Black Knot

(Apiosporina morbosa)

Conservation Status
Black Knot
  IUCN Red List

not listed


not listed


not listed


Black Knot is a symptom, not the form, of a parasitic fungus, Apiosporina morbosa, infecting living plants of the Prunus genus.

Knots (galls) are black, irregular, bumpy swellings clasping and sometimes surrounding the twigs and branches, sometimes the trunk, of cherry and plum trees and shrubs. They are elongated, furrowed, cracked, ½ to 12 long, and to 1 in diameter.

Spores are produced during extended rainfalls of six hours or more when the temperature is between 60° and 80°F. They are spread by wind and by rain splashing. Where spores land on current season’s growth or wounded tissue an infection occurs. Growth the first year is very slow. The infection first appears in the late summer as a small, warty, greenish-brown or light brown swelling. The fungus overwinters in this state. The following spring the swelling turns olive green and velvety. Over this growing season (the second year of infection) the knot grows rapidly and has a corky texture. Several knots may merge into a single large knot. Eventually, the knot turns black, hard, and brittle. The Black Knot is usually the first symptom of the disease that is noticed. Tissue toward the center of the knot often dies after two years and is invaded by boring insects. The dead gall tissue is colonized by another fungal parasite, Trichothecium roseum, that gives the knot a whitish or pinkish appearance.

Young infected twigs die the first year of infection. Older branches may last several years. Infections cause the host to lose vigor and may eventually be fatal.


Similar Species

Habitat and Hosts

American plum, black cherry, and other Prunus species




Year-round; sporulation in wet weather


Agricultural pest


Distribution Map



4, 7, 24, 26, 29, 30.




Common and widespread

  Kingdom Fungi (fungi)  
  Subkingdom Dikarya  
  Phylum Ascomycota (sac fungi)  
  Subphylum Pezizomycotina  
  Class Dothideomycetes  









Botryosphaeria morbosa

Cucurbitaria morbosa

Dibotryon morbosum

Otthia morbosa

Plowrightia morbosa

Sphaeria morbosa


Common Names


Black Knot









Visitor Photos

Share your photo of this fungus.

  This button not working for you?
Simply email us at
Attach one or more photos and, if you like, a caption.

Alfredo Colon

    Black Knot   Black Knot  
    Black Knot   Black Knot  

On a Twig

    Black Knot   Black Knot  
    Black Knot      

On a Trunk

    Black Knot   Black Knot  
    Black Knot   Black Knot  



Black Knot Disease
Andree Reno Sanborn
  Black Knot Disease  

Disease of apple and cherry.




Visitor Videos

Share your video of this fungus.

  This button not working for you?
Simply email us at
Attach a video, a YouTube link, or a cloud storage link.


Other Videos
  Combat Black Knot
City of Fort St. John

Oct 1, 2020

Fort St. John, along with many other areas of British Columbia and Alberta, is experiencing a Black Knot fungus infestation. Black Knot, or Apiosporina morbosa, is a deadly tree fungal disease that attacks predominately plum and cherry trees. The fungus can put the tree’s health at risk, and without treatment, can eventually kill the tree.

Learn more at

  Black Knot on Cherries and Plums - James Blake
Clemson University - PSA

Jul 19, 2009

Hi, I'm James Blake, Director of the Clemson Extension Home & Garden Information Center. Today we're looking at a disease known as black knot.

Were along the edge of the Clemson University Experimental Forest looking at a wild black cherry with some strange black growths on the twigs. This disease is known as black knot caused by the fungus Apiosporina morbosa. It infects cherries and plums.

The fungus can infect green shoots but can also enter through wounds. Infection leads to these long, rough galls on the twigs and branches and can even infect the trunks of trees. These galls can range in size from an inch to more than 20 inches. These galls can form on one side of a branch or can encircle the entire branch. When infection circles the entire branch or twig it leads to death beyond the point of the gall.

The duration of the complete cycle of this disease is normally 2 years. After infection occurs in the spring, swellings appear in the fall on the current seasons growth. After being dormant during the winter, the fungus resumes growth in spring and the bark splits revealing olive-green fungal tissue covered with spores. These galls turn darker during the summer and fall and then turn hard and black during the winter. In the following spring, another spore stage is produced on the black knots that starts new infections.

Management of black knot begins with the selection of resistant cultivars. If any galls form on susceptible varieties these galls should be removed 4 inches below the point of the gall. All infected plant material should be destroyed.

For more information on gardening, landscaping, insect and disease problems on your plants, visit the Home & Garden Information Center web site at

  Black Knot of Plum and Cherry Trees
Integrated Pest Management

May 26, 2020

In this video, plant pathologist Ed Zaworski discusses Black knot of plum and cherry trees. Check it out!

