*******297********** Rose Problems ()-Hort Answers - University of Illinois Extension
University of Illinois Extension

University of Illinois Extension

Hort Answers

Fungal Disease

Rose Problems

 
Frequency
5 (1 = rare 5 = annual)
 
Hosts
Roses

 
Symptoms

Black spot symptoms include black to brownish spots with wide yellow halos. D

Cankers cause dead areas on the stem that can enlarge and eventually kill the stem or even the entire plant.

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.

Ring spot and mosaic viruses cause yellowish to light green discoloration between the normal green leaf tissue. Rose rosette virus cause tissue to look chlorotic, reddish, stunted, elongated, and/or witches'broom. Rose rosette may have all the symptoms on one plant at the same time.

Crown gall causes light brown to brown galls/growths to occur on roots and stems which may result in the plant's death.

Chlorosis causes yellowing of leaf tissue between the veins. Severe chlorosis causes even the veins to yellow.

Aphids produce honeydew that becomes a sticky substance on the leaves and stem tissue.

Rose midges tunnel into the flower bud preventing the flower from blooming or the flower opens in a distorted and badly injured condition.

 
Life Cycle

In most growing areas, black spot is the most common fungal leaf disease on roses.

Rose leaf diseases (except powdery mildew - needs high humidity) need free standing moisture on the leaves to infect.

Cankers caused by Botrytis, Coniothyrium, Phomopsis or other canker causing organisms attack roses.

Misapplied pesticides can cause injury that can sometimes be confused with virus diseases. Virus diseases include ring spot, mosaic viruses and the rose rosette virus.

Crown gall is an important bacterial disease.

Aphids, rose midge, spittlebug and mites (mites are insect relatives) are some of the more common insects on roses.problems.

Chlorosis is usually due to a high pH but on sandy soils, it is also due to lack of nutrients that result in foliage being yellowish.

 
Management

Fungicides and sanitation are helpful management tools for most foliar rose diseases. Avoid wetting foliage when watering.

To reduce canker problems, 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.

Virus infected plants should be eradicate since there are no chemical controls and insects feeding on virus infected plants are then able to spread the virus to other plants. There are no pesticides that manage virus diseases.

Eradicate crown gall 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.

Carefully wash/hose aphids and spittlebugs off the roses. Insecticides are also available. Rose midge need to be controlled with insecticides and mites with miticides.

Check with your local land grant University Extension Service for suggested pesticides for managing your rose problem.

Check soil pH on clay type soils and for nutrient deficiencies on sandy soils.

 
Related Resources
Home, Yard & Garden Pest Guide
Illinois Commercial Landscape and Turfgrass Pest Management Handbook
U of IL - Distance Diagnosis through Digital Imaging
U of IL - Plant Clinic