8 Common Tree Diseases and How To Treat Them

Healthy trees provide shade, beauty, and environmental benefits, but when trees become diseased, they can quickly turn from assets to liabilities. Trees are susceptible to a range of diseases that can cause serious health problems or even death if left untreated. This guide identifies eight common tree diseases and how to treat them effectively, helping homeowners, landscapers, and gardening enthusiasts protect their outdoor spaces.

Oak Wilt

Oak wilt is a serious fungal disease that affects various oak species, particularly red oaks. It spreads through beetles or interconnected roots. Symptoms include leaves that discolor, wilt, and fall prematurely. If left untreated, the disease can kill an entire tree in just a few weeks.

To treat oak wilt, prune infected branches and sterilize tools between cuts to prevent spreading the fungus. However, applying fungicides to the tree through root injections is the most effective treatment. Prevention is key, so avoid pruning during beetle season as well. If you’re unsure about the risk, consult a professional tree trimming specialist for an evaluation.

Dutch Elm Disease

A fungus causes Dutch elm disease, which can then spread through beetles or root grafting. This disease mainly affects elm trees, leading to yellowing and wilting of leaves, followed by branch dieback. It can kill mature trees’ vascular systems and thus the entire tree within a few months of infection.

To treat Dutch elm disease, remove and dispose of infected branches. Applying systemic fungicides to healthy trees can prevent new infections. Sever root grafts between infected and healthy trees to stop the disease’s spread. Consider planting disease-resistant elm varieties to protect your landscape for years to come.

Fire Blight

Fire blight is a bacterial infection that affects fruit trees, especially apple, pear, and quince trees. The disease causes branches and twigs to appear scorched, with darkened leaves and blackened, sticky cankers on the bark. It’s most common in the spring and spread by insects and rain. Left untreated, it can quickly reduce fruit yields and eventually kill the trees.

To treat fire blight, prune infected branches about 12 inches under the damaged part of the tree during the dormant season. Be sure to disinfect tools between cuts to prevent further spread. Apply copper-based bactericides in the spring to prevent the disease from reoccurring. Remove any fallen debris that might harbor bacterial spores.

Anthracnose

Anthracnose is a fungal disease that affects deciduous trees, including sycamores, maples, and oaks. It causes brown or grayish lesions on leaves, eventually leading to defoliation. In severe cases, it can also cause cankers on branches and stems. This disease thrives in wet, cool conditions, making spring and early summer the peak times for infection.

To treat anthracnose, first remove infected leaves and branches, which will reduce fungal spores. Apply fungicides in early spring before new growth begins. Regular pruning improves air circulation, which reduces humidity and prevents fungal growth. Avoid overhead watering to keep leaves dry and discourage the spread of spores.

Cedar-Apple Rust

Cedar-apple rust is a fungal disease that affects both cedar and apple trees. The disease causes orange, jelly-like growths to appear on cedars and yellowish spots or lesions on apple-tree leaves. If left unchecked, it can weaken trees and reduce fruit production.

To manage cedar-apple rust, remove infected branches from cedars to interrupt the fungal cycle. Apply fungicides to apple trees in early spring, before new growth begins. Prune and promptly dispose of infected parts. Planting apple trees resistant to this disease or creating a distance between cedar and apple trees can also prevent this disease.

Powdery Mildew

Another fungal disease, powdery mildew leaves a white, powder-like coating on leaves, stems, flowers, and fruits. It affects a wide range of trees, particularly those in shaded, moist areas. The disease weakens trees and causes leaves to curl or distort. While it’s rarely fatal, it can make trees more susceptible to other issues.

To treat powdery mildew, apply antifungal sprays or horticultural oils. Prune infected branches during the dormant season to improve air circulation and reduce humidity. Plant trees in well-ventilated areas to prevent future outbreaks. Regularly inspect your trees for early signs, and address the issue promptly to keep it under control.

Root Rot

Root rot is a condition caused by fungi or bacteria that thrive in wet, poorly drained soil. It damages tree roots, causing wilting, yellowing, and stunted growth. Overwatering or planting trees in compacted soil commonly causes root rot. The disease progresses slowly and is difficult to detect until the tree shows symptoms of instability.

To treat root rot, aerate the soil around the tree to improve soil drainage, and reduce how much water you use. If the tree is severely affected, removing it may be necessary to protect surrounding plants. A professional arborist can help you manage soil conditions and prevent the spread of root rot.

Canker Disease

Fungi or bacteria cause canker diseases by infecting a tree’s bark, resulting in sunken, discolored lesions. These cankers may ooze sap, and they can cause tree limbs to die. They typically occur on trees with weakened immune systems or that are under stress. If left untreated, cankers can girdle branches, killing the affected parts.

To treat canker disease, cut away infected areas several inches into healthy wood. Always sterilize tools between cuts to avoid spreading the disease. Apply fungicides during the dormant season to reduce the spread of fungal cankers. If the canker is extensive, consider removing the affected tree to prevent the disease from spreading to others.

Tree Disease Management and Proactive Action

Understanding these eight common tree diseases and how to treat them allows homeowners to maintain healthy landscapes. Regularly inspecting your trees helps you detect early signs of disease before they escalate. Look for symptoms such as discoloration, wilting, or abnormal growth. Taking prompt action, such as pruning or applying treatments, can prevent further damage and keep your trees healthy.

Taking proactive steps can also prevent tree diseases. Pruning dead or infected branches, improving airflow, and using preventative treatments all reduce the risks. If disease symptoms appear, act quickly to manage the issue. When in doubt, consult an arborist for a proper diagnosis and the right course of action.

For trees that require specialized care, an arborist’s expertise can ensure effective treatment. They can evaluate your trees, identify the problem, and recommend the best solutions. Professional care is especially important when you’re dealing with complex diseases. For expert help, contact All Around Arbor for tree health evaluations and treatment plans.