Problems with Knock-Out Roses

Insect Problems

• Knock Out roses are disease-resistant, but they are not insect-resistant. Aphids, the bane of all roses, also attack the Knock Out roses. They gather on leaves, buds and stems and suck the juices. Spider mites are tiny insects that suck the juices out of the leaves and leave tiny speckles on the leaf surface. Japanese beetles are more common in the eastern states of the U.S., and they skeletonize leaves. Dusts and insecticidal soaps help, and when all else fails a good systemic insecticide works very well.

Disease Problems

• While bred to resist fungal diseases, Knock Out roses are not immune. Diseases typical to roses will also attack the Knock Out series. Black spot is a common rose disease that leaves black spots on the leaves. Gray mold will form a grayish mold on the buds. Powdery mildew shows up as a white powdery substance on the leaves. Rust can show up as reddish spots on the underside of the leaves. Fungicidal soaps or rose systemic fungicide applications can treat all of these fungal diseases.

Environmental Factors

• Certain environmental factors contribute to disease and insect infestations. The roses need to be strong and healthy to resist disease, and for this, they need plenty of light, well-drained soils and low humidity. Some of these factors can't be controlled. Gardeners can do little about the humidity in the, but placing the Knock Out rose in a location where it receives about four hours of sunlight a day may even the odds. Combining adequate sunshine with rich well-drained soils will help the Knock Out roses retain their disease resistance.

Prevention

• Generally, the leaves are the most susceptible parts of a rose, and keeping the leaves dry is the key to the Knock Out rose's disease resistance. Water only the roots of the rose; try not to get water on the leaves. Trim off any disease-infested stems and leaves, and destroy leaf debris. Before pruning or thinning, be sure to sterilize all tools with bleach to prevent spreading disease from one plant to the next.