Leaf-spot disease not likely to permanently harm tree
Q. The magnolia in our backyard doesn’t seem to be thriving. The branches and leaves aren’t as thick and lush as they were a year or so ago. And when I looked closely I realized there are spots on some leaves. What is wrong and what can I do to restore its health and beauty? — R. Bruno, Williamsburg
A. This is one of the leaf spots. There are several fungal leaf-spot pathogens that attack magnolia and their symptoms are somewhat similar. They have similar biology, and thus the management options are more or less the same. The spores of these are wind-blown and splashed about with water, spreading the infection. The cool/wet conditions we have had this spring are ideal for the infection and spread of the pathogen.
The tree has probably had this issue before, perhaps not as severe, and you didn’t notice it. While unsightly and definitely causing a lot of leaf drop, this is not going to kill your tree in the short term. A large tree such as yours, with plenty of reserves and healthy leaf area to continue photosynthesis, should survive bouts of this. But if it continues year-afteryear, it could, coupled with other stresses, weaken and predispose your tree to other pests and diseases.
From the picture, it looks like it has spread top-to-bottom, throughout the tree. There are a few control measures that a homeowner can take to limit the spread, but they are difficult to implement with a tree of this size.
At the onset of symptoms in the spring, copper fungicides can be used to prevent the spread of the infection to other parts of the tree. The timing is important; do it at the first sign of infection. But note, this treatment is preventative, not curative. This should be considered if the tree suffers for several consecutive years.
Selective pruning, to open the tree to sunlight and air circulation, could be beneficial. I would suggest consulting an arborist regarding pruning. Also inquire about possible fungicide applications to control the spread if warranted.
One thing that you can do, which you have probably had some practice with, is to keep the fallen leaves raked. Be sure to remove them from the area and destroy. This will reduce the sources of inoculum and help limit the spread. Also, you can help prevent undue stress to the tree by mulching and ensuring that the tree has the proper water it needs.
The University of Minnesosta Extension article Leaf Spot Diseases of Trees and Shrubs, found at bit.ly/leafspotmanagement, is a good resource with additional tips on control.
And one more thing
Here is a great opportunity for all you backyard vegetable growers to share your weekly abundance of fresh fruits and vegetables with your community. Mike Andruczyk, a Virginia Cooperative Extension horticulture agent, sent me some info on a very worthy cause — the Plant-A-Row in Chesapeake. This is a nationwide program initiated by the Garden Writers Association of America. On Tuesdays, June through September, you can share your garden bounty and canned goods with Chesapeake residents by dropping them off at the Central Library, 9 a.m. to noon. Social-distancing protocols will be followed. For more information, call the Chesapeake Extension Office at 757-382-6348.
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