A couple of weeks ago, I gave a talk to a garden club in Fayetteville. After the talk, a woman came up to me with a piece of a rose in a plastic bag, and asked me what caused the problem. It was rose rosette disease. Unfortunately, this is something gardeners in Central New York are seeing with increasing frequency.
Rose rosette disease is is a viral-like disease carried by microscopic wingless Eriophyte mites. It is spreading unchecked throughout the Midwest, South, and East. This disease first appeared in the US in 1941. The main host of RRD is Rosa multiflora.
Rosa multiflora was introduced from Japan in 1866 both as an ornamental. It was soon used as a rootstock. The US Soil Conservation Service encouraged the planting of Rosa multiflora on farms, stripmined areas and along highways from the 1930s through the early 1960s. This rose can produces a prodigious amount of seeds. Birds eat the seeds and spread them, improving germination by their digestive process. The seeds are viable in the soil for up to twenty years.
Rose rosette disease causes vigorous growth with short intermodal distances (the space between leaves), thick reddish stems and thorns, contorted foliage, and witches brooms. The disease spreads from May through July. It kills roses infected with it within two to five years (depending on the size and health of the rose).
The first thing to do to prevent the spread of RRD is to eradicate any Rosa multiflora on or in the vicinity of your property. Be sure to remove the roots thoroughly and either burn the plants or dispose of them in plastic bags. Encourage your neighbors to do the same.
Reduce stress on existing rose plantings by watering, mulching and fertilizing. Some protection may also be provided by the use of horticultural oils or insecticidal soaps applied weekly throughout the growing season. Remember not to use any foliar sprays on rugosa roses, as that will damage or kill them.
Once a rose is infected there is no cure. Remove any garden rose affected. Be sure to remove all roots as well. Disinfect your pruning shears when moving from one rose to another.
Up to this point, I have not used and do not recommend the use of chemical sprays. There has been some research done on the use of miticides, like Avid, to help control rose rosette disease. If you are considering that approach, follow the directions provided with the miticide carefully. All bushes surrounding an infected bush should be sprayed every five days. To reduce the overall population, spray all your roses every two weeks from the end of April through September.
Rosa setigera, a native species rose is supposedly resistant to rose rosette disease. I have several cultivars with Rosa setigera in their background. I am particularly interested in seeing how they respond. I will be watching my roses carefully for the foreseeable future. You do the same!