How can I stop the leaf drop from rust disease on my flowering crab?
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Answers:
Rust produces reddish/yellow lesions on crabapple leaves but usually does not result in leaf drop. To prevent lesions you can spray a fungicide before symptoms of cedar/apple rust show on your tree. Spray when trees at pink flower bud stage at labeled intervals 1 to 2 weeks past petal fall.
Cedar/Apple rust is a two host disease. Junipers are the alternative host. If you can remove junipers adjacent to your crabs, you may eliminate the disease without chemicals. Also, plant disease resistant crabs. http://www.urbanext.uiuc.edu/treeselecto...
If you are having massive, early leaf drop from your crabapples, you may have something in place of or in addition to cedar/apple rust. Apple scab is another common and serious fungal disease of crabapples that can cause premature leaf drop. Spraying fungicides as leaves emerge and following labeled spray intervals can control apple scab and prevent leaf drop. http://www.urbanext.uiuc.edu/treeselecto...
Here are a couple of web sites from academic agriculture departments that have good information. Hope this helps!
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