When to treat Cherry tree fungus - Fall or Spring?

Asked October 2, 2013, 12:41 PM EDT

I have two sweet cherry trees in my front yard. They both have a leaf fungus which has caused the leaves to drop prematurely. I have had the trees sprayed to kill the fungus several times this year but this treatment has not worked. I contacted two tree companies one of which said the trees should be treated in October with injections in the trunks rather than a spray. Another company said it would be better to do this treatment in the Spring since the trees will be dormant soon. What is your advice, treat them before winter or after? Both trees are about 8 years old and have gotten this fungus every summer for the past three years but so far have come back strong in the Spring with beautiful flowers and foliage.

Oakland County Michigan

3 Responses

Hello. I am not sure of the fungus, but it is likely cherry leaf spot, which causes cherry leaves to defoliate prematurely during the season. This early defoliation can result in weak trees, and if we have a hard winter, trees may be at risk of winter injury. We will hope for a good winter for your trees.

In terms of treatment, sprays are the way to go and I am wondering which products they are using... the cherry leaf spot fungus has resistance to many of fungicides, which may be the reason the materials are not working. I would find out what they are using, and I can help you determine if the material is effective or not. Also, a fall injection will not NOTHING for leaf spot control next year, so please do not choose this recommendation. Sprays when leaves unfold next spring is the time to begin foliar applications. I can help with a spray program if needed.

Good luck.

Nikki

Thank you for the quick response. We have applied Ortho Max Garden Disease Control spray which says it works on cherry tree leaf spot fungus but as I said it did not work this year. We may have used it too late in the season for it to be effective or maybe we did not apply it often enough (we only applied it twice this summer). It was recommended to us by English Gardens. Is there a more effective fungicide for this problem? When should we apply the first spray next year?

Hmmmmm.... I looked up the active ingredient in Ortho Max, and it is chlorothalonil, which is rated as excellent against the cherry leaf spot fungus. My guess is that you did not spray as many times as warranted. Sweet cherries are less susceptible to CLS than tart cherries, but twice is not too many time for one season. I think the product you are using is good (no resistance concerns), so now you need to get good coverage of the foliage, use the proper rate, and spray prior to rain events. I would begin as soon as the leaves open--closed leaves cannot be infected as the fungus enters the stomates, and stomata are not vulnerable when the leave is still folded. The other thing that might help is our CLS model on Enviroweather (www.enviroweather.msu.edu). You can find the weather station closest to you, and use the model to help guide your spray program. I am not sure where you are located, but choose the weather station closest to you and follow the CLS model to help you time the sprays.http://enviroweather.msu.edu/run.php?stn=msu&mod=f_cls

This model might be helpful to know when to apply the Ortho Max. Let me know if this information is helpful or you need more....

Nikki