Over the past few years, roses have made a comeback in commercial landscapes thanks to the Knock-Out Rose and the Double Knock-Out Rose; they are both resistant to black spot disease and powdery mildew, and are able to produce blooms throughout the growing season, making them favorable for urban environments—until recently.
Landscapers are concerned, because of two environmental factors that are causing health problems to these cultivars of roses. One being rose rosette, a disease that is incurable and spreads very easily—two good reasons why landscapers need to keep an eye out for it.
Once detected, the rose bush should be removed and rid of immediately; doing this will help prevent nearby roses from being infected. However, this can be difficult because symptoms can look similar to ones caused by herbicide damage. It is best to determine damage during the spring when new growth is present.
• Increased growth/rapid elongation of shoots
• Abnormal red discoloration of shoots and foliage
• Witches broom appearance from new growth (prolific clustering of small shoots)
• Overabundance of pliable thorns
• Deformed buds and flowers
• Lack of winter hardiness
• Increased susceptibility to other diseases, such as powdery mildew.
How do you control this disease? The mite, Phyllocoptes fructiphilus, transmits the disease to the roses and by controlling them with an insecticide, the rose’s chances of being infected are lower. Another way to control rose rosette, is by removing multiflora roses that are within 100 yards of the landscape. Multiflora roses are wild and typically grow in weeded areas on roadsides and pastures; they are highly susceptible to rose rosette, and can increase the chances of spreading of rose disease in commercial landscapes.
The other culprit causing health problems in Knock-Out Roses is the Sawfly. Landscapers are seeing an increase in sawfly population, which is likely from the large amount of plantings installed this year. Roses attract sawflies because they make a great incubation spot for their larvae. The best way to control sawflies is to use an insecticide, only when larvae are present.
Chapel Valley highly suggests for their clients to have an integrated pest management program included in their yearly maintenance plan. Our team of certified experts will take preventative actions to control diseases that spread easily. Contact us for more information on our landscaping services.