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Roses
Roses
Rose Rosette Disease (RRD)
This lethal disease of roses is caused by the rose rosette virus (RRV). Symptoms of the virus are variable and include mosaics, strapped leaves (usually thin), a profusion of shoots with short internodes on one cane (witch’s broom or rosette), hyper-thorniness (profusion of thorns), thickened stems, reddening of foliage and stems, distorted buds and flowers, stem (cane) death, and plant death. The most reliable symptoms for rose rosette identification are excessive thorns and the rosette (witch’s broom).
Some large shrub roses can survive with the disease for many years. However, most plants symptomatic for RRD will decline and die in three to five years. Young plants may die in the first year of symptoms.
The virus is transmitted by the eriophyid mite. These mites are the size of dust particles and are only visible with a microscope (> 40X). Rose rosette disease can also be spread from one location to another by movement of diseased plants. Infected plants may remain without symptoms (asymptomatic) for up to one year, and these plants are very difficult to detect until they are planted and display symptoms of RRD. When plants with symptoms are detected, bag the top of the bush to prevent movement of mites and cut the bagged bush off at the soil line. The root ball can be dug and discarded. Root systems do not have to be bagged as the mites do not live in soil. Pruning symptomatic foliage from an infected plant will not save a plant. When a symptomatic plant is removed, a new plant can be placed in the same location as soon as one week later. Success with the replacement rose is not assured as mites may be blown in from infected roses. Adjacent plants should be watched for several months to make sure they are not infected. If symptoms are detected in a neighboring plant, it should be removed. Prompt removal of infected plants will aid in keeping mite populations low and reduce movement within the garden. If the plant cannot be removed quickly, pruning of rosette(s) will reduce vector populations temporarily since mite populations are fortyfold or greater on rosettes than on asymptomatic tissues. However, removal of rosettes will not “cure” the plant and it will still need to be removed.
Although RRD has killed thousands of roses in the eastern U.S., the disease is manageable. In the rose garden the following steps can reduce the threat of RRD greatly. The first steps are:
1. Know the symptoms associated with RRD (refer to UT Extension publication “SP 806 Early Detection of Rose Rosette Disease”).
2. Remove any bush at first symptoms to prevent mite populations from building on the bush to levels where mites are moving to other bushes.
3. Wait at least one week before planting another bush into the hole left from the plant removal in step 2.
4. Carefully monitor bushes around the location of the plant that was removed. Many gardeners have followed these steps and have successfully managed this disease.
Black Spot: Black spot of rose is one of the most common fungal diseases of roses throughout the world. In a natural environment, this disease is prevalent and becomes a major issue, frequently causing epidemics. It will progressively weaken the plant so that fewer and fewer blooms form if the disease is left unchecked. Plants weakened by this disease are increasingly subject to winter injury.
A temperature of 65°F is ideal for fungal spore germination and the disease develops most rapidly at about 75°F. Temperatures of and above 85°F inhibit the spread of the disease. The fungus survives the winter in fallen leaves and at infection sites on the canes. Spores will not survive in the soil, and individual spores will not survive longer than a month.
As the name implies, infected leaves develop black spots, especially on the upper leaf surface. The circular or irregularly shaped spots can be up to 1/2 inch in diameter and typically have fringed borders. As the disease progresses, the leaf margin begins to yellow, and then the entire leaf. The plant will then start to drop these leaves. The fungus may also infect the canes where lesions appear purple at first then progress to black.
Management: Rake and discard all fallen leaves in the fall. Prune and discard any infected canes. Avoid wetting the foliage, especially during dark cloudy days when it will take longer to dry. Grow plants in an open sunny location to promote rapid drying of the foliage. Do not plant in dense plantings and avoid windbreaks to allow good air circulation. Use resistant varieties for low maintenance plantings. Remove infected leaves during dry weather to help retard the rate of disease spread. Many fungicides are registered for control of black spot . Due to the waxy nature of rose leaves, a spreader should be added to the spray to provide better coverage.
Rose and pear slugs: Sawfly larvae chew the upper surface of rose leaves leaving behind the papery, translucent lower leaf surface and the veins. Heavy defoliation gives plants a brown scorched appearance. Look for sawfly larvae in mid-spring (rose sawflies) and early summer (pear sawflies). Inspect both upper and leaf surfaces to find the small, translucent green larva. Damage from these pests is generally aesthetic and doesn’t usually doesn’t cause serious damage that affects overall plant vigor.
Many insecticides are available for the control of these leaf feeding pests.
Suggested Substitutes
Suggested Substitutes
Keep in mind that it is always a good idea to plant a diversity of material so that a new insect or disease arriving on the scene will not decimate your landscape!!
Instead of planting a plant that is commonly riddled with insect pest and diseases, find one from our list of suggested substitutes from UT Extension Specialists, found here.
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