Too late to prune crabapple trees and treating rust disease?

Asked April 25, 2018, 12:56 PM EDT

Hello, I have a question of two parts: We have a crabapple type tree , that is perhaps 12 years old, in our front yard. (I believe it is called a "fire" crabapple or "fire" cherry plum, as it produces pink flowers when blossoming, then very small "apples" that the birds eat off). This tree has suffered from a rust like disease (identified by someone at a nursery to whom I brought some leaves) , over the past 3-4 years that does not impact the blossom but causes leaves to begin to fall off in June or so then continue throughout the summer. The leaves are speckled as they fall off, but there are not any insects that I see on them. The tree does not die off as a result, but the leaves do fall, and many many of them, so that by the end of the summer, it appears very thin.
1. Is there anything else I can do to prevent the rust besides using the spray provided to me by the nursery mentioned earlier?
2. Is it too late (this spring) to prune off one rather large branch of this tree? (It is one of about 10 larger branches on this tree which is now perhaps 20 feet tall. I would be particularly concerned if this might make the tree even more susceptible to the rust. Thank you!

Ramsey County Minnesota crabapple trees horticulture

1 Response

It is outside of the recommended time for pruning apple trees. Chances of disease increase with this warmer weather and activity of insects. What you describe is probably apple scab on the leaves. This is quite common. Here is a link to what rust looks like: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/cedar-apple-rust-and-gymnosporangium-ru... There are very definite symptoms. Apple scab is different: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/managing-apple-scab/ Scab can be managed with sanitation and preventative spraying on a set schedule. First spraying needs to be done just as a tip of green appears. Please follow the directions on the label.