Knowledgebase
Crab Apple Tree Losing Leaves and Thinning Out #867985
Asked May 11, 2024, 10:53 AM EDT
Oakland County Michigan
Expert Response
The leaves may fall for a number of reasons- wind, normal shedding of excess leaves, leaf spot diseases are some of the most common.
Would you please take 4-5 leaves that fell recently, lay some face up and some face down on a smooth plain sheet of paper( not paper towel, the texture confuses the camera focus), and attach that photo here?
I’m looking for how the leaves are detaching( torn, broken, bitten?), and if the leaves look discolored, distorted in any way?
Thank you for the pictures, Lynn.
This appears to be frogeye leaf spot, which affects leaves, and it is also called black rot when this same fungi affects the fruit.
The time to preventively spray for frogeye leaf spot begins at flower petal fall with one of these fungicides- lime sulfur, captan, mancozeb, myclobutanil or thiophante-methyl. These fungicides should be rotated so that the fungi don’t develop resistance to any one kind.
A tree this large needs a professional certified arborist with the power equipment to properly spray the tree, and the training to safely climb and prune the branches. Have a certified arborist come out and prune out all dead wood, and as much diseased wood as is practical. This will help reduce the overwintering of the fungi in the tree. Find certified arborists by zip code here- http://www.treesaregood.org
There are cultural practices that can manage the occurrence of leaf spots. Here is a guide-
https://blogs.cornell.edu/applevarietydatabase/fact-sheet-frogeye-leaf-spot-black-rot/
I recommend you have MSU Plant and Pest Diagnostic lab confirm that this is frogeye leaf spot since the tree is of high value to you. Please email all your pictures and the question to <personal data hidden>
The email consultation is free. If they need a sample sent in, they will instruct you on how, and what the fee will be.
Later in the season the tree may also show signs of infection with apple scab, another fungi which causes leaves to drop in mid-summer. Again, early spring fungicide sprays are effective in controlling apple scab, and they are the same as you use for frogeye. This bulletin has details-this
https://hort.extension.wisc.edu/articles/applescab/
Follow the guides above for cleanup of leaves and fruit, keeping the tree watered during droughts(no rain expected for 14 days or more). With good care I think the tree may be fine.
