Rose rosette disease
Photo courtesy of Mary Ann Hansen, Virginia Polytechnic Institute and State University; http://Bugwood.org
It sounds like you're repeating yourself, but rose rosette disease (RRD) is no joke. Initially believed to be a scourge limited to Rosa multiflora - which, considering the noxious nature of multiflora rose, might not be a bad thing - the devastating disease has been blooming, so to speak, for the past couple of years. Although it was first discovered in the 1940s, it has made its presence increasingly known in rose gardens and production sites in the eastern U.S.
What it looks like
Symptoms can range from what appears to be a flush of new growth to grotesque mutations that disfigure the plant. The most easily spotted signs of a rose rosette attack are:
- increased growth and/or rapid elongation of shoots
- new leaves and twigs have an abnormally bright, rich red color
- leaves may be distorted, curled or twisted
- an overabundance of foliage may be produced
- spiral pattern of cane growth
- canes produce excessive, red-tinged thorn growth
- atypical flower coloration, such as mottling
- deformed buds and flowers
Witches' brooms are a sure sign of rose rosette infestation, although at first the odd growth may appear to mimic the effect of herbicide drift. Where canes overproduce thorns, the growth may be so excessive that stems are covered.
How RRD is spread
The disease is thought to be caused by a virus - rose rosette virus or RRV - vectored by a tiny eriophyid mite, which is wingless but can be distributed on the wind. If shrubs are densely planted and leaves or canes are touching, the mite can crawl between adjacent plants. Grafting also may spread the virus.
Once the virus is introduced to the plant, it becomes systemic - and although it's not soil-borne, it may lie dormant in the remnants of roots from roses that have been infected and removed.
What do to if plants are affected
A few steps can be taken to prevent the spread, such as removing multiflora roses growing within 100 yards of cultivated varieties and spacing new plants so that the leaves and canes of one plant do not touch another.
While early detection is key to stopping the spread of rose rosette disease, the unfortunate fact is that although the cause of RRD has been identified, roses with symptoms cannot be cured.
Infected plants must be dug up immediately - and that includes all traces of root. All affected plant material should be bagged and removed or burned, where permitted. During removal, take care not to allow infected plants near healthy shrubs. Should new growth appear where infected shrubs had been removed - indicating that not all the roots were removed - immediately remove and destroy it.