after the tree has been weakened by some other stress. Such stress can be caused by environmental factors or an actual tree disease.
Insects are attracted to weakened trees and lay their eggs in the bark. Wood boring beetle larvae hatch from the eggs and begin to feed on the tree, hastening the trees decline.
Some wood boring insects attack perfectly healthy trees and can eventually kill them. These are termed primary invaders.
CONSEQUENCES OF WOOD BORING INSECTS
Unfortunately the problem of wood boring insects—one of many tree health conditions— often goes unnoticed, until plants or plant parts begin to die or show external signs of damage such as dying limbs or leaves. Once the tree’s health reaches a noticeable decline, homeowners begin to see the small and randomly distributed holes in the bark.
These holes are normally round, oval or semicircular and are found in a random pattern on the plant. They may be confused with woodpecker holes. The main difference between woodpecker holes and wood boring insect holes is that woodpecker holes don’t produce frass, and are slightly more ordered than those of the wood-boring insects. For example, the yellow-bellied sapsucker woodpecker produces square holes in rows around a trunk or branch.
Wood-borers dig tunnels in the inner bark layer (cambium), which transports nutrients, and water to the leaves. These tunnels eventually block the cambium and girdle the plant. Eventually everything above and beyond the damage site dies. On occasion, tunneling makes the tree weak, causing limbs and branches to fall. Borer damage can weaken a tree, making it more susceptible to disease as well.
If left untreated, most wood boring insects will cause harm and eventual death to a tree. They cause damage by boring into the stem, roots, or twigs of a tree. Some lay eggs, which then hatch to produce larvae that burrow more deeply into the wood. Most wood-borers are in the immature, or larval, stage of development. They then block off the water-conducting tissue of the tree and become very difficult to manage.
LIFE OF A PEST
Adult borers emerge from infected trees in the spring and summer. After mating, the females fly to a suitable host and lay eggs on the bark, often into the crevices or around the wounds. Hatching occurs about 10 to 2 weeks later. The young larvae quickly tunnel beneath the bark where they feed and grow. Once inside the tree, the borer larvae are no longer vulnerable to insecticide sprays and are seldom detected until serious damage has been done.
TYPES OF BUGS THAT KILL TREES
Wood-boring insects may be broken down into several categories. For more details about particular species of wood-boring insects click here.
1. THE ROUND-HEADED BORER
Round-headed borers or long-horned beetle larvae tunnel underneath bark and into the heartwood of your tree. The larvae of some species are legless but most have three pairs of small legs on the first three segments of the bug. The larvae keep their tunnels packed with frass or they push it out of the holes they produces. You may notice this on the outside of the tree trunk. Many species belong to this group, but most of them are secondary invaders. Keeping your trees healthy will help prevent them from choosing your tree to invade. Some wood-borers in this group include the locust borer, cottonwood border, red-headed ash borer, red oak borer, twig girdler, and twig and branch pruners.
2. THE METALLIC WOOD-BORING BEETLE, AKA THE FLAT-HEADED BORER
The adults of this group have a flat head, are hard-bodied and boat shaped with short antennae. They are actually beautiful until you learn the devastation they can cause. Their bodies have distinctive metallic green, blue, bronze, or copper colors. The larvae are cream-colored and legless with widened, flattened body segments just behind their heads. These larvae tunnel under the bark or into the sapwood to produce oval or flattened tunnels. The tunnels or galleries are often winding and packed with frass. Their tunneling can girdle trunks and branches, killing them. Most of these are secondary invaders and include the bronze birch borer, the flat-headed apple-tree borer and a closely related species that attacks recently transplanted or stressed shade, pecan and fruit trees. The emerald ash borer is a member of this group and currently devastating ash tree populations across the country. For more information about the emerald ash borer click here.
3. THE BARK BEETLE
Bark beetles are a group of wood-borers who tunnel below the bark of trees and/or wood. The adults are small and reddish-brown to black. The larvae are cream colored grubs with no legs. This group includes the European Elm bark beetle that is the carrier of Dutch elm disease. You may be familiar with Dutch elm disease as it was responsible for killing most urban American elm trees. Another member of this group includes the southern pine beetle.
Of all the beetles that kill trees, the southern pine beetle is the number one pest of southern pine in both nature and neighborhoods. The adults are active during warmer months and disperse widely to injured, weakened, or stressed trees in the spring. Although the can attack healthy trees when the beetle populations are high. The larvae tunnel beneath the bark and produce tunnels or galleries that look like the letter “S.” This tunneling girdles the tree, causing eventual death. On pine trees infested with bark beetles “pitch tubes” may be present.
