Growth on rose bushes

Asked June 26, 2018, 6:21 PM EDT

While removing the dead blooms from our rose bushes, we found quite a number of growths on the stems. Most of them were 1/2 inch to 1 inch in diameter; some were larger and gray in color. What is this growth and is it harmful to the rose bush? Thank you for your advice!

Douglas County Minnesota roses mossy rose gall

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