Growth on Rose Bush (Rosa acicularis)

Observation: I did not see this on our plants last year but it is all over them this year.

LEO says: These growths may be "galls" developed by the plant as a reaction to insects or mites, among other irritants. This observation has been shared with the UAF Cooperative Extension.

UAF Cooperative Extension Consult: Jessie Moan writes, "It's a little hard to be certain based on the picture, but one likely possibility is that the galls on the leaves are spiny rose galls. These are caused by small wasps and are commonly seen this time of year. The hips should still be fine to harvest. Based on the photo, there's still lots of unaffected leaves on this plant, so I would not suspect it would suffer long-term damage as a result of the galls."

Resources

See more on Prickly Wild Rose (Rosa acicularis) in Wikipedia.

See more on spiny rose galls in BugGuide.