When people refer to finding “worms” in their trees, they are typically encountering the larval stage of moths or beetles, which are actually caterpillars or grubs. These pests can rapidly defoliate a tree or burrow into its structure, causing stress and potentially leading to decline. Effective management begins with accurate identification, as different larvae require entirely different removal strategies.
Identification of Common Tree Pests
Recognizing the type of larvae present is the first step toward successful removal, since their location and feeding habits determine the necessary action. Common tree-damaging caterpillars can be grouped into categories based on their behavior.
Web builders, such as Eastern Tent Caterpillars and Fall Webworms, are characterized by the noticeable silken nests they create on branches. Tent caterpillars typically build their webs in the crotches of branches in the spring, while fall webworms construct their webs at the ends of branches later in the season. These webs serve as protection, making the larvae inside difficult to reach with surface sprays.
Leaf eaters, or defoliators, like the Gypsy Moth larvae, are often found openly feeding on foliage, causing visible chew marks and thinning of the canopy. These pests are easier to treat because they are exposed on the leaves. The presence of tiny, pellet-like droppings, known as frass, on the ground beneath the tree indicates an active defoliator infestation.
Borers represent the most destructive group, as their larvae burrow directly into the bark and wood. Pests like the Emerald Ash Borer or other wood-boring beetle larvae feed on the cambium and sapwood, disrupting the tree’s ability to transport water and nutrients. Signs of borers include exit holes in the bark, sawdust-like material (frass) pushed out of the tunnels, or a general decline in the tree’s canopy.
Non-Toxic Removal Strategies
For many visible infestations, especially those caught early, initial management can focus on physical and cultural methods that minimize environmental impact. Mechanical removal is the most direct approach for web-building caterpillars. This involves pruning the infested branches, particularly for tent caterpillars and webworms, and immediately disposing of the material to prevent the larvae from crawling back onto the tree.
For smaller, reachable pests, handpicking the larvae off the leaves and dropping them into a bucket of soapy water provides immediate control. A forceful jet of water from a hose can also be used to dislodge sap-sucking insects and smaller larvae from the leaves and branches. These methods are most effective when the pest population is still low.
Applying insecticidal soaps and horticultural oils offers a low-impact chemical control option that works on contact. These substances, often derived from plants or fatty acids, smother or disrupt the pest’s cell membranes upon application. Horticultural oils are generally applied during the dormant season or when temperatures are mild to avoid damaging foliage, while insecticidal soaps require thorough coverage to be effective against soft-bodied larvae.
Selecting the Right Targeted Treatment
When physical removal and low-impact sprays are insufficient, particularly for large trees or serious infestations, targeted treatments are necessary. A biological control option is the bacterium Bacillus thuringiensis (Bt), specifically the kurstaki strain (Btk), which is effective against caterpillars. Btk is a stomach poison that must be ingested by the larvae, causing them to stop eating and die within a few days. It is harmless to humans, pets, and most beneficial insects.
Targeting borers or deeply embedded pests requires using systemic insecticides, which are absorbed by the tree and distributed throughout its tissues via the vascular system. These are applied as a soil drench around the tree’s base or injected directly into the trunk, making the tree toxic to internal feeders like borer larvae. Systemic treatments are preferred for borers because they reach the pest beneath the bark where contact sprays cannot penetrate.
In contrast, contact insecticides, such as pyrethroids, kill pests on the surface. They are sometimes used as a barrier treatment to kill adult borers or newly hatched larvae before they tunnel into the wood. Timing the application to coincide with the pest’s most vulnerable life stage is crucial for both systemic and contact chemical controls. Always follow label directions precisely, as chemical treatments carry a higher risk of non-target harm if improperly applied.
Maintaining Tree Health for Long-Term Prevention
A healthy, vigorous tree is naturally more resistant to pests and can better recover from minor defoliation. Proactive care focuses on reducing tree stress, which often attracts borers and other destructive pests. Ensuring the tree receives adequate water, especially during dry periods, supports its internal defense mechanisms.
Proper fertilization is important, but avoiding excessive nitrogen levels is necessary, as high nitrogen promotes the soft, succulent new growth that many pests find attractive. Mulching correctly by applying a two-to-four-inch layer over the root zone, while keeping it a few inches away from the trunk, helps regulate soil temperature and moisture without creating an environment conducive to pests at the bark level.
Regular inspection of the tree canopy and trunk allows for the early detection of small pest problems before they escalate into severe infestations. Removing dead, diseased, or rubbing branches through proper pruning techniques improves air circulation and eliminates potential entry points for pests and diseases. These consistent maintenance practices reduce the need for reactive pest control measures.