A gardener wears many hats. And thanks to a Mississippi University plant pathologist, here’s a new one. Dr. Alan Henn describes a rose gardener as “the primary care physician for your roses … since you must understand the cycles of diseases that can wreak havoc upon your garden friends.”
Our hot, humid summers are not ideal for growing roses, especially hybrid teas and floribundas. Actually, we are a breeding ground for some major diseases. Does this discourage gardeners who live in the city whose official flower is the rose? Never. We simply grit our teeth and plant them, fully aware of the extra attention they need to survive. And with care, they do survive and thrive and reward us with magnificent blooms until the first hard freeze.
Roses should already be pruned and putting on new growth — signaling it’s time to start prevention of diseases. So, put on your new “primary care physician” hat and head for the garden.
University of Arkansas plant pathologist Sherri Smith was in Fort Smith recently to lecture on diseases that affect roses and shared the following information:
The most common diseases are black spot, cercospora leaf spot and powdery mildew. If you grow roses, you know the telltale signs. For the uninitiated, here is a brief description:
• Black spot, caused by the fungus Diplocarpon rosea, is easy to identify by black or very dark brown spots with fringed or fuzzy edges on the leaves or on the stems or canes.
• Cercospora leaf spot is similar to black spot but the lesion is circular and smooth with a brown/purplish ring surrounding a gray or tan center. A heavy infestation can defoliate the bush. It is not as common as black spot.
• Powdery mildew has white or gray patches of a powdery fungus on young leaves, shoots, buds and flowers. The white may rub off between your fingers. New leaves may become distorted and dwarfed and turn reddish or purple under the powdery areas. If your bushes had powdery mildew last year, Sherri advises they be sprayed this year. (There is also rose downy mildew that kills roses.)
Fortunately, the same preventive practices can control all three diseases.
Fungicides include Immunox, Bayer Advanced Garden Disease Control for Roses, Bonide, Fertilome Systemic Fungicide or Ortho Rose Pride Disease Control. Check labels for the one best for your garden.
Another disease that plagues Knockout rose gardeners is rose rosette, a virus spread by a tiny eriophyid mite. It is also called witches’ broom. Although hard to spot early, here are some clues: red coloration of new growth, excessive thorniness, elongated shoots and deformed blooms. The bad news is there is no cure. Prompt action is required to keep this wind-blown mite from infecting other flowerbeds. The only alternative is to remove the infected bush(es) and surrounding soil and place in the garbage — not the compost heap.
Unfortunately, there are other diseases that attack roses. And Sherri has detailed information and photos of many of them, including rose canker and anthracnose. Google Arkansas Plant Health Clinic, then go to A-Z search and click on roses. Look for Issue 4, 2017. Since Sherri receives diseased plants from across Arkansas, this site is ideal for learning about and treating diseases in our gardens.
Of course, proper planting and care are key to controlling diseases, Sherri reminds. These include proper plant spacing and pruning to encourage good air circulation, watering in ways to keep leaf surfaces dry as much as possible, good sanitation and using protectant fungicides.
When not diagnosing plant diseases, Sherri is a dedicated rose gardener. And one of her priorities is fragrance: “when I am working in the garden, I want to smell the roses.”
Her advice to rose gardeners: check the labels and select disease-resistant roses.
As a rosarian, she not only grows a variety of roses but knows good companion plants for roses. One of her suggestions is to grow clematis with roses. Other ideal companions are lambs ear, lavender, creeping thyme, sweet William and sweet alyssum.
And when you don your primary care physician persona and head for the rose garden, remember the Hippocratic Oath: “First, do no harm!”
Good news for those of us who are planting butterfly ginger lily for the first time! After the column on the ginger lily appeared, a Crawford County reader reports he has been growing this lily for more than six years. He says it not only survives our winters, it thrives and multiplies each year.
Sunday is Earth Day, and the focus is on ending plastic pollution. You are encouraged to join me in celebrating our Earth by avoiding single use plastics (cups, plates, eating utensils and especially straws) for a day, with a goal of cutting back on their use.
Next week, the topic will be: redworms and roses and other off-the-wall DIYs.
Lucy Fry of Fort Smith is a level 4 Master Gardener and writes the area Master Gardener newsletter. Her column, Gardening for the Record, runs weekly in the Times Record. Send questions to email@example.com.