With rose rosette disease now prevalent in the Midwest and spreading through parts of the Plains, there’s a recommended management practice to get a handle on the thorny issue.
Rose rosette disease has been spreading through rose gardens and among wild roses.
While most infections occur from April to June, experts attribute the increase and speed of the disease to hot and dry summers. Roses can also become a victim to the disease when insects known as vector mites blow in on puffs of wind.
Mites can be spread long distances on wind currents.
Rose rosette disease can also spread from contaminated clippers.
Roses are the only plant susceptible to the disease.
Experts say although multiflora is particularly vulnerable, many types of roses are susceptible, especially “Knock Out” roses.
“Knockouts are planted a lot, which is probably the reason why the disease has taken off,” said Raymond Cloyd, a professor and Extension specialist in horticultural entomology at Kansas State University. “It’s a fairly susceptible host to rose rosette disease. Rose rosette disease is fairly prevalent now. It appears to be distributed from Wichita to Topeka, and it’s in eastern Nebraska; in Omaha and Lincoln. Texas has got it too.”
Cloyd told The Fence Post, that all types of roses may be vulnerable, and can develop Rose rosette disease, including climbers, hybrid teas, floribundus, miniatures and “old-fashioned” roses.
“People should still plant roses but plant something other than ‘Knock Out roses,’” Cloyd said.
To add another stickler to an already prickly issue, garden roses that develop the disease, can hold onto Rose rosette disease for years.
“Once the plant has developed symptoms and they’re infected, you might as well get rid of them. You can’t correct the problem,” cautioned Cloyd. “If you see excessive thorniness, or large clusters of roses where the growth is all bunched together, it’s clear there’s a 99 percent chance they’re infected.”
He said the affected mites are found on new young growth on buds, and between stems and leaf areas called petioles.
Other symptoms of plants infected with rose rosette disease include:
■ Rapid stem elongation
■ Thickened stems
■ Multiple stems produced at the end of branches
■ Leaf distortion
■ Leaf reddening
■ Leaf chlorosis with yellow mosaic patterns
■ Abnormal narrow leaflets or smaller than normal leaves
■ Premature lateral bud development
■ Aborted or deformed buds and flowers
■ Sensitivity to frost, contributing to severe dieback
■ Susceptibility to fungal diseases such as powdery mildew
■ Plant death in two to five years
Symptoms appear an average of three months after infection.
“The causative organism is an aster-yellow phytoplasma that affects the phloem tissue,” Cloyd said. “The disease is vectored, or transmitted by the eriophyid mite, as it feeds on infected plants. The mite has four legs compared to eight legs on spider mites and other insects. They’re also three to four times smaller.
Viewing of the mites can be seen with a 10 or 20x hand lens.
Once the proverbial bloom is off the rose, and the rose bush is infected, Cloyd says the best management practice is to completely remove and destroy any and all infected plants.
He also recommends yanking out the roots, and digging out and removing the soil around the root zone.
“It’s important to clear the area of all root material,” Cloyd said.
Next, to reduce the risk of infection to other plants, Cloyd advises lawn gardeners to intensely clean pruners with disinfectant, such as Lysol before using them on the next plant.
Cloyd also suggests eliminating multiflora from the garden.
Lastly, the Horticultural Entomologist recommends using a miticide every two weeks between April and September.
“If you’re just starting to plant roses, just be cognizant of the disease, and if you see symptoms right away ... dispose of the plant,” advised Cloyd. “Think about not planting Knockout roses.”
The best advice: nip it in the bud, so that Knockout roses don’t knock out a beautiful rose garden. ❖
For more information, go to www.ksre.ksu.edu/bookstore/pubs/mf2974.pdf.