03 April 2010

Fungal Alert - Black Knot on Local Schubert Chokecherries

To my dismay, my beloved Bailey's Schubert Chokecherry tree once again has evidence of black knot.  It is unfortunate that I have had to deal with this same fungus the previous two years, but it is now rampant throughout the neighborhood, including the trees planted by the city along the walkways.  Black knot presents itself as a black, crackled mass on a twig or branch.  It is a fungus, and, if left untreated, can girdle the branch or twig causing its demise.  Basically it strangles it.  The only way to treat this, is to remove the afftected limb by cutting about a foot below the diseased area and disposing of it in the garbage.  DO NOT compost it!  It is necessary to cut well below the infected area because the fungus can spread through the tissue beyond what is visible to the eye.  Be sure to use sharp tools, ie. pruners, lopper or saw,  and disinfect with a 10% bleach solution between each cut.

That is my task of the day, to remove and destroy and to contact the city and neighbours regarding their trees. 


JoAnn said...

Anything I can do in the growing season... I have just discovered this fungus?

Shirley said...


Yes, whenever you spot this disease it needs to be addressed immediately to prevent further spreading. It is not too late to remove the affected area. Start by cutting away the affected branch one foot below the knot. Be sure to disinfect your pruners or pruning saw between cuts with a 10% bleach/water solution. Be sure to remove every affected branch.

I did my Schubert chokecherry this spring and there is no further evidence of disease. I'd advise you to carefully inspect your trees (prunus genus) every year, late winter to early spring as it is easier to spot without foliage and is a better time to prune. Prune out affected areas and bag for garbage. That is the best way to curb the disease.

Anonymous said...

I too have just found this horrible disease on my beautiful Shubert Chokecherry. I have read that it is best to remove the infected branches in the winter/fall. Being as I just noticed these large knots now, I don't want to wait. Is it ok to prune the tree in early July? Am I going to damage the tree further by pruning these branches now? Ultimately, is it best to wait until pruning time? Thanks so much-

Shirley said...

At the greenhouse we recommended pruning immediately if black knot is verified. The spores are windborne and can further damage your tree and others. However, I contacted a horticulturist and will let you know what they recommend.

Shirley said...

I've finally heard back from the horticulturist who confirmed that it is best to remove the black knot now. Cut at least 8 inches below visible signs of infection and discard the diseased portion. There is no harm in doing this now versus waiting until the tree is dormant. Waiting allows the disease to spread. Remember to disinfect your tools between cuts with a 10% bleach or alcohol solution.

Anonymous said...

My tree has what looks like black knot. The spot is very close to the trunk. The rest of the branch beyond the spot has no emerging leaves. The trunk adjacent to it looks swollen below the bark for about 5 inches downwards. The swollen part is the same colour as the rest of the trunk. Is this black knot and what do we do?

Shirley said...

Dear Anonymous,

First off, what kind of tree do you have? Is it a Schubert chokecherry or a member of the prunus family? Does the black mass look like the photos? Is it oozing?

Without actually seeing your tree, it is difficult to say for sure if it truly has black knot. How large is the black spot on this branch? Is it on other branches? It is a raised mass?

If you answer yes to the last two questions, I highly recommend you take a sample with the disease to your local nursery along with photos of the tree including the trunk.

The prognosis is fairly good if black knot is caught right away, and it is not in the trunk.

Best wishes and please let me know what you find.


Anonymous said...

Hi again:
The tree is a Prunus virginiana 'Midnight' Shubert Chokecherry. The 3" area on the branch is black - no oozing, not really swollen looking. This is about 4" from the trunk. No other branches are affected. The area of the trunk that joins this branch is swollen in a line that goes up and down the trunk (about 4" each way - it looks like the bark is going to have tiny splits due to the growth underneath. Over the phone, the nursery says that since it is a chokecherry, its probably black knot and its going to die. Should we try to carve out the raised area of the trunk or just enjoy the tree while it still looks good.

Shirley said...

Dear Anonymous,

I'm afraid if the black knot is truly in the trunk, cutting it away will not help the tree. Chances are you would have to remove a fair amount of tissue, leaving the tree vulnerable and susceptible to further problems, including insect damage.

If there are no trees of the prunus genus in the neighbourhood, you could just leave it and enjoy the tree. If branches become brittle, they will have to be removed for safety sake, of course, and eventually you'll have to remove the entire tree. It's difficult to say how long your tree will survive. If the disease girdles the trunk of the tree, death is imminent.

If, however, there are similar trees in the vicinity, to prevent the spread of black knot, I'd remove the tree. If you do it yourself, remember to sterlize your tools once you are done in a 10% bleach solution.

I'm so sorry to hear that it is this bad for your lovely tree.


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