Planting & Caring for Roses While Avoiding Rose Rosette Disease
By Steve Huddleston
Growing roses in Texas has always had its challenges. Hot weather, poor soils, fungus diseases and insects have either caused homeowners to give up on growing roses or motivated them to overcome these obstacles. Then rose rosette disease (RRD) appeared and took a great toll on roses in general, but especially on Knock Out roses because they had been planted so extensively. In spite of all the challenges, however, roses are irreplaceable and should continue to be used in our landscapes.
Earth-Kind roses are still among some of the easiest roses to grow in Texas. The twenty-one roses that made this prestigious list were planted in native soil with no amendments, were not fertilized, were not sprayed with any pesticides, were not pruned other than to remove dead wood and received no supplemental watering after the first year. These roses fall into categories of dwarf shrubs, small shrubs, medium shrubs, mannerly climbers and vigorous climbers.
Visit http://aggie-horticulture.tamu.edu/earthkindroses/cultivars/ to learn more about these tough roses.
Another group of roses that shows promise in Texas are Kordes roses. These roses have been bred and released from a grower in Germany. For the last fifteen years, this company has not used any pesticides on its breeding stock and has turned out some beautiful, healthy roses. Rosarians are eager to see how well these Kordes roses perform in Texas, but hopes are high based on early trials.
Choose a site that gets 6 to 8 hours of full sun. If you have clay soil, apply a couple inches of expanded shale over the bed site and rototill into the existing clay soil. Expanded shale loosens and aerates the tight, heavy clay. Next, apply a couple inches of aged compost over the bed and rototill it into the expanded shale mix. The result is an organically enriched, aerated raised bed that will provide a wonderful growing medium for your roses.
If you have sandy soil, apply only 3 to 6 inches of aged compost and rototill into the soil. Plant your roses in the bed and then mulch 2 to 3 inches thick with an organic mulch such as shredded hardwood mulch.
February 14 (Valentine’s Day) is the recommended time to prune repeat-flowering roses such as hybrid teas, grandifloras, floribundas, shrub roses and many old garden roses. Roses that bloom only once a year, such as most climbers and species roses, should be pruned after blooming in the spring. These spring bloomers produce flowers on old wood – canes that have hardened over a winter – rather than on new wood. Pruning in February would only remove the spring flowers on these roses. September 1 is the other time to prune roses in order to stimulate good fall bloom. Between spring and fall pruning, remove the spent flowers on your roses to keep them looking tidy. Repeat-blooming roses form their flowers on new growth, so the more they are pruned and stimulated to grow, the more flowers they will produce.
Pruning maintains a reasonable shape and size. Pruning removes dead, diseased or spindly growth and stimulates new growth and flower production. Pruning increases air circulation within the center of the bush and therefore helps reduce fungal problems on the foliage. Remove dead canes and any dead stubs from live canes. Remove any canes with stem canker or fungal diseases by cutting the infected cane below the diseased area. Then clean out any weak, spindly growth and interior clutter. Next, cut off the twiggy ends of each cane, eventually removing at least one-third of every cane. Make all cuts at a 45° angle, about 1/4-inch above a bud eye that faces away from the center of the rose bush. This way, growth will be directed outward, and the center of the bush will remain open for good air circulation.
Rose Rosette Disease (RRD)
A plant virus, called the rose rosette virus, which only affects roses, causes RRD. All roses are susceptible to this virus. The virus is spread by wind-borne eriophyid mites, which tend to hide in buds, on open flowers, at the base of shoots, in leaf axils or under leaf scars. The disease is transmitted when an infected mite feeds on a healthy plant. The mites can crawl from one bush to another if the bushes are touching. The wind can carry the mites over longer distances. Infected mites can also be carried to new rose bushes on gloves, clothing or tools.
A few weeks to months after infection, plants begin to show symptoms of RRD. These symptoms include elongated shoots, red or yellow mottling of leaves, unusual red color of terminal growth, distorted leaves, excessive prickles (thorns), thickened stems, witches’ broom (brush-like cluster of shoots or branches), distorted flowers or flowers that fail to open fully, branch dieback, reduced winter hardiness and increased susceptibility to other diseases. The infected plants soon become eyesores in the landscape.
Once a plant is infected with the virus, there is no cure. Even pruning out the affected parts of the plant will not eliminate the virus. The only solution is to remove the plants – roots and all – and discard. Do not place discarded plants in the compost pile. If you want to replace the diseased roses with more roses, consider waiting one to two months before doing so – just to make sure no shoots come up from any roots left in the soil. If shoots appear, remove them and the roots from which they are growing. When you do replace with more roses, plant them farther apart and interplant them with shrubs, ornamental grasses or tall perennials to keep the mites from crawling from one rose bush to another. Mixed plantings disrupt the disease cycle and slow the spread of the virus.
If you want to learn more about rose rosette disease, go to www.agrilifebookstore.org and search for publication EPLP-010.
In spite of old and new challenges in growing roses, rose lovers still think it’s worth it to grow these shrubs that produce such beautiful and often fragrant flowers. With proper selection and management of your roses, you can grow and enjoy these beloved shrubs in your own landscape for years to come.