Rose Rosette on knockout roses

Asked May 16, 2020, 1:41 PM EDT

I am wondering if I have the rose rosette virus in my knockouts. The past three years I had what I believe to be white flys in early spring, then later followed by Japanese beetles. I was able to adresse these issues, but did a hard prune two years ago. I am wondering if I have had the rosette virus, but it was masked by my hard prune. If not any recommendations to getting these back to their former beauty?

Oakland County Michigan

1 Response

Hello,

It looks like stem canker in your pictures. : “When pruning out cankerous parts of stems, cut back to a strongly growing shoot or branch at least 2 to 3 inches below the infected portion. Before each pruning cut, dip the shears in a disinfectant solution of 70 percent rubbing alcohol, or liquid household bleach (1 part of bleach to 9 parts of water).” This sanitation of the pruners is tedious but is critical to preventing canker.

Using a fungicide early on new growth, watering from below, keeping foliage dry, keeping all debris removed, working in the shrubs only when they are dry will help prevent cankers.. Here is a complete discussion of canker diseases on roses, along with notes on which species are most resistant, good cultural practices to minimize the disease.

https://ipm.illinois.edu/diseases/rpds/626.pdf

Rose rosette disease is characterized by smaller than usual, distorted growth and an abundance of thorny stems. Here are some pictures to compare- https://bygl.osu.edu/node/1113

Here are rose basics, should you need a care reference- http://rocklandcce.org/resources/rose-care

If you aren’t getting good growth, a soil test may be in order. He results will tell you how much fertilizer your soil needs each season for good rose health. See the notice here on how to get a soil test during the Covid shutdown- https://www.canr.msu.edu/spnl/