Are You Aware Of A Serious Disease That Is Moving…
Ricky Asked
Are you aware of a serious disease that is moving southward that will kill all Knock Out roses?
The Gardener’s Answer
Hello, Ricky in Kentucky: As far as roses go, the Knock Out roses and other shrub roses are pretty disease-resistant. I am not sure if you are referring to a disease known as Rose Rosette or not, but this is the only serious issue associated with Knock Out roses. It not only affects shrub roses but also multiflora roses. This disease originally thought to be a virus was first detected in the 1930s. It was found out west on wild roses. It is spread by an microscopic, wooly mite as well as grafting. Initial symptoms include abnormal growth that is distinctively red in color with abundant thorns that are usually more rubbery than prickly. It resembles what is known in the plant world as a “witch’s broom.” It usually starts on the new growth of one cane but can quickly spread to the rest of the rose. Unfortunately, miticides are not effective against this insect. If you suspect that your roses are infected you can take a sample to your County Cooperative Extension so the horticulture agent can have it sent off to the University of Kentucky for a proper diagnosis. If you want to read more about this disease, the following link is to the July 2011 issue of the inspector findings in Kentucky: www.uky.edu/Ag/NurseryInspection/newsletter/11news/June2011.pdf