Other bark beetles include Ips engravers, shothole borers, and the Asian ambrosia beetle. The Asian ambrosia beetle attacks healthy or stressed freshly cut elm, pecan, peach, Prunus species, oak, sweetgum and other trees in Texas. Not only do these beetles tunnel in the wood to lay eggs, they also introduce a fungus on which the larvae feed. Visible damage includes wilted leaves on infested branches and protrusions of compressed wood dust from numerous small holes, resembling toothpicks pointing outward.
4. THE WEEVIL
Adult weevils have a mouth where the chewing mouthparts are located. The larvae are legless and cream-colored and general feed in cells or hollowed-out cavities underneath the bark rather than in galleries or tunnels, as do bark beetles. Tree weevils can reduce tree growth and make it more susceptible to other insect infestations.
These insects are the larvae of many different species of moths. They have “false legs” with tiny rows of hooks on the undersides of their bodies. These include carpenterworms, the peachtree borer, ash borer, dogwood borer, southern pine coneworm, and the American plum borer. This particular pest invades improperly pruned branches on many different species of woody ornamentals.
HOW DO I PROTECT MY TREES FROM WOOD BORING INSECTS?
Again, most of these insects are attracted to stressed-out trees. Sick trees actually release unique chemicals that wood-boring insects can smell. The insects fly to their new potential host and in most cases lay eggs on the bark.
Regularly inspecting a tree’s trunk for signs of boring insects to enable early identification and quick treatment is the best way to keep your trees free of pests and disease. It you're unsure, you can always get a Treefix free tree health check.
PREVENTING WITH INSECTICIDE
One prevention method is to keep trees and plants healthy with insecticides, and to do it during times of the year when insects are actually vulnerable to insecticides.
KEEPING TREES HEALTHY
This might sound obvious, but keeping your trees as healthy as possible makes them far less susceptible to tree bugs and tree diseases.
When planting a new tree, be sure to know the trees sun and water requirements. Planting a shade-loving tree such as a flowering dogwood in full sun will eventually invite insects and disease to the struggling tree.
Proper pruning, watering, mulching and fertilization is vital to a thriving landscape. Pruning should be done in the fall or winter to avoid attracting insects to open wounds. Dead or fallen wood should be removed immediately.
Wrapping a tree's trunk to prevent borer attack is NOT effective. It can actually prevent the tree from forming a hard outer bark, thereby making it MORE susceptible to borer damage. However, using plastic trunk protectors to help prevent injury from lawn mowers and weed trimmers is a good idea.
WHAT IF MY TREES ALREADY HAVE WOOD BORING BEETLES OR OTHER INSECTS?
Unfortunately, once trees and shrubs are infested, non chemical options for borer control are limited. One option is to remove and destroy heavily infested or injured plants. Also, inspect damage sites closely to determine if the larvae can be extracted from the plant with a pocket knife, wire or other suitable tool.
A tree health specialist with an applicators license can apply insecticides to prevent the adult wood-borers from laying eggs and entering your tree. Most insecticides are applied as sprays to the trunks and branches, and are non-systemic. That means the insecticide does not move through the trees vascular system, the chemical remains where it is sprayed. While insecticides designed for wood-borers do not kill larvae that have already penetrated the sapwood or heartwood, they will kill adults and larvae tunneling through the treated bark layer.
There are a few insecticides designed to be administered as a trunk-injection. These products are injected into the root flare of the tree and work by delivering insecticides into the cambium and phloem tissues where borers feed.
THINGS TO KEEP IN MIND WHEN USING INSECTICIDES
- Time your treatments to match adult activity. Insecticides are most effective if applied when the adults are emerging and laying eggs. The life cycles of some insect borers are well known in Texas and can be found by contact your local extension service agent or an arborist specializing in tree health care. It is critical to know when adults lay their eggs. For most beetles, the adult egg-laying period is either very long or unknown.
- Surface treatments are effective for only a 3- to 10- week period. Therefore, regular re-treatment of susceptible plant parts is needed for effective control.
- To minimize drift, spray only on days when wind is less than 6 to 7 miles per hour.
OUNCE OF PREVENTION > POUND OF CURE
Keeping your trees and shrubs healthy takes some care, but the payoff is a beautiful and resilient landscape. And spotting wood boring insects early can make all the difference in a tree's life.
Finally, make sure to let your neighbors know if you find any wood boring insects in your trees. If you got 'em, your neighbor probably does, too (and vice-versa). Let's look out for each other, y'all!