We have a mature ornamental cherry or plum tree that suffered
from brown rot last year. We removed all affected branches and leaves. We were told that we might need to do something else this winter or spring–spray the tree with something, possibly. Can you advise us on how to keep our tree healthy?
I consulted The Organic Gardener’s Handbook of Natural Insect and Disease
Control edited by Barbara Ellis (Rodale Press, 1996), and this resource
recommends doing what you already did, by removing and destroying
affected parts of the tree. At the beginning of the growing season (early
spring) you can spray sulfur to control this fungal disease on blossoms.
If you were growing fruit, you would spray again later in the season to
protect the fruit, but since this is an ornamental tree, it isn’t
necessary. Copper sprays are also used to control the disease. Washington
State University Extension recommends preventive measures, such as
avoiding wounding trees (damaging bark with string
trimmers/weed-whackers/lawnmowers, or making bad pruning cuts). Avoid
wetting the blossoms and leaves, and keep the tree pruned for good air
circulation in the canopy. Avoid excessive nitrogen fertilizer. While the
tree is in bloom, check it frequently for symptoms, and destroy any
diseased parts as soon as you notice them.
I found sources for less toxic (but still not hazard-free) versions of
these fungicides from Peaceful Valley Farm & Garden Supply, but they may
be available at your local garden center as well. Some of these require a
pesticide handler’s license.