wpe5.jpg (2127 bytes)U.P. TREE  IDENTIFICATION  KEY
from Michigan State University Extension

FOREST HEALTH - HARDWOOD LEAF DISEASES

Leaves hold a great amount of nutrients, sugars, and other food resources that attract a wide range of pathogens. Despite the structural and physiological defenses of a leaf, pathogens frequently invade leaf tissues. Symptoms generally include browning, discoloration, curling, and leaf drop. Of course, these are symptoms similar to many insect infestations and nutrient stresses as well. Close examination of an affected leaf (several leaves are better) will usually show a lack of insect presence. Eliminating insects, then a pathogen may be the next likely cause. Wilting and browning leaves often result from a disease of the tree's vascular system, unseen under the bark. Several of the common vascular diseases are mentioned here, but properly belong in the stem and branch disease section. Red text indicates an exotic pest.

Anthracnoses
Dutch Elm Disease
Maple Tar Spot
Oak Wilt
Septoria Canker
Wilts / Verticillium Wilt
 
Anthacnoses (Gloeosporium & Gnomonia spp.): brown spots appear on leaves and can expand to cover the entire leaf, most common in the spring/early summer when weather conditions are cool and moist, more common near watering systems (lawns, golf courses, etc.)     
Hosts: many hardwood species, in the UP-mostly oaks, maples, and balsam poplar
    

 

Dutch Elm Disease (Ceratocystis ulmi): biologically, Dutch elm is a vascular disease that results in browning and leaf loss that might occur throughout a growing season and sometimes multiple growing seasons, it often begins with the yellowing of the leaves on a single branch (called flagging), introduce in 1930     

Hosts: commonly American and slippery (red) elm although all native elms are vulnerable
  

 

Maple Tar Spot (Rhytisma acerinum): not a serious disease but can be locally common, especially during cool-moist summers, circular spots appear dark brown/black

Hosts: all maples
  

 

Oak Wilt (Ceratocystis fagacearum): biologically, oak wilt is another vascular disease that results in browning and leaf loss within a period of several weeks (which is considered quick), introduction unknown but it's been around since at least the 1940s             

Hosts: all oaks but oaks in the red oak group are most susceptible and succumb the quickest

     

 

Septoria Canker (Septoria musiva): brown spots with light-colored centers appear on leaves, leaves can turn brown, outbreaks can occur regionally, favored by wet summers, fungus can move to twigs and allow more harmful pathogen introductions

Hosts: aspens, balsam poplar, certain breeds of hybrid poplar
  

 

Wilts: a number of pathogenic wilts affect various tree species; diagnosis can be difficult in some cases e.g. maple dieback and ash yellows; browning and wilting leaves can be symptomatic of many health issues including diseases, insects, and tree stress; for example, emerald ash borer causes leaf loss due to lack of water flow from disrupted vascular tissue   

Hosts: all tree species
    
[maple dieback, ash yellows]

 

Verticillium Wilt (Verticillium albo-atrum): a soil-borne fungus that moves through a trees vascular system, may affect only a portion of a tree or the entire tree, trees often recover if the infection is small and the tree is otherwise healthy, can occur at any time in growing season,

Hosts: many tree species but especially maples

  
 

 

Image Citations
Dutch Elm Disease (2) - Joseph O'Brien, USDA Forest Service, Bugwood.org
Wilt (1), Maple Dieback - Joseph O'Brien, USDA Forest Service, Bugwood.org
Wilt (2), Ash Yellows - William Jacobi, Colorado State University, Bugwood.org
Verticillium Wilt (1) - William Jacobi, Colorado State University, Bugwood.org
Verticillium Wilt (2) - Joseph O'Brien, USDA Forest Service, Bugwood.org
All others - Bill Cook, Michigan State University Extension


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This site created and maintained by Bill Cook, MSU Extension Forester for the Upper Peninsula of Michigan.   Editing and modification is ongoing.  Submit suggestions, questions, and corrections to cookwi@msu.edu or call 906-786-1575. 

 

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at Michigan Technological University.

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