Black Knot

(Apiosporina morbosa)

Conservation Status
Black Knot
 
  IUCN Red List

not listed

 
  NatureServe

not listed

 
  Minnesota

not listed

 
           
           
           
           
           
           
           
 
Description
 
 

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

 
     
 
Biology
 
 

Season

 
 

Year-round; sporulation in wet weather

 
     
 
Use
 
 

Agricultural pest

 
     
 
Distribution
 
 

Distribution Map

 

Sources

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

 
  5/7/2022      
         
 

Occurrence

 
 

Common and widespread

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

Order

Venturiales  
 

Family

Venturiaceae  
 

Genus

Apiosporina  
       
 

Synonyms

 
 

Botryosphaeria morbosa

Cucurbitaria morbosa

Dibotryon morbosum

Otthia morbosa

Plowrightia morbosa

Sphaeria morbosa

 
       
 

Common Names

 
 

Black Knot

 

 

 

 

 

 

 

 

 
 
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Alfredo Colon

 
    Black Knot   Black Knot  
           
    Black Knot   Black Knot  
           
 
MinnesotaSeasons.com Photos
 
 

On a Twig

 
    Black Knot   Black Knot  
           
    Black Knot      
           
 

On a Trunk

 
    Black Knot   Black Knot  
           
    Black Knot   Black Knot  

 

Camera

     
 
Slideshows
 
Black Knot Disease
Andree Reno Sanborn
  Black Knot Disease  
 
About

Disease of apple and cherry.

 

 

slideshow

       
 
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Other Videos
 
  Combat Black Knot
City of Fort St. John
 
   
 
About

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 www.fortstjohn.ca/black-knot.

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

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 www.clemson.edu/hgic

 
  Black Knot of Plum and Cherry Trees
Integrated Pest Management
 
   
 
About

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
BuckthornMN
 
   
 
About

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

   
  BLACK KNOT FUNGUS!
bushcraftbartons
 
   
 
About

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 http://bushcraftbartons.com/

   
  Black Knot
alcoopextensionvideo
 
   
 
About

Uploaded on Feb 25, 2010

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

   

 

Camcorder

 
 
Visitor Sightings
 
           
 

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  Alfredo Colon
Summer 2019

Location: Maplewood Nature Center

Black Knot  
           
 
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