Bacterial Diseases of Roses
A bacterium is a unicellular microorganism occurring in a wide variety of forms either as free-living organisms or as parasites, and having a wide range of biochemical, often pathogenic (diseasing causing) properties. The identification of bacteria can be difficult since it involves many procedures. Five genera of true bacteria cause plant diseases but only two are pathogenic to roses. Bacteria enter hosts through wounds and various other means. They are disseminated by people, insects, splashing water or soil or sand. They may remain inactive for years in the soil.
Only Crown Gall will be discussed in this section.
CROWN GALL is caused by a soil-born bacterium for which there are no chemical controls. Rounded light green to light tan growths appear on the roots or bud union of an infected rose. As the growths age, they become darker and more woody. The effect on the rose is failure to grow, very small leaves and few flower buds. At one time, crown gall was a serious problem in nurseries but more stringent sanitation has prevented the disease from infected plants intended for sale. Attempts to cure the disease have employed excision of the gall or treating it with pure chlorine bleach. The fate of the plant seems to depend on the location of the gall which may determine the advance of the disease. Death of the rose will not always result but it will usually decline. If the gardener is determined to keep the plant, a sharp knife or pruning shears may be used to remove diseased material but the blades should be sterilized with 70% alcohol after each cut. If the plant is removed, discard it and replace the soil around the roots with new soil and refrain from planting another rose in that location for several years.