Viral Diseases of Roses
A virus is a submicroscopic, filterable agent that causes disease, multiplies only in living cells and contains nucleic acid surrounded by a protein coat. Because of their similarity to diseases known to be caused by viruses, many rose diseases have not been conclusively traced to a viral agent. The varied symptoms associated with viral diseases include suppression of chlorophyll production, leaf mottling, yellow ring patterns in leaves, stunting, leaf and flower deformation, witches broom or rosettes and, sometimes, tissue necrosis. Among the transmitting agents of viruses are insects, mites, fungi, nematodes, mechanical means, grafting and seed.
Two of the rose diseases are:
ROSE MOSAIC is identified by chlorotic (yellow) line patterns on the leaves of a rose. These occur in various patterns on leaves which are otherwise a normal green. Symptoms are usually most visible in the spring but, quixotically, the leaves may show no symptom at other times. Infected plants may be less vigorous and reportedly more subject to winterkill but there seems to be no decrease in flower production. Through heat treatments possible only in a laboratory setting, virus free buds can be propagated. Rose mosaic cannot be cured but applications of chelated iron when symptoms appear can produce a temporary cosmetic improvement in the the leaves. To be doubly safe, sterilize shears after pruning an infected rose. Control the disease by purchasing plants certified virus free or remove the bush from the garden.
ROSE ROSETTE has been around forever but its incidence in cultivated roses is increasing in the Midwest. Large public rose gardens as well as home gardens have suffered greatly from its presence so it is remarkable that even the listing of the disease is often omitted from rose disease information. The symptoms of rose rosette include leaflet wrinkling and distortion and witches’ broom (an abnormal, brushlike development of many weak shoots arising at or close to the same point). The most definitive symptoms, though, are new, excessively thorny canes which are an unnatural reddish purple which appear turgid and swollen. Infected canes are much thicker than their parent canes. The disease is caused by the wingless eryophyid mite and is always fatal. Remove and destroy infected plants.