Leaf Loss - Mid to Late Summer

Asked February 7, 2020, 3:20 PM EST

At our residence in Grosse Pointe Woods, Mi we have a flowering ornamental tree that has dark berries on it. The tree is about 15 high and has beautiful flowers each spring. However, each year by mid summer it begins to suffer leaf loss and by the end of August nearly all leaves have dropped. I'm sorry I don't know the exact tree name but have attached a May 2018 pic of it in full bloom. I do know there are quite a number of similar ornamentals trees in our area and the leaf loss problem appears to be widespread and is quite common. We have been treating it monthly the last two summers with a fungicide at the rate of between 1.5-3# per 1000 sq ft. Granules are applied over the root zone (a similar diameter to the diameter of the branches above) and then watered in. We are using "Infuse" which is described as a systemic fungicide for turf and ornamentals as recommended by a local greenhouse. The active ingredient in the fungicide is Thiophanate-methyl (dimethyl 4,4'-0-phenylenebis(3-thioallophanate)). Unfortunately the treatment has not helped. It would be a shame to lose the tree but by late summer it is no longer beautiful. Do you have any suggestions? Thank you. Jim Giffin

Wayne County Michigan

1 Response

Hello Jim,

Thank you for your picture and your complete history. It makes diagnosis much easier, and more accurate.

You have a beautiful crabapple tree. The little berries are the tiny apples- if you carefully cut some open they will not have a single large hard seed( like a cherry), but should look like an apple.

Apples and crab apples are very susceptible to apple scab, which is a fungus that is particularly bad during wet weather in spring before the leaves have fully developed and matured. Once mature the leaves are less susceptible to the fungus.

There are several cultural things you can do to reduce the problem but, because you probably have a variety of tree that is susceptible, to keep the leaves throughout the season you need to also treat in early spring with a spray fungicide. The amount of sprays you need varies depending on how wet a spring we have. Plan on at least two sprays in a dry spring, and more in long, wet springs.

Here is an article that describes the cultural practices to follow, and the fungicide program

https://extension.umn.edu/plant-diseases/apple-scab#fungicides-1165363

Apple scab fungi, Venturia inaequalis overwinter on plant debris. With suitable temperature and moisture it produces ascospores and releases into the air, typically in early spring. The Thiophanate-methyl fungicide does not control this fungus, from what I read on the product label. Also, I suspect the systemic fungicide takes too long to move into the leaf buds, and infection had already taken place. Once infected a fungicide spray can reduce damage but not prevent it.

If you decide to spray, plant to use at least two different sprays and rotate them, so the fungi in your neighborhood do not build a resistance to the chemical.

The long term alternative is to replace the tree with one of the resistant cultivars now available. This link has access to that list of trees at the bottom of the article-

https://www.canr.msu.edu/news/why_is_my_crabapple_tree_losing_leaves

You may want to hire an arborist to come out, correctly thin the tree, and spray, or teach you how to spray it yourself. To find certified arborists, those professionals who have taken training in care, diseases, pests and passed certification tests, search “Find an Arborist” by zip code here—-

www.treesaregood.org

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