Miniature Rose Plant Diseases

• Miniature roses are smaller versions of standard roses. Jupiterimages/Photos.com/Getty Images

  True to its name, a miniature rose is a smaller or mini version of the standard-size rose bush. Bred to remain small, these roses produce smaller blooms than tea roses. Grown in containers or used as border plants, mini roses enhance the appearance of an indoor or outdoor spot with their vibrantly colored blooms and beautiful forms. Unfortunately, mini roses are subject to the same diseases as other roses.

Gray Mold

• Caused by the fungus Botrytis cinerea, botrytis blight or gray mold is a common disease that affects ornamental plants including miniature roses. According to the University of Illinois Extension, the damaging disease infects flowers at any stage, and is usually present in early spring during cool and wet weather. However, weak, previously diseased or dying miniature roses are more susceptible to gray mold. Initial symptoms of the disease include tiny water-soaked spots or blisters on the flowers, covered by a fuzzy layer, which immediately deepen in color. Remove wilted or spent flowers to prevent spread, and spray miniature roses with a fungicide specially formulated every spring to treat the disease.

Black Spot Disease

• Perhaps the most damaging disease of roses according to "Rose Diseases and Their Control" by A. R. Chase, the fungal black spot disease defoliates a miniature rose in a single growing season. Caused by the fungus Diplocarpon rosae, symptoms include circular black spots on the foliage surrounded by a yellow halo. Infected leaves turn yellow and fall off the bush. In some cases, cankers or swellings appear on the branches and stems, weakening the entire plant. The fungus spreads through splashing water; those exposed to prolonged periods of irrigation, or on plants watered from overhead. Prune infected areas of the miniature rose plant immediately to prevent the disease from spreading, and discard appropriately so the spores do not have a chance to overwinter in the soil. Treat the bush with preventive sulfur spray in spring, before new growth. Also irrigate the plant at soil level to avoid wetting the foliage.

Crown Gall Disease

• Crown gall is a bacterial disease caused by Agrobacterium tumefaciens that attacks a variety of herbaceous and woody plants. The bacteria responsible for the damaging disease can survive in the soil for up to three years in the absence of a host plant. Symptoms of the disease include large galls or swellings on the canes nearest to the soil. The galls are actually masses of stem tissue that severely damage the plant, even causing it to die in extreme cases. The bacterium penetrates the infected mini rose plant through wounds or cuts caused due to pruning or irrigated water. Once infected, a gardener has no choice but to remove and discard the plant. According to the University of California Extension, purchase hardy, disease-free miniature roses to reduce susceptibility of the plant to crown gall.