Common Tree Diseases

How do trees get diseases?

Most tree diseases need three things together: a susceptible tree, a disease-causing organism and the right conditions, usually moisture and temperature. Stress from drought, flooding, wounding, soil compaction or crowding makes a tree an easier target. Over time, repeated infections and drought can add up, so a tree that looked fine for years may suddenly decline after a hard season. Early attention to stress is cheaper than rescue later.

That is why prevention is mostly about keeping trees growing well. A vigorous tree handles many infections without lasting harm, while a weak one may not.

Weather in a given year changes what you see. A very wet spring often brings more leaf diseases, while a drought season can leave trees open to other problems later. Look at the pattern over several years before drawing a conclusion.

What signs show up on leaves?

Leaf spots, powdery coatings, blotches, curling, wilting, early drop and color changes can all point to disease. Many leaf diseases look bad but do little long-term harm to otherwise healthy trees, especially when they appear late in the season.

Wilting of a whole branch or a sudden collapse in mid-summer is more serious, as it may signal a disease moving through the wood. Note the pattern of damage and which parts of the tree are affected.

Keep records of what you see and when. Many leaf diseases are cosmetic, and an expert can tell you whether yours is the kind that matters. Raking and disposing of fallen leaves from affected trees can reduce some problems, but ask local advice first.

• Spots, blotches or powdery growth
• Wilting that does not respond to watering
• Branches dying back from the tips
• Premature leaf drop

What signs show up on bark and wood?

Cankers, oozing sap, cracked or sunken bark, mushrooms, shelf fungi and soft, crumbly wood are common signs. Decay fungi enter through wounds and slowly weaken the trunk or roots. Dead, dry wood hanging in the crown is a safety concern as well as a health sign, since it can drop without warning.

A tree with extensive decay can look sound and still fail in a storm. Take any large fungus at the base seriously and get an expert opinion.

Can I treat tree diseases myself?

Sometimes, but not often. Many diseases cannot be cured once established, and sprays or injections may help only certain problems at certain times. Wrong products can waste money or harm the tree and the environment.

Never apply a treatment based on a guess. Chemicals must be used according to the label and state rules. Ask an extension office, state forestry agency or licensed professional what, if anything, is appropriate.

• Fungicide and other products only work for specific problems
• Timing and label directions matter a great deal
• Some diseases have no practical cure
• A professional can tell you whether treatment is worth the cost

What can I do to prevent problems?

Good practices go a long way. Plant the right tree in the right place, avoid wounding trunks, prune properly at the right time, keep mulch away from the trunk, and avoid overwatering. Clean tools if you cut diseased wood. Mulch only a thin layer, keep it off the bark, and avoid watering in the evening where leaf diseases are a concern, if your extension office agrees for your species.

Spacing and diversity help too. A crowded planting of a single species can lose many trees at once when a disease finds it.

Choosing species and varieties known to resist common local diseases is one of the most effective steps when you plant. Ask your extension office what does well in your area.

What should I do with diseased wood?

Do not simply stack it and forget. Some diseases and pests survive in cut wood and spread. Ask your state forestry agency or extension office whether there are rules about moving firewood or logs from affected areas. Rules vary by state and county.

If you remove a diseased tree, dispose of wood in ways recommended locally, and avoid moving firewood long distances.

How do I get a diagnosis?

Contact your county extension office or state forestry agency. Many have diagnostic services or can direct you to a plant clinic at a land-grant university. A fee may apply. Many land-grant universities run plant disease clinics for rural residents, and your county office can tell you how to submit a sample properly so that it arrives in good shape.

Take clear photos and, if allowed, collect samples as instructed. Write down when symptoms started, what the weather was like and anything unusual such as construction, flooding or herbicide use nearby.

Last reviewed: November 12, 2026. Written by the Rural Farm Life Editorial Team. See our editorial policy.