by Carole MacMullan, Fulton County Master Gardener Extension Volunteer
This article is part of Garden Buzz, a series from Appen Media and the North Fulton Master Gardeners, where rotating columnists explore horticulture topics like herbs, insects, and wildlife conservation. Find all Garden Buzz articles here.
When I moved to Atlanta in 2008 and was ready to beginning planting a new garden, I was so excited to find out that a new hybrid rose called the Knock Out rose that bloomed endlessly April through October, was disease resistant and did not need the constant pampering that most roses require. Not only was I captivated by this colorful addition to my garden but so were thousands of other gardeners. In a short amount of time, Knock Out rose became one of the best-selling garden bushes at U.S. garden centers.
Last summer, I observed something very disturbing. Two lush, high-performing rose bushes in the front landscaping at my daughter’s house had a disease. The stems were weird! They had an abundance of thorns, and the flowers were very misshapen and never totally opened. Last fall, hoping to rid the plants of the disease without digging them up, I cut back what appeared to be the diseased portion of the Knock Out rose bush, and I hoped for a miraculous recovery in the spring when new leaves and flowers would reappear. How disappointing to note that when spring arrived, the pruning was not successful. The new growth did not recover, and again the stems had numerous thorns and snarled, distorted flowers.
Now the question was what happened? My research led me to a disappointing conclusion. The roses were dying from a viral disease called Rose Rosette. To attack the rose bush, the virus must have a point of entry. The vector or agent of transmission is the tiny eriophyid mite. These insects have sucking mouthparts allowing the mites to feed on the fluids in the rose bush and give the Rose Rosette virus access to the interior cells and tissues of a rose bush. Once the virus has entered the cells, the DNA is changed and the cells start to produce multiple short thorns along the stem, highly pigmented red leaves and misshapen flowers with petals that are twisted in such a way that they cannot fully open.
Because my fall pruning did not work and there is no cure for this viral infection, as a last resort, I dug up the diseased rose bush including what I hope are its entire root system. I strongly suggest removing the entire root system and soil since they might contain mites. I also suggest not planting another Knock Out rose in the same location once you remove an infected rose.
If you live in a subdivision with a community-wide landscape contractor, the Rose Rosette viral disease will unfortunately begin to affect every Knock Out rose in the entire community. To prevent transmission, take on the task of pruning your own rose bushes in the fall.
CAUTION: All pruning tools need to be sterilized with alcohol or beach to kill any mites and/or viruses on the pruning tools. Many gardeners and landscape contractors do not sterilize their tools after each bush or yard is pruned. As a result, the disease is likely to rapidly spread from rose bush to rose bush. To prevent contamination, I keep a packet of sterile wipes in my wheelbarrow so I can conveniently sterilize my pruning tools as I garden.
I would like to end this column with a tribute to the Knock-Out rose that has adorned many gardens in the U.S. with its beautiful and abundant flowers for the last 24 years. This rose was created by William Radler in 1989 and introduced to gardeners in 2000. Radler produced this cultivar by the meticulous and time-consuming process of crossing several rose cultivars. The new rose was instantly popular and was named an All-American Rose Selection winner in 2000. Since then, more varieties have been created, including the Double Knock Out and Petite Knock Out roses as well as yellow, orange and dark and light pink roses.
Happy gardening!
Learn More
- Mite Vector of Rose Rosette Disease (UGA Extension)
- Rose Rosette Virus – An Emerging Problem (UGA Center for Urban Agriculture)
- Symptoms of Rose Rosette Disease (roserosette.org)
This week’s “Garden Buzz” guest columnist is Carole MacMullan, a master gardener and a Milton resident. She taught biology for 35 years in the Pittsburgh area. In 2012 after moving to Milton, Carole completed the Master Gardener training program and joined the North Fulton Master Gardeners (NFMG) and the Milton Garden Club. Her favorite hobbies are gardening, hiking, biking, and reading.
