Cedar-Apple Rust on Crabapple Tree - Ask Extension
Good morning, I just discovered some of what I believe to be cedar-apple rust on my beloved crabapple tree. The interwebs have failed me (yet again) i...
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Cedar-Apple Rust on Crabapple Tree #813388
Asked October 06, 2022, 12:16 PM EDT
Good morning, I just discovered some of what I believe to be cedar-apple rust on my beloved crabapple tree. The interwebs have failed me (yet again) in trying to find a solution. Do you have any suggestions on where to turn out what to do? Thank you! Carla from Rochester Hills.
Oakland County Michigan
Expert Response
Good afternoon and thank you for reaching out. Would it be possible for you to attach a photo or two of the entire tree/bush?
Hi. Sorry for the delay I've been away. I hope these are helpful!!!
Cedar Apple Rust: On the leaves, the disease appears on the upper surface as small, faint, yellow spots. Shortly after the appearance of active cedar galls will be found on the alternate host for this fungus, the red cedar. Lesions eventually turn dark yellow to yellow-orange and develop a reddish border. Tiny pustules form in the center of these lesions, eventually turning black. Blisters form on the underside of lesions by midsummer and produce small, tubular projections. As lesions age, they split and the walls curve back, forming a cup with masses of powdery orange to brown spores.
On the fruit, lesions usually appear on the calyx end, similar to those on leaves, but only a bit larger, and are usually slightly raised. A dark-green border forms around the yellow to orange colored lesion as they age. As with all leaf fungal disease, you should rake up and destroy fallen leaves to help reduce the change of the fungal spores overwintering and infecting the tree next year.
The links below will further help you ID cedar apple rust and provide some control options. NOTE: A red cedar must be in the area for cedar apple rust to survive. These two are alternate hosts for the disease.
https://www.canr.msu.edu/news/cedar_apple_rust_a_tale_of_a_fungal_disease_with_two_hosts
https://msuextension.org/pubs/a-guide-to-pests-problems-and-identification-of-ornamental-shrubs-and-trees-in-montana/diseases/cedar-apple-rust.html
Another possibility is a fungal disease called apple scab, which typically causes leaves to fall by late summer. Like most fungal leaf diseases, the apple scab fungus overwinters in infected leaf debris on the ground. In spring, spores are produced on the leaf debris and dispersed by wind and rain and infect new leaves. Infection is most severe under wet conditions. Secondary infections occur throughout the growing season when spores are produced on the newly developed leaf spots which infect adjacent leaves.
Avoid wetting the foliage for prolonged times during the growing season. Prune trees to optimize air circulation. Fruit trees can be treated with fungicides in seven- to ten-day intervals starting from green tip stage until flower petal fall. Products with the active ingredients chlorothalonil, copper, or lime-sulfur are effective in controlling this disease. Strictly follow instructions
on the pesticide labels
Here is some further information:
https://www.washtenaw.org/DocumentCenter/View/16650/Apple-Scab
On the fruit, lesions usually appear on the calyx end, similar to those on leaves, but only a bit larger, and are usually slightly raised. A dark-green border forms around the yellow to orange colored lesion as they age. As with all leaf fungal disease, you should rake up and destroy fallen leaves to help reduce the change of the fungal spores overwintering and infecting the tree next year.
The links below will further help you ID cedar apple rust and provide some control options. NOTE: A red cedar must be in the area for cedar apple rust to survive. These two are alternate hosts for the disease.
https://www.canr.msu.edu/news/cedar_apple_rust_a_tale_of_a_fungal_disease_with_two_hosts
https://msuextension.org/pubs/a-guide-to-pests-problems-and-identification-of-ornamental-shrubs-and-trees-in-montana/diseases/cedar-apple-rust.html
Another possibility is a fungal disease called apple scab, which typically causes leaves to fall by late summer. Like most fungal leaf diseases, the apple scab fungus overwinters in infected leaf debris on the ground. In spring, spores are produced on the leaf debris and dispersed by wind and rain and infect new leaves. Infection is most severe under wet conditions. Secondary infections occur throughout the growing season when spores are produced on the newly developed leaf spots which infect adjacent leaves.
Avoid wetting the foliage for prolonged times during the growing season. Prune trees to optimize air circulation. Fruit trees can be treated with fungicides in seven- to ten-day intervals starting from green tip stage until flower petal fall. Products with the active ingredients chlorothalonil, copper, or lime-sulfur are effective in controlling this disease. Strictly follow instructions
on the pesticide labels
Here is some further information:
https://www.washtenaw.org/DocumentCenter/View/16650/Apple-Scab
