Chokecherry Flower Galls

Welcome back to Ask a Naturalist, your own personal Google for information on all things natural on PEI. I’ve been receiving photos of deformed Chokecherry (Prunus virginiana) flowers from around the Maritimes, including this one from Tara Matheson here on PEI. The cause is a fungus, Taphrina confusa. Let’s take a look!

Normal Chokecherry flowers have five white petals and grow in finger-like groups, called ‘racemes’ (inset photo). Once pollinated, each flower will form an edible, deep red fruit with a solid pit in the centre. That pit is the seed from which a new Chokecherry can grow.

However, when Taphrina confusa infects a developing flower, it causes the ovary – the part of the flower that becomes the fruit and seed – to grow abnormally and form a long, greenish-yellow gall. The Chokecherry flower no longer produces fruit or its own seed but instead grows fungal mycelium along with spores that are spread by wind and water. The fungus overwinters as a yeast on twigs and bark. If conditions are right next spring, it will transform into the parasitic phase and infect flowers once again; if not, it will remain an innocuous yeast.

Taphrina confusa doesn’t cause any long-term harm to the tree; the infected Chokecherries will miss a year of fruit and seed production, but that’s just a minor inconvenience for them. The fungus likes cool, wet weather and so it’s not surprising to see the galls popping up around our region this spring!

Taphrina confusa usually infects Chokecherry but it can sometimes be found on Pin Cherry (Prunus pensylvanica) and other Prunus species as well. Like the Black Knot fungus (Apiosporina morbosa) I posted about in April, Taphrina confusa is native and widespread, meaning control at the landscape scape isn’t a viable option. However, if you have particularly valuable trees you want to protect, you can prune off infected flowers, seal them in plastic bags, and place them in your waste bin. (Although, because the fungus may persist as a yeast on twigs and bark, this doesn’t necessarily prevent future infections).

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