The Top Signs of an Infested Tree You Can’t Ignore

Unusual Leaf Damage and Discoloration

One of the earliest and most visible indicators of tree infestation is abnormal leaf appearance. Chewed edges, skeletonized veins, or irregular blotches may signal insect feeding. In pests like Japanese beetles, entire sections of foliage can be eaten away, leaving only delicate vein structures. In other cases, pests like aphids or lace bugs suck sap from leaves, causing a stippled, yellowed appearance that worsens over time. Discoloration may also appear as patchy browning, premature reddening, or early leaf drop. While seasonal changes naturally bring color variation, a healthy tree should not exhibit widespread leaf damage in the middle of the growing season. Comparing the suspect tree to nearby healthy ones of the same species can help confirm if discoloration is abnormal.

Holes and Tunnels in Bark or Wood

Perhaps the most concerning symptom of an infested tree is the presence of small, round or D-shaped exit holes in the bark. These are telltale signs of boring insects, such as the emerald ash borer or Asian longhorned beetle. Beneath the bark, larvae create winding tunnels (galleries) as they feed, cutting off the tree’s ability to transport water and nutrients. If you suspect boring insect activity, look for fresh sawdust-like frass at the base of the tree or lodged in bark crevices. Bark peeling away in irregular patches can also reveal these galleries. Left untreated, severe boring damage can kill even large, otherwise healthy trees within a few seasons.

Excessive Sap Flow or Oozing

Some insect pests, like bark beetles, trigger excessive sap production as the tree attempts to defend itself. This can result in sticky patches, dark stains, or hardened sap beads on the bark. In species like pines, this phenomenon is often called “pitch tubes.” Oozing may also be accompanied by a foul odor if secondary infections set in. Certain pests, such as peach tree borers or weevils, leave behind discolored, frothy, or jelly-like sap exudates. These signs are especially concerning when combined with dieback or leaf loss.

Bark Cracks and Lesions

While cracks in bark can result from natural growth or environmental stress, deep fissures or sunken lesions can be a red flag for pest activity. Some insects introduce pathogens while feeding, leading to cankers—localized dead areas on the bark. Over time, cankers expand, girdling the tree and disrupting its vascular system. Pests such as flatheaded borers may leave elongated scars that differ from weather-related bark splits. If these cracks are accompanied by discolored wood beneath the surface, immediate inspection by a certified arborist is warranted.

Presence of Webs, Nests, or Egg Masses

Many tree pests leave behind visible structures such as webs, tents, or egg clusters. Tent caterpillars and fall webworms create silken nests in branches, often defoliating large sections of the canopy. While these pests may seem harmless at first glance, heavy infestations can weaken trees and make them more susceptible to disease. Egg masses from pests like spotted lanternflies can be found on bark, leaves, and even nearby structures. These masses often resemble mud or putty and can survive harsh winter conditions, hatching in spring to begin a new infestation cycle.

Wilting and Dieback in Isolated Branches

Sudden wilting in individual branches or sections of the crown can indicate localized pest activity. Borers, for example, often attack specific limbs first, cutting off nutrient flow and causing the branch to decline. This type of dieback typically spreads over time, moving from outer canopy sections inward toward the trunk. In conifers, pest damage can result in browning or reddening of specific branch clusters, while the rest of the tree appears healthy. Because early dieback may be subtle, regular inspections from the ground and with binoculars can help catch the problem before it spreads.

Chewed or Girdled Twigs and Branches

Certain pests, like squirrels, voles, and some beetles, chew directly on twigs and bark. This can lead to girdling, where the bark is removed in a complete ring around a stem or trunk. Once girdled, that section of the tree can no longer transport nutrients and will die. Twig girdlers, for instance, cut precise notches in branches to lay eggs, causing the branch tips to drop to the ground. Spotting these cut ends beneath the tree is a clear sign that something is targeting your tree’s smaller limbs.

Unusual Insect Activity on or Around the Tree

Sometimes the easiest way to detect a pest problem is simply by observing unusual insect presence. Large numbers of beetles, wasps, or ants on the bark or around the base of the tree can be an early clue. Carpenter ants, for example, often appear in response to existing wood decay caused by other pests or fungi, signaling a more advanced problem. Flying insect swarms near the canopy or burrowing at the trunk base should never be ignored. Many pests have peak activity periods, so paying attention to seasonal changes in insect activity can help you spot infestations before major damage occurs.

Fungal Growth and Mushrooms

While fungi are not insects, their presence often indicates pest-related injury or stress. Wood-decay fungi, such as conks and shelf mushrooms, thrive in weakened or dying wood. Pest tunneling often creates ideal entry points for these fungi, accelerating the decline of the tree. Mushrooms growing at the base of a tree can signal root decay, sometimes linked to soil-dwelling insect larvae feeding on roots. Once decay sets in, the structural stability of the tree can be compromised, creating a safety hazard.

Unexplained Decline in Tree Health

Sometimes the signs of infestation are more general—gradual canopy thinning, reduced leaf size, stunted growth, or premature fall color. These subtle changes can be easy to miss but may reflect ongoing pest pressure. Over time, the cumulative damage from feeding, boring, and pathogen introduction can tip the balance toward irreversible decline. Routine health assessments, ideally once or twice per year, help catch these changes early. A professional arborist can use specialized tools and knowledge to detect issues that aren’t obvious to the untrained eye.

Acting Fast to Save Your Trees

The key to successful pest management is early detection and prompt intervention. Once a tree is heavily infested, treatment options narrow and removal may be the only solution. By learning to recognize the top warning signs—from leaf damage and exit holes to fungal growth—you can act before the situation becomes critical. Treatments range from targeted insecticide applications and biological controls to pruning and improving tree health through proper watering, mulching, and fertilization. In severe cases, removing and properly disposing of infected material prevents the spread to nearby trees.

Your trees are more than just part of your yard—they’re part of your property’s long-term health and value. Ignoring the signs of infestation puts both at risk. By staying alert, conducting regular inspections, and working with professionals when needed, you can keep your trees strong, vibrant, and pest-free for years to come.