Outbreak of Rose Rosette Disease Detected on Hill

1918
Grosjean point to a "witches broom," blooms shrivelled and elongated until they look like the end of a straw broom.

Mia Grosjean started noticing it late last year. All over the Hill, the once-ubiquitous, beautiful rose bushes were starting to look different. Shriveled. Less joyful. “Like witches’ broom,” she described them.

Disturbed by the similarities she saw as she walked down East Capitol and Independence Avenue from her home near Lincoln Park, she began to do her own research.

Rose Rosette Disease (RDD)

What she learned didn’t comfort her. The witches’ brooms she had noticed throughout the Hill were a characteristic of Rose Rosettte Disease (RRD), an incurable horticultural disease that infects roses. Worse, it was obviously traveling down streets, infecting bushes as it went, destroying the Hill’s rosebushes.

Grosjean began leaving notes at homes where she spotted the tell-tale signs. But given the signs, she began to worry —some of the world’s most famous roses are just down the street at the United States Botanic Garden (USBG); further along, and even more famous rose bushes located just down Pennsylvania Avenue.

Mia Grosjean points to a bush showing symptoms of RDD.

“I started wondering, does the Botanic Garden know about this?” she said. “What about the White House?”

Jim Adams is Horticulture Manager at USBG and the former Supervisory Horticulturist at the White House. He said that RRD has been found in roses at the Botanic Garden for about 6 or 7 years. Adams has seen extensive rose rosette-infected plants in the Capitol Hill neighborhoods for at least the past 12 years, he added.

Telltale symptoms are distorted growth that is a reddish color, often with excessive thorns and leaves, he said, sometimes mistaken for herbicide damage or powdery mildew. But these signs only indicate the problem has progressed beyond help, the horticulturalist said.

“By the time the plant is exhibiting symptoms, it has already had the disease in its system for several years,” Adams said. “If a plant is exhibiting symptoms it should be removed and put in the trash, not compost.”

A rose-bush exhibits tell-tell signs of the highly contagious RRD. Note the shrivelled blooms, which look like “withces brooms” and thick stems and shoots, as well as excessive thorns.
A healthy rose bush is characterized by lush wide green leaves.

Proper Disposal Key to Stopping Infection

Adams emphasizes that if a gardener detects infected rose bushes, they should be trashed. Plants, roots and any twigs and leaves should be placed in the garbage —not the compost. That is to avoid the transmission of the disease, which Grosjean sees as a pandemic among roses.

That’s because the disease is transmitted by a very small insect called an eriophyid mite, which travels on wind currents and lands on host plants to feed on the leaves. “They pick up the virus from one plant and after they blow to another plant, they then infect it when they feed on it,” Adams said.

The debris itself becomes contagious, and if improperly handled, could go on to reinfect other plants, creating a vicious circle that is difficult to break —and might not be detected until it is too late.

Debris should be removed by hand, rather than using a leaf blower that might blow mites onto healthy plants. Trash should be placed in a sealed bag.

RRD is a devastating disease for rose bushes, but the impact won’t decimate our enjoyment of roses forever. While some believe that RRD makes soil unsuitable for years, Adams said a wait of only a few months is actually necessary to ensure the mites are cleared.

“The virus is not soil borne,” Adams said.

Protect Your Roses from RDD

Certain varieties of rose are more susceptible to the disease than others, Adams said. “Knock Out Roses are extremely susceptible to rose rosette disease and have been planted extensively by many home gardeners as well as developers,” Adams said, adding that multiflora is also susceptible but is also an invasive exotic that should be removed if it is growing near cultivated roses.

The best defense for keeping rose bushes free of the virus is to keep them healthy, said Adams.

”Generous spacing of plants, proper pruning, proper fertilization to keep healthy plants, as well as sterilizing pruning tools between use on plants,” are the prevention he advises. Most important is to avoid planting in particularly windy sites where the chances of mites blowing on them is greatest, the horticultrualist adds.

You can learn more about Rose Rosette Disease (RRD), how to spot it and what to do by visiting https://roserosette.org/

Learn about the United States Botanic Garden by visiting usbg.gov