Common Pests Affecting Trees and How to Treat Them
Boring Insects
Of the three insect types, boring insects have the highest potential of causing severe damage or even death to trees. These insects live inside the stems, roots, and branches of a tree and cause damage by tunneling through and feeding on the tissues of the tree. Aside from the damage caused by feeding, these tunnels prevent the tree from circulating water properly, which can starve it of necessary moisture and nutrients.
Borers can be from a wide range of insect species, generally some type of weevil, caterpillar, or beetle. Some typical examples of boring insects are the wood-boring moth caterpillar, bronze birch borer, dogwood borer, elm bark beetle, emerald ash borer, and giant palm weevil. Some species of insect live in trees only during their larval stage.
You can identify the symptoms of a boring insect by checking the tree for the holes left behind in the bark and the presence of insect waste that looks like sawdust at the base of the tree. Ideally you will notice these signs early, before the insects have a chance to cause serious issues. If the damage is severe and the vascular system has been affected, there may be portions of the crown that are wilting and dying. Some trees exhibit cracked bark or dying limbs because of the lack of nutrients.
Prevention
If you know there are specific wood-boring insects common in your area, you can choose tree species that are less susceptible to attack. Regardless of the tree type, you can help prevent infestation by keeping the tree as healthy as possible. Limit pruning to the late fall or winter, as this timing minimizes the chances of insects making their way into the open wound. Likewise, it is important to avoid accidentally damaging the tree when doing lawn care or other activities nearby. Any wound can make the tree vulnerable to boring insects. Also be sure that you remove any fallen branches from your yard as soon as possible, as these insects can easily enter dead and decaying wood.
Treatment
Depending on the type of insect, a systemic or contact insecticide can be used to kill insects and prevent future attacks. You may need to remove part or all of the tree if the infestation is severe.
There are a variety of insects that live in trees, and the majority of them are not harmful. But a few types of insects can cause significant damage, or even death, to your trees if they are left untreated in your yard. In general, tree pests are divided into three categories: chewing insects, sap-sucking insects, and boring insects.
Chewing Insects
Chewing insects feed on the foliage or fruit of trees. Those that only feed on leaves are also called defoliating insects. They can be highly destructive and are especially devastating to fruit crops.
One of the most common defoliating insects is the gypsy moth, which attacks many types of common hardwood trees such as oak, birch, apple, willow, elm, and maple. Other typical chewing insects include bagworms, Japanese beetles, apple maggots, cherry fruit worms, tent caterpillars, and leafminers.
The symptoms of chewing insects are curling or ragged leaves with holes, and brown spots on fruit where the insects have penetrated the protective skin. Some insects consume every part of the leaf except the veins — a process called skeletonization.
Prevention
A healthy, mature tree can usually withstand quite a lot of defoliating insects, and keeping your tree healthy is the best preventative measure against this and all types of pests. A sticky or slippery barrier can interrupt the movement of crawling insects such as caterpillars, preventing them from reaching the leaves.
Treatment
It is best to avoid chemical treatments for tree pests if possible, but jojoba or neem oil are plant-based treatments that kill chewing insects on contact with few side effects. Insecticidal soap also breaks down quickly and is generally considered safe to use.
Sucking Insects
Sucking insects feed on the liquid in leaves, twigs, and stems. Some types remain immobile, and blend in with their surroundings, while others move around continuously to feed on different parts of the plant. Common sucking insects found on trees include scale insects, aphids, leafhoppers, spider mites, and thrips.
To identify the presence of sucking insects, look for the sticky substance (honeydew) they leave behind. Honeydew can also attract sooty mold on leaves. Scale insects, leafhoppers, and aphids are generally large enough to be seen with the naked eye, while spider mites and thrips are tiny and can usually only be identified by other signs of their presence. You might also see spots or streaks on the leaves where insects have fed on them.
Prevention
As with other insect types, a healthy and mature tree is much less likely to fall victim to sucking insects, so try to follow proper watering, pruning, fertilization, etc., to keep your trees in top condition. Horticultural oil works as a preventative during the winter, as it kills hibernating insects in trees during the dormant season.
Treatment
Horticultural oil and insecticidal soap can be effective against a variety of sucking insects. If the infestation is not extensive and is isolated to one part of the tree, you may be able to prune off affected areas.