Thanks for your question.

There are two general causes for misshapen chokecherries:

1). Environmental influences. This has been a rather interesting growing season. The spring was unseasonably early and warm. This was followed by intense and prolonged rain. These factors may have affected the development of the chokecherries.

2). Fungal infection. I think this is the more likely explanation, especially given your observation than you have also seen this situation in wild plum. The infection that I’m considering affects both types of plants. It is called Black Knot Disease. It is especially common during wet conditions, such as we have been experiencing. It is caused by a fungus known as Apiosporina morbosa. The fungus infects the woody parts of the chokecherry, typically its branches and twigs. It enters through wounds or natural openings in the bark. Over time, the infection causes abnormal growths, or galls, to form on the branches. These galls are hard, black, and swollen, and can eventually girdle the branch, leading to dieback beyond the infection site. This is its characteristic feature and is the basis for its name. I would be very interested to know if you see these black swellings any place on the chokecherry bush. Give things a thorough inspection. Don’t just look on branches where there are berries. As this fungus grows, it affects the normal development of berries, causing them to become misshapen and swollen. Ultimately the berries become blackened and disfigured. The bright spot is that usually this is not a fatal condition for the bush unless things get very severe. See the following for further information as well as remedial procedures:

https://extension.umn.edu/plant-diseases/black-knot

https://hort.extension.wisc.edu/articles/black-knot-apiosporina-morbosa/

https://byf.unl.edu/black-knot

https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/black-knot/

In short, inspect the bush for these swellings. Keep in mind, however, that in the initial stages of this infection (i.e., within the first or second year), the swellings may be very small and inconspicuous. After you have looked things over, please get back to us with your findings.

Good luck. Thanks for consulting us.

If last year (2023) was the first time you noticed the abnormal berries, and if things are better this year (2024), this would suggest that the infection is still in a very early stage.  These galls typically develop after the infection has been going on for several years.

Thanks again for consulting us.  Good luck for 2025