Diagnosing Apple Tree Leaf Spots

Venturia inaequalis

Infected crabapple leaf, midsummer (Esther McGinnis, NDSU)

Symptoms

• Early season – Round, velvety, olive-green spots (less than ½ inch) form on leaves and fruit.
• Midsummer – If infection is severe, leaves will turn yellow and fall prematurely.
• Fruit – Spots turn brown and corky through time; fruit may crack and deform.

Crabapple with thinning crown due to premature defoliation (Aaron Bergdahl, N.D. Forest Service)

Management and other important facts

• When possible, plant resistant cultivars. See “Managing Apple Scab in North Dakota Crabapples” (PP1735).
• Raking and removing fallen leaves helps reduce the source of infection for the following season.
• Prune to allow plenty of air movement, and avoid hitting tree leaves with irrigation water.
• Many fungicides are available to prevent this disease, but the spray schedule is intensive.

Early infection of crabapple fruits (Aaron Bergdahl, N.D. Forest Service)

Authors: Joseph Zeleznik and Kasia Kinzer

Yellow to orange lesions are smooth on top of the leaf (Esther McGinnis, NDSU)

The spore-producing structures are raised on the back of the leaf (Esther McGinnis, NDSU)

Cedar apple rust fruiting bodies on juniper (Terry S. Price, Georgia Forestry Commission, Bugwood.org)

Symptoms

• Disease affects cedars, junipers, apples, and crabapples.
• Yellowish-orange lesions develop on leaves and fruit of infected apple/crabapple trees. Juniper-infecting spores develop in these lesions.
• New infections on junipers result in small galls (or witches'-brooms) that, in moist conditions produce orange gelatinous structures that infect apple/crabapple hosts.

Management and other important facts

• Do not plant the juniper/cedar and apple hosts closely together because both are required for infection.
• Picking the galls or pruning the witches'-brooms off the junipers may mitigate the disease.
• Several species of this pathogen are found in North Dakota. 
• Several apple and crabapple cultivars are resistant to cedar-apple rust.

Authors: Aaron Bergdahl, Joseph Zeleznik

Botryosphaeria obtusa

Frogeye leaf spot with distinctive purple margins (Esther McGinnis, NDSU)

Yellow arrows point to frogeye leaf spot and red arrows point to apple scab (Joseph Zeleznik, NDSU)

Symptoms

• Small brown to tan, nearly circular spots with darker brown margins (frogeye leaf spot) appear on leaves.
• Dark brown, sunken cankers can form on branches and main stems. Leaves on cankered branches turn bright yellow and eventually die. Cankers can girdle and kill branches and stems.
• On fruit, lesions appear as reddish flecks and expand to blotches with a red halo, then, alternating brown and black rings (black rot). Affected fruit can shrivel and remain attached to the tree.

Frogeye leaf spot (Aaron Bergdahl, N.D. Forest Service)

Yellowing leaves indicate a black rot canker (Joseph Zeleznik, NDSU)

Black rot symptoms on fruit (University of Georgia Plant Pathology, Bugwood.org)

Management and other important facts

• Remove and destroy mummified fruit and leaf debris to minimize infection the following year.
• Properly prune out infected branches and dead wood when trees are dormant. See “Basic Guidelines for Pruning Trees and Shrubs” (H1036).
• Fungicides are not recommended.

Authors: Kasia Kinzer and Joseph Zeleznik