Last updated: March 28, 2026 | By Carlos Mendez, ISA Certified Arborist
Early detection of tree diseases and pest infestations can mean the difference between saving a valuable tree and losing it entirely. Many tree diseases are treatable if caught early, but once they advance, options become limited and expensive. Here are the most common threats to residential trees and how to identify them.
Fungal Diseases
Oak Wilt: A devastating fungal disease that kills red oaks in as little as 4 to 6 weeks. Symptoms include leaves that wilt and turn brown from the edges inward, rapid leaf drop starting at the top of the canopy, and fungal mats forming under the bark that produce a fruity smell. Oak wilt spreads through root grafts between nearby oaks and by beetles carrying fungal spores to fresh wounds. Prevention includes avoiding pruning oaks during the beetle-active season (April through July in most areas) and severing root connections between infected and healthy oaks.
Dutch Elm Disease: Another fungal disease spread by bark beetles that has killed millions of American elms. Symptoms include yellowing and wilting of leaves on individual branches (called flagging), brown streaking visible in the sapwood when bark is peeled back, and progressive branch death spreading through the canopy over 1 to 3 years. Treatment with fungicide injections can slow the disease if caught early, but there is no cure for advanced infections.
Apple Scab and Other Leaf Spots: Various fungi cause leaf spot diseases that disfigure trees but rarely kill them. Symptoms include dark spots on leaves, premature leaf drop, and reduced vigor over multiple years of infection. Treatment involves fungicide applications in spring when leaves are emerging and improved air circulation through pruning. Raking and disposing of fallen leaves reduces the fungal spore load for the following year.
Insect Pests
Emerald Ash Borer (EAB): This invasive beetle has killed hundreds of millions of ash trees across North America. Signs include D-shaped exit holes in the bark (about 1/8 inch wide), serpentine galleries carved by larvae under the bark, crown dieback starting from the top, increased woodpecker activity (feeding on larvae), and new sprout growth from the trunk as the canopy dies. Preventive insecticide treatments can protect ash trees, but they must be applied before the tree is significantly infested. Treatment costs $100 to $300 per tree annually.
Japanese Beetles: These metallic green beetles skeletonize leaves on a wide range of trees and shrubs during summer. While they rarely kill established trees, repeated heavy defoliation weakens them. Control options include hand-picking beetles (effective for small populations), applying neem oil or insecticidal soap, and treating the lawn with grub control products to reduce the larval population.
Scale Insects: Small, immobile insects that attach to bark and suck sap. Heavy infestations cause leaf yellowing, branch dieback, and a sticky honeydew coating on leaves and surfaces below the tree. Horticultural oil sprays applied during the dormant season are effective against most scale species.
Bacterial Diseases
Fire Blight: A bacterial disease primarily affecting trees in the rose family (apples, pears, crabapples, hawthorns). Symptoms include blackened, shriveled shoot tips that curl into a shepherd crook shape, cankers on branches that ooze during wet weather, and rapid branch death that looks like the tree has been scorched by fire. Treatment involves pruning infected branches 12 inches below visible symptoms using sterilized tools, and applying copper-based bactericides during bloom.
When to Call a Professional
If you notice unusual leaf discoloration, canopy thinning, bark abnormalities, or sudden branch death, consult a certified arborist before attempting treatment. Misdiagnosis can waste money on ineffective treatments or, worse, accelerate the problem. A professional can collect samples, identify the specific pathogen or pest, and recommend targeted treatment.
Protecting your trees from disease and pests starts with vigilant monitoring. Our certified arborists at Landscaper Team provide expert diagnosis and treatment for all common tree diseases and pest infestations. Contact us at the first sign of trouble to give your trees the best chance of recovery.
Frequently Asked Questions
When is the best time to trim or prune trees?
Most deciduous trees are best pruned during late winter or early spring while still dormant, as this promotes vigorous new growth and reduces disease risk. Dead or hazardous branches should be removed immediately regardless of season. Flowering trees should be pruned shortly after blooming to preserve next year flowers. Avoid heavy pruning during late summer and fall when trees are preparing for dormancy.
How do I know if a tree needs to be removed?
Trees should be evaluated for removal when they show signs of significant decay, have large dead branches overhanging structures, display fungal growth at the base, lean dramatically, or have roots damaging foundations and sidewalks. Storm-damaged trees with split trunks or major limb loss may also be unsafe. A certified arborist can assess the tree health and recommend the safest course of action for your property.
Is tree removal covered by homeowner insurance?
Homeowner insurance typically covers tree removal when the tree falls due to a covered event like a storm, lightning, or wind and damages an insured structure. If a healthy tree falls on your lawn without damaging any structures, removal costs are usually the homeowner responsibility. Dead or diseased trees that fall may not be covered if the insurer determines neglected maintenance contributed to the failure.