Diseases of Rosa sp. (Rose)

Rosa sp. (Rose) gets many diseases and "insects." Aphids, rose midge, spittlebug and mites are some of the more common insects (mites are insect relatives) problems. In most growing areas, black spot is the most common fungal leaf disease on roses. Black spot symptoms include black to brownish spots with wide yellow halos. Fungicides and sanitation are helpful.

Other fungal problems are cankers (dead areas on the stem that can enlarge and eventually kill stem or even the entire plant, caused by Coniothyrium or Phomopsis. Avoid stressing plants, prune, water, and fertilize to improve vigor. Prune cankered canes immediately above the second last healthy node below the diseased areas. Fungicides are not very effective.

Rust on roses cause yellow spots that may develop orange pustules. Powdery mildew creates a whitish appearance on leaves (needs several days of cool humid nights and warm days). Mycohaerealla leaf spot causes tan to gray spots with purple to red halos. Botrytis often attacks open blooms on roses. Fungicides and sanitation are helpful.

Misapplied pesticides can cause injury that can sometimes be confused with virus diseases. Virus diseases include ring spot and mosaic viruses. Eradicate infected plants since there are no chemical controls.

Crown gall is an important bacterial disease that causes growths to occur on roots and stems which may result in the plant's death. Eradicate infected plants. Many plants can get crown gall so it is best to leave ground unplanted for years or to grow plants that are highly resistant to this disease.

Check with your local University of Illinois Extension office or garden center for current pesticide recommendations.

Written by James Schuster, Extension Educator, Horticulture, and reviewed by Bruce Paulsrud, Extension Specialist, Plant Pathology and Phil Nixon, Extension Entomologist, University of Illinois at Urbana-Champaign.