black wispy fungus on underside of magnolia branches


North York Toronto tree is about 50 years old flowered beautifully growing well in backyard shaded by Norway maple 20 feet away and honey locust I went to prune some branches and discovered the fungus I have never seen the fungus before in 34 years of carefully monitoring the branches for scale insects. Some of the branches are dead. How do I treat the fungus and handle the branches?


Thank you for contacting Toronto Master Gardeners.

I am sorry to here about the fungus on your Magnolia tree. You did not specify which type of Magnolia you have but when I researched the most common ones here in Toronto they all came up with the same answer.

Magnolias are resistant to most pests. The number one thing Magnolias get is scale as you mentioned. This is the most likely culprit here.

At different times of year the scale will look different. This early in the summer it can just look like a bump on the branch or look like a bud.  As summer progress and it develops through it’s life cycle it becomes much more obvious. It is very difficult to see them until late July. Scale secrets a honey dew that is sticky and sweet. This in turn becomes infected with Black Sooty Mold. This would have the stringy effect you describe. You may also be seeing an increase in flying bugs and ants which the honey dew also attracts. Die back of branches is common with this.

Depending on how much of the tree is affected you may want to cut out affected branches. If a large portion of the tree is affected this may not be an option. Dead branches should definitely be removed. When pruning go back to a main branch to help maintain shape and increase air flow through the canopy. This will help the tree avoid further mold and allow beneficial bugs who feed off scale to get in.

If you decide to go with a pesticide, they must be applied at certain points in the scale’s lifecycle. This would be early spring or late August. You should visit a local nursery to find out what is available and how and when it should be applied. It is important to follow the directions carefully to have the desired effect.

As with any infection it is helpful to clean up any leaves or branches that are on the ground around the tree and you may want to disinfect your cutters before and after pruning.

There could be many reasons why you have this problem now. It is an older tree and you mention shade from near by trees. Is the shade something newer in the Magnolia’s life span? Is it getting as much light as it once did? Is there a change in air flow or amount of water available that may have stressed the tree and made it more susceptible to pests? It is helpful to ensure it has the best conditions possible to recover.

I am including the links below if you would like to read further about this.

Good luck.