Informational table showing disease name, symptoms, pathogen/cause, and management of Crabapple diseases.

Disease

Symptoms

Pathogen/Cause

Management

Botryosphaeria canker

Leaves on affected branches wilt and die. Branches die back and become covered with dark-brown to black, pimple-like fungal fruiting structures. Wood under the bark is dark brown.

Botryosphaeria

Trees most susceptible are those under drought stress. Therefore, irrigate to prevent drought stress. Prune infected branches.

Fire blight

Infected flowers are killed and often remain attached throughout the season. The ends of twigs and branches become brown or black and may curl into a shepherd's crook shape. Dead leaves may remain attached to the tree. Cankers formed the previous season may ooze a cloudy liquid during wet spring weather. Branches will be killed as slightly sunken cankers enlarge into larger branches and even into the main trunk.

Erwinia amylovora

During dormancy when the weather is dry, prune infected branches, cutting at least 4 inches below the base of the canker. Disinfest pruning tools frequently. Fertilize carefully to avoid promoting excessive succulent growth. Remove root suckers and water sprouts while they are small. Grow resistant cultivars (see list below). Remove nearby unwanted plants that are susceptible to fire blight.

Fire blight-resistant crabapples:

Adams, Callaway, David, Dolgo, Harvest Gold, Indian Summer, Jewelberry, Liset, Profusion, Red Baron, Selkirk, and Sentinel.

Scab

Dull, olive-green, velvety fungal growth develops on the surface of leaves and petioles in the spring. Leaves yellow and fall prematurely, giving the tree a thin, bare appearance by mid-season. Infected fruit have circular, rough spots on their surface.

Venturia inaequalis

Grow resistant cultivars (see list below). Rake and destroy fallen leaves and fruit. Apply a fungicide as flower buds begin to show color (early pink) and again 3 weeks later.

Scab-resistant crabapples:

Adams, Baskatong, Brandywine, Callaway, David, Dolgo, Donald Wyman, Malus floribunda, Henry Kohankie, Henningi, Jewelberry, Ormiston Roy, Professor Sprenger, Malus seiboldi var. zum cultivar Calocarpa, Silver Moon, Sugartyme, Malus tschonoski, Weeping Candy Apple, White Angel, and White Cascade have been observed in many locations to have only slight to moderate scab infections.

Cedar-apple cedar-quince, cedar-hawthorn, or Japanese apple rust

Bright-yellow or yellow-orange spots form on leaves. On the upper surface of the leaf spot, small, black fungal fruiting structures form. Later, clusters of cup-shaped structures with fringed edges can be observed on the underside of the infected leaves.

Gymnosporangium juniperi-virginianae (cedar-apple)

G. globosum (cedar-hawthorn)

G. yamadae (Janpanese-apple)

G. clavipes
(cedar-quince)

Remove unwanted junipers growing near crabapples. Do not plant junipers close to crabapples. Remove the galls from juniper branches during dormancy. Where the disease seldom occurs or few leaves are infected, no control is necessary. Where disease is frequent and severe, apply a fungicide first when crabapple flower bud tissue can be seen and at petal fall.

Frogeye leafspot

Small distinct spots with purple margins form soon after the leaves unfold. Old spots become gray with a concentric pattern within them. Leaves yellow and fall prematurely.

Botryosphaeria

Prune dead twigs and branches and remove them from the vicinity of the tree.

Fire blight canker, slightly sunken

Frogeye leaf spot

Apple scab

Apple scab

Botryosphaeria canker and fruiting structures

Cedar rust on the upper leaf surface.

One of the cedar rusts on the lower leaf surface