I wrote about this disease six years ago when it was first being reported in southern states, but this is the third year I am seeing it quite commonly on many wild multiflora roses in my neighborhood and elsewhere in our region.
In fact, it appears the disease has killed a significant percentage of the multiflora roses in Greene and surrounding counties. Some overgrown fields I drive by every day had dozens of multiflora roses, and now, they are almost all dead.
As an outdoorsman, who has shed too much blood from their sharp thorns, I am delighted to see them go! Multiflora rose is also considered a serious “invasive species” and although no plant is inherently evil, this one has more downsides than pluses. It can turn old fields and hedgerows into impenetrable, thorny, thickets in only a few years.
The disease symptoms on multiflora rose are striking, so diagnosis is pretty easy. Symptoms of Rose Rosette disease on other species are more variable, depending on the species or cultivar of rose affected.
This variability can complicate diagnosis. Some of the more recognizable symptoms include rapid elongation of new shoots, followed by development of witches’ brooms or clustering of small branches.
Leaves in the witches’ broom are small, distorted, and may have a conspicuous red pigmentation, although red pigmentation is not a consistent symptom. Although not consistent on all infected plants, the red color is very noticeable. Canes on some species or cultivars develop excessive growth of unusually soft and pliable red or green thorns, which may stiffen later.
When this symptom is present, it is diagnostic for Rose Rosette disease. Symptomatic canes may also be noticeably thicker than the parent cane from which they emerged or they may grow in a spiral pattern. Flowers may be distorted with fewer petals than normal and flower color may be abnormal.
For example, flowers that are normally a solid color may be mottled. Buds may abort, be deformed, or be converted to leaf-like tissue. Infected rose plants often die within one to two years.
Rose rosette disease is caused by a virus, which is known to be transmitted by a mite or by grafting. Cultivated roses planted downwind of infected multiflora rose are especially at risk because the mite vector travels on wind currents from infected to healthy plants. Some growers have observed symptoms on previously healthy plants within four weeks of being planted downwind from diseased multiflora rose.
The causal agent (virus) of Rose Rosette disease is not soil-borne, so it is possible to successfully plant healthy roses in beds where diseased plants have been removed; however, the pathogen may persist in old root pieces that remain in the soil from previous diseased roses.
If plants regrow from these old root pieces, as multiflora rose is apt to do, they can serve as an infection source for healthy plants. Therefore, it is important to remove old plants thoroughly and ensure infected plants are not allowed to regrow from old, infected root pieces.
No effective control is available for rose rosette in existing, diseased rose plants. Infected plants need to be removed and destroyed at the first sign of symptoms.
Reach Bob Beyfuss at firstname.lastname@example.org.