Whatís Killing the Roses?

Betty Jakum
Adams County Master Gardener

(5/9) Iíve never been much of a rose lover. My gardening preferences tend toward the easy, free-flowing jumble of cottage gardens, where one might find an old-fashioned cabbage rose or heirloom variety but not one of todayís elegant, formal roses.

For me, most of todayís rose varieties are just too finicky and challenging to grow. They are hungry plants, and constant attention needs to be paid to feeding them properly. Also, do I need to mention all the insects and diseases that chip away at their health? Black Spot on leaves is ubiquitous, causing leaves to yellow and fall and creating extra work for gardeners who have to remove them or risk spreading disease. Roses also suffer from powdery mildew, rust and canker. Insects are another bother for roses and include thrips, rose bud borers, leaf-cutter bees, aphids and spider mites, these later two sucking the juices from leaves and flower buds and generally weakening the bushes.

Unfortunately, my husband thinks otherwise, so over the years our gardens have grown roses, and not without their share of problems, I might add. I guess itís been a dozen years or more now that I noticed something odd on a lovely yellow climbing rose we had. While most of the plant and its flowers looked okay, I could see places sprouting angry red canes growing in a spiral pattern. Other nearby shoots were elongated with excessive thorniness. In spots, numerous lateral shoots, mostly red and known, I was later to learn, as witches broom, clustered at the tips of the canes. The abnormal growth was very brittle and snapped off easily at the slightest touch.

While in an odd way not altogether unattractive, I nevertheless figured what I was looking at meant trouble. After quite a bit of research, I found out the condition was something called Rose Rosette Disease, believed to be caused by a virus for which there is no effective control in existing diseased roses. By the time it was through with us, we had lost all our roses, save for one scraggly specimen that grew largely ignored for years in an old, untended garden.

Rose Rosette Disease (RRD) has existed in the United States since around 1941, and its spread is linked to the history of the multiflora rose that was introduced from Japan in the 1860s as an ornamental and as rootstock for ornamental roses. For about 30 years beginning in the 1930ís planting multiflora rose was recommended by the USDA Soil Conservation Service for erosion control, strip mine reclamation, as a bird sanctuary and food source, as a living fence for cattle and as a crash barrier on highways. This turned out to be a horrible mistake as it spread rapidly and is now considered a noxious weed.

Multiflora rose is extremely susceptible to RRD, killing infected plants in two years. Itís so successful that itís been considered for use in controlling this pesky weed. Unfortunately, RRD can also infect and kill garden roses. Generally believed that the causal agent is viral, it is spread from plant to plant by extremely tiny, wingless eriophyid mites blown from plant to plant by the wind. RRD is also spread by grafting.

RRD symptoms on garden roses include rapid stem elongation, an overabundance of thorns (hyperprickliness), and susceptibility to powdery mildew. Some cultivars and species show red-to-pink-colored leaves; others do not. While many roses have red-colored new growth, it matures to green. With RRS, it stays red. Short, deformed canes grow, often red in color, and produce more buds than usual and smaller than normal or badly distorted leaves. Leaves are small and may not feather out beyond the stem. Flower parts on infested canes are distorted, sometimes leaf-like, while other canes on the same plant produce normal flowers and fruit.

Chemical control of RRD is difficult, but there are some measures to take to protect roses. Monitor nearby populations of multiflora roses, especially those upwind of your garden. Because they are so susceptible, they can act as an early warning signal for the diseaseís presence. In my particular case, I eventually found an abandoned pasture not far from my property thatís overgrowth of multiflora rose was practically wiped out about the same time my roses were dying.

If possible, eliminate multiflora roses growing within 300 feet of cultivated roses. Remove and destroy garden roses that show symptoms of RRD as soon as you notice them. Bag discarded rose plants and put them out with the trash or burn them rather than composting them.

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