Tree pests are insects and other organisms that feed on leaves, bark, sap, roots, flowers, or fruit, reducing a tree's health and ability to thrive. While many insects are harmless—or even beneficial—others can weaken trees, reduce fruit production, spread disease, or eventually kill trees if infestations become severe. Learning to identify common tree pests early can help protect valuable trees and reduce the need for costly corrective work.

Some of the most common tree pests found in Washington include Emerald Ash Borer, Bronze Birch Borer, Hemlock Woolly Adelgid, Western Tent Caterpillars, Brown Marmorated Stink Bug, Apple Maggot, Codling Moth, and aphids. Each pest affects different tree species and causes different symptoms, ranging from leaf damage and sap loss to branch dieback, bark injury, and declining tree health.

Early signs of tree pest activity include chewed or skeletonized leaves, sticky sap or honeydew, holes in bark, sawdust-like frass, thinning foliage, branch dieback, premature leaf drop, and damaged fruit. Because many insects produce similar symptoms, proper identification is often necessary before deciding whether treatment, monitoring, or no action is appropriate.

Emerald Ash Borer is an invasive wood-boring beetle that attacks ash trees by feeding beneath the bark. The larvae disrupt the tree's ability to move water and nutrients, eventually causing canopy thinning, branch dieback, and death if left unmanaged. Although this pest has devastated millions of ash trees across North America, it remains an emerging concern for the Pacific Northwest, making early detection especially important.

You should contact an arborist if you notice rapid canopy decline, repeated insect activity, extensive leaf loss, holes in the bark, dying branches, excessive sap flow, or signs that valuable trees may be under stress. Early evaluation can often prevent additional damage and help determine whether pruning, monitoring, improved tree care, or removal is the safest course of action.

In many cases, yes. Healthy trees can often recover from minor insect feeding if the problem is identified early and the tree receives proper care. Severe infestations, repeated defoliation, or wood-boring insects can cause lasting damage if left untreated. An ISA Certified Arborist can evaluate the tree's overall condition and recommend the most appropriate management strategy.

Worms found inside apples are often caused by pests such as Apple Maggot or Codling Moth. These insects lay eggs on developing fruit, and the larvae feed inside the apple as it matures. Infested fruit may develop soft spots, tunnels, premature drop, or internal decay. Proper orchard sanitation, monitoring, and integrated pest management are often recommended to reduce future infestations.

Small holes in tree bark may indicate the presence of wood-boring insects such as Emerald Ash Borer, Bronze Birch Borer, or bark beetles. These insects create tunnels beneath the bark where larvae feed on living tissues. However, holes can also be caused by woodpeckers, mechanical injury, or disease, making accurate diagnosis important before treatment decisions are made.

Yes. An ISA Certified Arborist can often identify common tree pests by examining the damage, host tree species, and insect activity. In many cases, clear photographs of leaves, bark, branches, fruit, or the insects themselves are enough for an initial assessment. If needed, an on-site inspection can help determine the extent of the damage and recommend appropriate management options.

You should contact an arborist if you notice rapid canopy decline, repeated insect activity, extensive leaf loss, holes in the bark, dying branches, excessive sap flow, or signs that valuable trees may be under stress. Early evaluation can often prevent additional damage and help determine whether pruning, monitoring, improved tree care, or removal is the safest course of action.