KC Gardens

Roses struggle with a one-two punch: A harsh winter and Rose Rosette disease

Look closely: This plant displays symptoms of Rose Rosette disease. Infected plants must be removed or the contagion will spread.
Look closely: This plant displays symptoms of Rose Rosette disease. Infected plants must be removed or the contagion will spread.

Roses have long been a staple in the landscape. They really surged with the introduction of the ever-popular easy-care varieties, led by Knock Out in 2000. These roses bloom May through November and add a splash of color. But this year many of these plants have lost their dependable edge. Several factors are at play.

First, the combination of temperature swings and drought conditions this winter either killed roses to the ground or damaged the vast majority, leaving weakened plants that are struggling. The plants look stunted and lack their full summer glory.

There are a few things we can do to help these plants recover. Prune out all dead wood. It provides no benefits to the plant and looks bad. A light application of fertilizer helps stimulate new growth.

Though these plants are somewhat drought-tolerant, our hot, dry spring did not aid the recovery. Water roses on a regular basis to promote growth. Extremely stressed plants may need to be replaced.

Another issue is the virus called Rose Rosette, which is widespread and continues to take its toll. Rose Rosette is transmitted by a windblown mite, making control measures ineffective. Once infected, the plant must be removed; failure to do so just spreads the disease more rapidly.

Rose Rosette was introduced into the United States in the 1940s and has slowly evolved. It is now our No. 1 rose-growing problem. Learning to identify this viral disease is the key to reducing its spread.

Rose Rosette can appear in the following ways: rapid stem elongation, leaf distortion, leaf reddening, leaf chlorosis with yellow mosaic patterns, abnormal narrow leaflets or smaller leaves than normal, thickened stems, excessive lateral bud development commonly referred to as witches broom, and excessive thorn production.

If you have a rose cane that grows more robustly than the other canes, is reddish-purple, covered in thorns, develops numerous stems from one spot or has flowers that have not formed properly, you may have Rose Rosette.

Pruning out infected parts of the rose does no good; all pruning does is mask the symptoms. Since this is a viral disease, it is in the sap of the plant. By the time symptoms appear, the sap has spread throughout the entire plant.

The good news is the virus lives only in the sap. Once the bush has been removed, another rose can be planted in the same location since the disease does not live in the soil.

But be alert: Your new rose is at the same risk for becoming infected by the mite.

Examine your roses. Provide good care for those affected by the harsh winter. For those with Rose Rosette, get the shovel out. You will be doing us all a favor.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org.