Alternaria blotch

Disease

Alternaria blotch

Alternaria mali Roberts

Distribution: An increasing problem in the eastern North America, but has yet to be found north of Virginia.

Photos

Damage can be confused with injury from the fungicide Captan (shown here).

Damage can be confused with injury from the fungicide Captan (shown here). Mid-Atlantic Orchard Monitoring Guide
D

The disease primarily affects the foliage, causing circular, necrotic lesions with a light brown interior (A) that later become surrounded by a darker purplish halo (B). Defoliation can occur by late summer on susceptible varieties that are heavily infected (C). The pathogen can also attack green, woody tissue, but it rarely attacks the fruit.

  • Crops Affected: apples

    Management

    The disease occurs primarily on the variety Delicious. Management requires an integrated approach. Shredding leaf litter in the fall helps to reduce disease pressure the following season (this will also help at reducing apple scab). Controlling red mite populations is essential to achieving control of Alternaria blotch. The strobilurin fungicides are the most effective at controlling Alternaria blotch.

    Similar Species

    This disease can be confused with frog-eye leaf spot and with leaf spotting caused by numerous other pathogens, including cedar apple rust on rust-resistant varieties. Injury from azoxystrobin fungicide (Abound) may also appear similar, but injury from azoxystrobin is most severe on McIntosh, Cortland, Empire, and Gala, whereas Delicious leaves are not affected by azoxystrobin. Similarly, injury from the fungicide captan may produce similar symptoms (D). Alternaria blotch may sometimes be confused with magnesium deficiency. Isolation of the pathogen is usually needed to confirm diagnosis.

About

Resources

Events

Michigan State University
  • Spartans Will.
  • © Michigan State University

MSU is an affirmative-action, equal-opportunity employer, committed to achieving excellence through a diverse workforce and inclusive culture that encourages all people to reach their full potential.

Michigan State University Extension programs and materials are open to all without regard to race, color, national origin, gender, gender identity, religion, age, height, weight, disability, political beliefs, sexual orientation, marital status, family status or veteran status. Issued in furtherance of MSU Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Quentin Tyler, Director, MSU Extension, East Lansing, MI 48824. This information is for educational purposes only. Reference to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned.

The 4-H Name and Emblem have special protections from Congress, protected by code 18 USC 707.

We comply with the Federal Trade Commission 1998 Children’s Online Privacy Protection Act (COPPA).