Update on Rose Rosette Disease

Rose Rosette Disease is thought to be caused by a virus that came over to the United States in the 1800s with Asian wild roses.  Many of these roses were planted by settlers all over the United States and have become naturalized.  Rose Rosette Disease is now infecting cultivated roses throughout the United States, but especially in the South.

Eriophyid Mite

Rose Rosette disease is caused by a virus (Emaravirus sp.) that is spread by a very small, eriophyid mite.  This mite is so small you need a microscope to see it.  However, it certainly is big enough to cause trouble.  The wingless mite is blown on one rose bush, feeds, then is carried by the wind to another rose bush.  The problem with this is, in addition to damaging the rose bush, the virus is injected into the plant along with the mite’s saliva. 

Spreads Virus

The virus then attacks the foliage and roses and kills the infected rose in two to three years.  Unfortunately, since rose rosette is caused by a virus, there is currently no treatment for it.  The infected rose bush must be dug and destroyed.  When digging out the rose bush, it is vital to get every last root out.    If a new rosebush is planted where the other died, the pieces of root can infect the new rose, too.

Symptoms of Rose Rosette

The symptoms of rose rosette disease are most severe at the tender ends of the rose cane.  First, the underside of the leaves turn red.  Then the bush grows a witches broom at the ends of the rose cane. This is followed by a lot of growth on the vegetative shoots.  These shoots are typically more succulent that normal and are colored in various shades of red.  Leaves often become deformed and turn yellow and red.  As the disease progresses, leaves become very small and most lateral buds grow, producing red shoots that are very short.  The disease makes the rose very vulnerable to freeze damage.  It can also mimic herbicide damage.

Mite Lifecycle

The female mites can lay one egg a day for about thirty days.  The young hatch in three to four days and start eating.  They can reach adulthood in a week, depending on the temperature.  There are many generations each year.  When it starts to get cold, the females move to overwintering sites.

Use Caution May Through mid-July

The months of May through mid-July when the plants are actively growing are when the disease is more easily transmitted.  Symptoms start showing up in mid-July.  It is important to remove any bush with symptoms and wrap the bush in a garbage bag, then deposit it in the trash.  Do not compost sick roses as that just spreads the disease.

Prevention

Since the mite is spreading the virus, one way to stop the problem is by pruning away two thirds of the rose bush in late winter.  Then spray the remainder of the rose bush with horticultural oil, paying special attention to the tips of the rose bush.  Then spray the rose bush with oil once a week from June to July.