Ash Disease Management: Anthracnose, Decline, Root Rots, Rust, and Yellows

Comprehensive Ash Disease Management

Ash trees face a diverse disease complex including anthracnose, decline, root rots, rust, and phytoplasma yellows. Effective management requires accurate diagnosis and targeted strategies for each condition.

Anthracnose

Gloeosporium aridum distorts young unfolding leaves with greenish-brown to dark brown spots at tips, margins, and between veins. Fully expanded leaves show light brown/tan blotches. Severe infection causes premature leaf drop. Young twigs girdled/killed. Disease worst on lower branches. Fruiting structures (acervuli) slightly darker than spots; magnification required.

Management: Remove/destroy infected twigs/branches during dormancy. Rake/remove fallen leaves in autumn. Apply fungicide as young leaves/twigs form; continue until weather dry and daily temps average >65°F.

Decline

Slowed growth, tufted branches, progressive branch dieback until much of tree dead. Caused by combination: exposed site, heavy/poorly drained soils, drought, canker fungi, viruses, nematodes, phytoplasmas.

Management: Protect from as many stresses as possible.

Ganoderma Root Rot

Ganoderma lucidum causes branch dieback with root rot; distinctive annual shelf-like fungus on wood (singly/overlapping clusters), brown/reddish-brown top with cream/white margin, up to 14 inches across, varnished appearance.

Management: Fungus appearance is final sign of severe disease. Remove immediately if falling limbs/tree threaten life/property.

Laetiporus Root Rot

Laetiporus sulfureus (formerly Polyporus sulfureus) causes slightly depressed/cracked bark on trees with dying limbs; prone to wind breakage. Massive bright sulfur-yellow/salmon/orange shelf clusters (white with age) form summer/autumn, fall off winter; tiny pores on underside. New shelves form following year. Fruiting occurs long after major damage.

Management: Remove at first infection sign—serious threat to life/property.

Rust

Puccinia sparganioides causes spring yellow-orange leaf spots on white/green ash (East Coast); leaf distortion with orange fruiting structures on leaf undersides/petioles; twig cankers; premature defoliation. Spores blow to Spartina (cordgrass) in salt marshes for overwintering.

Management: Apply spring fungicide to protect young leaves/twigs on typically diseased trees. Don't spray typically disease-free trees.

Yellows (Phytoplasma)

Slowed twig/trunk growth (

Management: Remove infected trees.

Integrated Ash Health Program

Key strategies: anthracnose management through sanitation and timed fungicides; decline mitigation through stress reduction; immediate removal for Ganoderma/Laetiporus (structural failure risk); targeted rust control on susceptible trees; and phytoplasma yellows management through infected tree removal. The combination of biotic and abiotic factors in ash decline requires a holistic approach to tree health care.