Common Tree Diseases: Identification, Treatment & Prevention Guide

Dutch elm disease, emerald ash borer, oak wilt — canopy losses have been staggering. Your yard trees connect to street trees, parks, forests. Early recognition and holistic, chemical-free management can slow spread. Sometimes removal is the only way to protect the larger canopy.

J'Nell Bryson Landscape Architecture

Emerald Ash Borer (Agrilus planipennis)

What: Green beetle; larvae disrupt water/nutrient transport.
Where: Northeast U.S., spreading south to LA, west to CO.
Hosts: All ash species (Fraxinus spp.).
Signs: Summer yellowing, dead branches. Arborist confirms via bark tunnels.
Treatment: Remove & replace. Replacements: maples (Acer), sycamores (Platanus), hickories (Carya) — hybrid disease-resistant cultivars available.
Prevention: Fungicidal injections exist but not guaranteed.

American sycamore allee, Charlotte, NC. chas architects

Oak Wilt (Ceratocystis fagacearum)

What: Soil-borne fungus spread by beetles & root grafts. Kills in one season.
Where: Midwest & East.
Hosts: Red oak group primarily; also white oak group (incl. southern live oak).
Signs: Growing-season leaves wilt, turn reddish, drop fast.
Treatment: No cure — manage effects, prevent spread.
Prevention: Trenching around oaks breaks root grafts. Follow Oak Wilt Information Partnership pruning guidelines.

Healthy southern live oaks, Austin, TX. Greenwood Homes

Mountain Pine Beetle (Dendroctonus ponderosae)

What: Beetle spreads microbes; epidemic in Rockies.
Where: Western U.S., esp. Rockies.
Hosts: Western pines: Scots, ponderosa, jack, whitebark.
Signs: Red needles — visible only after beetles leave.
Treatment: Early detection critical. Pro pheromone baiting traps beetles locally. Remove infested trees.
Prevention: Water adequately, build healthy soil — drought stress invites infestation.

Mark Beall & Associates

Cotton Root Rot / Texas Root Rot (Phymatotrichopsis omnivora)

What: Soil-borne fungus rots roots.
Where: Southwest U.S.
Hosts: Ash, cottonwood, elm, sycamore, others.
Signs: Sudden wilting → dead leaves/branches. Fungus occurs in pockets — neighbor may have it, you may not.
Treatment: Call arborist at first warm-season wilt.
Prevention: Plant resistant: mesquite (Prosopis), palo verde (Parkinsonia), hackberry (Celtis).

Palo verde allee, Los Angeles. Windsor Companies

Dutch Elm Disease (Ophiostoma spp.)

What: Soil fungi + elm bark beetle vector. Decimated Midwestern street elms.
Where: Primarily Midwest.
Hosts: American elm (Ulmus americana).
Signs: Localized branch wilting (fungus blocks water) → death → beetle spreads.
Treatment: Early detection → aggressive pruning of infected limbs can save tree.
Prevention: Plant disease-resistant hybrid elms.

Mature American elms, arching form. Liquidscapes

Anthracnose (various fungi)

Where: Eastern U.S.
Hosts: Sycamore, ash, oak, privet, dogwood most common.
Signs: Dead leaf spots, distorted growth, defoliation.
Treatment: Early: remove/burn infected foliage. Severe: remove tree.
Prevention: Improve air circulation — anthracnose loves damp.

Kousa dogwood (resistant) & 'Appalachian Blush' flowering dogwood. Harold Leidner Landscape Architects

When in Doubt: Call an ISA-Certified Arborist

Tree doctors evaluate health, diagnose, prescribe. Find one via ISA website, Houzz, or local nursery.

Long-term resilience: Organic, ecologically minded program — healthy soil, judicious water, native/disease-resistant palette.