Double Knockout Rose odd growth
Hello, my double knockout rose I just planted in July 2019, has large shoots growing from it. I was worried this might be Rose Rosette Virus. They are currently being treated for Black Spot, so you will notice the black spots on the leaves, but the red shoots seem like they are normal growth, but I wasn't certain. Thank you for looking into this.
Macomb County Michigan
From the photos it looks like the odd growth may be coming from the rootstock, i.e. it will produce a different type of rose flower, so if this is the case, you should prune these shoots off as they are competing with the knock out rose. They are also vigorously growing, so this makes me think they are a different rose. Roses are usually grafted, that is, have a rootstock from a rose that is very hardy, so the new plant (your knockout) can live through the winter and the scion (top portion) that contains the growth and flower characteristics of the knock out rose.
It's odd if your roses have black spot as they are known to be resistant for this fungal disease. Have you looked closely to see if your rose may have aphids eating on it? They are small insects but will exude a sticky substance that may cause a sooty mold (black substance) to develop, so this may actually be what is ailing your rose. Here is an extension resource that explains more about knockout roses: https://extension.umd.edu/hgic/topics/rose-rosenot-always-look-%E2%80%98knockout%E2%80%99-landscape-roses