Rose rosette disease - This disease is caused by a new virus, rose rosette virus, that is transmitted by an eriophyid, rose leaf curl mite (Phyllocoptes fructiphilus), which inhabits the shoot tips and leaf petal bases of roses, as well as by grafting but not by seed or many other common vectors. Rose rosette was initially mistaken for a phytoplasma disease; however, heat and tetracycline treatments did not cure the disease showing that a phytoplasma is not the causal agent. Also called witches' broom of roses, it is fatal (average lifespan after infection 22 months) in the shrub Rosa multiflora, commonly found wild or as hedges (and considered a noxious weed in some places). It can also infect other rose species, such as garden rose climbers, miniatures, hybrid teas, floribundas, and antique varieties and is capable of killing these as well. Roses are the only plants known to be susceptible. Symptoms include mosaic pattern on the leaves, malformed leaves and flowers, elongated shoots that are often red, and sometimes thorn proliferation. The distorted growth may be mistaken for herbicide damage. There is no treatment for the disease, and control is limited to controlling the vector and destroying infected plants. It is reported that the causal agent does not survive in the soil, but can survive in root fragments. (From Wikipedia)
Photos from Witches-Broom infestation in the 2014 Dorchester rose garden.