The love affair between gardeners and roses is an enduring yet tricky one. Here in Dallas, our climate and soils are not exactly ideal for most types of roses. When you choose the right variety, find the perfect location, provide a rich, well-draining soil, and dutifully tend to the plant’s nutritional and water needs, you’ll be rewarded with quite a prize. But if placement, soil, and maintenance aren’t just right, you’ll find yourself with bloomless, disease-ridden plants.
So when a new group of low-maintenance landscape shrub roses came along 15 years ago, Dallas embraced them. Knock Out® roses took our landscapes by storm. A few years later, the dwarf Drift® rose series hit the market, and we’ve eagerly planted them en masse as well.
Plants in both of these rose series act more like hardy foundation shrubs than temperamental hybrid tea roses. They require no deadheading and are resistant to most diseases as well as drought. As long as they aren’t planted in shady conditions or very poor soil, there is little you must do to keep Knock Out® or Drift® roses looking beautiful. That is, until rose rosette disease hits them.
Every once in a while, a plant disease comes along that impacts an important plant crop in a big way. Think back to the fungal disease late-blight that wiped out potato plants in the infamous Irish potato famine. Most recently, you may have been aware that planting Impatiens came to a halt due to downy mildew disease. Rose rosette is one of these high-impact diseases—and there isn’t a rose on the market that can hide from it.
Rose rosette disease, also called “witch’s broom,” is a virus spread by a tiny mite. The disease only infects rose plants, but it can infect all varieties of roses. Why have Knock Out® and Drift® roses taken the hardest hit? Simply put, they’re a victim of their own popularity. When you plant a single type of plant en masse, you essentially create a buffet for a disease or pest that feeds on that plant. The disease can spread quickly from plant to plant, causing widespread casualties.
There is currently no cure for the rose rosette virus. Researchers are working on it, but a successful treatment is still a ways off. Systemic miticides available to homeowners are not effective for the mites that spread the disease. While other pesticides and horticultural oils can contact-kill the mites, they are not always effective due to the mite’s small size. Pruning out infected canes from your plant is also not a reliable treatment. Infected canes can take months to show signs, so in that time, the disease continues spreading.
Because the virus can take up to two years to kill your rose plants, it can seem like sprays or pruning techniques are healing them. Soil amendments and fertilizers may also seem to boost the plant for a while. Don’t be deceived. The longer you leave infected rose plants in the ground, the more you’re helping to spread the disease to neighborhood plants and beyond.
Presently, the only responsible option is to remove infected plants immediately, root system and all. Because leftover pieces of root can sprout new infected shoots, it’s best to wait at least a year or two before replanting new roses. Your local nursery and landscape professionals can help you identify the disease if you think your plants may be infected. Best to bring an array of photos to a garden center for identification rather than live infected samples. Or have an experienced landscape professional do an on-site diagnosis. Both can offer up some wonderful blooming alternatives to enjoy in your garden while you wait to replace your rose plants and, more importantly, for a cure.
Leslie Finical Halleck is a Certified Professional Horticulturist with more than 20 years of industry experience. She currently owns and runs Halleck Horticultural, LLC, a green-industry consultancy. Her previous positions include general manager for North Haven Gardens in Dallas and director of horticulture research at The Dallas Arboretum.