The Problems of Rugosa Roses

Choosing disease-resistant cultivars helps avoid many rugosa rose problems.

The rugosa rose is a beautiful, but resilient, shrub rose. The large blossoms fill the garden with color, while the crinkled foliage adds texture to the landscape, even when the shrub is not in bloom. The extreme vigor of the rugosa rose makes it a common choice for difficult areas, such as seaside gardens and hot, dry climates. However, the fragrant flowers draw insects, such as aphids, Japanese beetles and borers, and the growing conditions can lead to the development of diseases, such as black spot and powdery mildew.

Diseases

While many rugosa rose cultivars are disease resistant, fungal infections are still fairly commonplace. If allowed to run rampant, fungus can disfigure leaves and weaken plants, defoliating those that are most susceptible. Black circles surrounded by yellow rings characterize black spot, a fungal infection that affects many types of roses. Black spot is most common in hot, humid areas and on foliage that stays wet for hours. Leaves that look as though they have been coated in white powder may be infected with powdery mildew, another common fungal infection. Powdery mildew flourishes in damp conditions and cramped, crowded gardens, where air circulation is poor.

Fungicide

Many fungal spores overwinter on infested foliage. Seasonal cleanup goes a long way toward preventing the spread of diseases; however, should an infection persist, the application of a fungicidal spray may be necessary. Treat the affected foliage with a solution made from 1 tbsp. of baking soda and 1 gallon of water to discourage fungal growth. Add a few drops of dish soap to the solution, if desired, as it will help the liquid stick to the leaves. Spray infected roses every four days until the fungus is no longer apparent. Apply the solution in the morning, so the leaves can dry quickly; lingering wetness encourages fungal growth.

Pests

Nothing is more disturbing than spending the summer watching a favored rose bush succumb to insect damage, leaf by chewed-up leaf. Small as they are, insect pests can cause permanent damage to rugosa roses. The insignificant-looking aphid can colonize a small shrub in a matter of weeks, covering every green leaf with minuscule pests that will literally suck the life out of the plant. Metallic, blue-green, Japanese beetles eat holes in rugosa roses, skeletonizing leaves and flowers in the process. Borer beetles lay their eggs on the branches of the rose bush; their larvae burrow into the stems and live off the internal fluids of the plant until they reach adulthood, when they emerge and repeat the entire destructive cycle. Regardless of the type of invader, if left untreated, insect infestations can cause the affected shrub to die.

Insect Repellent

Rid the garden of a variety of insect pests with a simple, homemade garlic spray. Place 15 cloves of fresh garlic into the base of a blender. Add 1 qt. of water and puree until smooth. Then pour the liquid through a coffee filter to remove any remaining solids and transfer the solution to a plastic spray bottle. Use the spray to coat any affected foliage, evenly covering both sides of the leaves. Reapply every three days until the insects vanish.

References

• Horticulture.net: Mallorn Plant of the Month: Rugosa Rose
• Ohio Department of Natural Resources: Rugosa Rose
• National Sustainable Agriculture Information Service; Use of Baking Soda as a Fungicide; George Kuepper, et al., November 2001
• Colorado State University Extension: Plant Talk Colorado- Pesticides: Natural Products
• "New Complete Guide to Gardening"; Susan A. Roth; 1997