Gardening …
K-State horticulture experts explain treatment options
Rose rosette virus and rose black spot disease have been reported in several Kansas counties, causing many rose plants to show signs of stress this spring. (Photo by Meg on Unsplash)
MANHATTAN, Kan. – If you're worried that the roses in your garden seem a little stressed right now, you might not be alone.
Cynthia Domenghini, a horticulture specialist at Kansas State University, said gardeners in several Kansas counties are reporting problems with roses caused by rosette virus and rose black spot disease.
According to Domenghini, typical symptoms of the rosette virus include:
Rapid growth of new shoots. “Witches' broom disease,” or crowding of small branches. Excessive thorns on branches. Small, deformed, reddish-purple leaves. In certain cultivars, reddish-purple stripes or spots appear on the stems and petioles. Plants die.
“Infected plants, including the roots, should be removed and disposed of,” Domenghini said. “Gardening tools that have come into contact with the plants should be disinfected to prevent the spread of the virus.”
Rose black spot is a fungal disease that can cause the following symptoms:
Dark, circular lesions with feathery edges appear on the leaf surfaces. The lower leaves are usually the first to become infected, says Domenghini. Raised, purple spots appear on young branches. Infected leaves turn yellow between the spots. Leaves drop.
“Prevention is the best approach to controlling black spot,” Domenghini said, recommending purchasing resistant rose varieties.
Caring gardeners should also consider watering their roses with drip irrigation to avoid getting water on the leaves, and make sure to plant them in a sunny location with good ventilation.
“When planting, do not crowd the plants,” says Domenghini. “Diseases should be removed from the ground and infected plant parts should be cut off from the plant.”
For gardeners who choose to apply a fungicide, Domenghini suggests treating plants at 10- to 14-day intervals. Recommended fungicides include tebuconazole, myclobutanil, triticonazole and chlorothalonil. “As always, follow label directions carefully,” Domenghini said.
Domenghini and his colleagues in the Kansas State University School of Horticulture and Natural Resources publish a weekly garden newsletter with tips for maintaining home yards and gardens. The newsletter is available online and is also sent to you by email every week.
Those interested can subscribe to the weekly newsletter or submit yard and garden-related questions by emailing Domenghini at cdom@ksu.edu. More information is also available at your local K-State Research and Extension office.
— Pat Melgares, K-State Research and Extension News Service