  Black knot fungus tutorial

Published on Jan 7, 2013

Buckthorn versus cherry trees - black knot fungus grows on cherry trees but not on buckthorn. Learn to Identify and remove black knot fungus from native cherry trees in your woodland. Get rid of buckthorn - not cherry trees


Published on Mar 27, 2012

NOTE: 4 days after visiting the shelter good weather came by and started to really melt. Visited a forest that was facing South and not North like my shelter. What a difference. I fell upon something I felt I could share.

Showing that this fungus is not Chaga even though they look similar..Please visit our website

  Black Knot

Uploaded on Feb 25, 2010

Dr. Scott Enebak Auburn University School of Forestry & Wildlife Sciences, discusses the characteristics of common forest diseases.




Visitor Sightings

Report a sighting of this fungus.

  This button not working for you?
Simply email us at
Be sure to include a location.
  Alfredo Colon
Summer 2019

Location: Maplewood Nature Center

Black Knot  

Afton State Park

Banning State Park

Bertram Chain of Lakes Regional Park

Big Stone Lake State Park

Big Woods Heritage Forest WMA

Blaine Preserve SNA

Blaine Wetland Sanctuary

Blanket Flower Prairie SNA

Blue Devil Valley SNA

Blue Mounds State Park

Brownsville Bluff SNA

Buffalo River State Park

Bunker Hills Regional Park

Carpenter St. Croix Valley Nature Center

Cedar Mountain SNA

Chamberlain Woods SNA

Charles A. Lindbergh State Park

Chimney Rock SNA

Cleary Lake Regional Park

Clifton E. French Regional Park

Clinton Falls Dwarf Trout Lily SNA

Crow-Hassan Park Reserve

Crystal Spring SNA

Des Moines River SNA

Edward Velishek Memorial WMA

Elm Creek Park Reserve

Englund Ecotone SNA

Falls Creek SNA

Felton Prairie SNA, Bicentennial Unit

Forestville/Mystery Cave State Park

Fort Ridgely State Park

Frenchman’s Bluff SNA

Glacial Lakes Preserve

Glacial Lakes State Park

Glendalough State Park

Great River Bluffs State Park

Hampton Woods WMA

Hastings SNA

Hayes Lake State Park

Helen Allison Savanna SNA

Hyland Lake Park Reserve

Iron Springs Bog SNA

Itasca State Park

John A. Latsch State Park

John Peter Hoffman Spring Brook Valley WMA

Keller Regional Park

Kilen Woods State Park

King’s and Queen’s Bluff SNA

La Salle Lake SNA

Lake Alexander Woods SNA, South Unit

Lake Carlos State Park

Lake Elmo Park Reserve

Lake Louise State Park

Lake Rebecca Park Reserve

Lebanon Hills Regional Park

Leif Mountain

Lester Lake SNA

Lost Valley Prairie SNA

Malmberg Prairie SNA

Mary Schmidt Crawford Woods SNA

Mille Lacs Kathio State Park

Mille Lacs WMA

Minnesota Valley State Recreation Area, Lawrence Unit

Mississippi River County Park

Moose Lake State Park

Mound Prairie SNA

Murphy-Hanrehan Park Reserve

Nerstrand Big Woods State Park

Old Mill State Park

Oronoco Prairie SNA

Oxbow Park & Zollman Zoo

Pigeon River Cliffs

Pin Oak Prairie SNA

Pine Bend Bluffs SNA

Prairie Creek WMA, Koester Prairie Unit

Prairie Creek Woods SNA

Prairie Smoke Dunes SNA

Rice Lake Savanna SNA

Rice Lake State Park

Ripley Esker SNA

Ritter Farm Park

River Terrace Prairie SNA

River Warren Outcrops SNA

Rockville County Park

Rushford Sand Barrens SNA

Sakatah Lake State Park

Savage Fen SNA

Scenic State Park

Schoolcraft State Park

Split Rock Creek State Park

Spring Lake Park Reserve

Spring Lake Regional Park

Springbrook Nature Center

Stanley Eddy Memorial Park Reserve

Sunfish Lake Park

Tamarack Nature Center

Terrace Oaks West

Thompson County Park

Thorson Prairie WMA

Tiedemann WMA

Townsend Woods SNA

Twin Lakes SNA

Uncas Dunes SNA

Upper Sioux Agency State Park

Vermillion Highlands Research Recreation and WMA

Vermillion River WMA

Whitetail Woods Regional Park

Whitewater State Park

Whitney Island SNA

Wild River State Park

William O’Brien State Park

Woodbury WMA

Woodland Trails Regional Park

Zumbro Falls Woods SNA





Last Updated:

About Us | Privacy Policy | Contact Us | © All rights reserved.