If you don’t gather them today, at least inspect them. They may be infected by rose rosette virus (RRV).

Rose rosette disease can be tricky. Its transmission involves three players: a virus, which is vectored by an eriophyid mite (Phyllocoptes fructiphilus), and the wild and sometimes invasive multiflora rose. For rose rosette disease to be successful, those three elements must be present. To break the cycle of this disease, eliminate one of the trio. Sounds easy. It’s not.

It’s believed that all cultivated roses are susceptible to the disease; this includes shrubs, hybrid teas, floribundas, grandifloras and miniatures. So even if there’s no evidence of multiflora in the immediate area, other roses may already carry the pathogen and can transmit it to your presumably clean stock. Once that happens, removal and destruction of the affected plants is your only option.

The brownish red panicle of an affected rose stands out against the normal flowers and healthy foliage of an adjacent plant.Photo courtesy James W. Amrine Jr., West Virginia University; Bugwood.org

What to look for

Symptoms of rose rosette disease can be difficult to recognize and confirm, as some signs mimic normal new growth. Many rose varieties are known for their richly colored young foliage, with leaves emerging a deep red to purple in spring. These generally turn green during the growing season, so if a plant continues to display intense red foliage throughout summer, it may have been infected.

Flushes of massed, tangled growth, similar to a witch’s broom, can signal the presence of rose rosette virus. This may be more evident in plants that have been infected for more than a year. Infected plants may display unusually large masses of distorted buds, most of which fail to open. Reddening and/or flattening of the cane can occur. Excessive thorn growth is an obvious sign.

Several of these symptoms appear similar to the signs of herbicide damage – which just adds to the challenge of confirmation.

Plants infected with RRV will decline and eventually die, but the disease may not be fatal for three to four years, by which time nearby plants may have been affected. Some speculate that rose rosette disease has become widespread in recent years due to the popularity of mass plantings, positioning plants close enough together to give the mite – which cannot fly, but can “balloon” on the wind – easy access to its next victim. So vigilance is key.

This plant shows the telltale dense flush of intensely colored young foliage, plus a mass of distorted flower buds.Photo courtesy of Sandra Jensen, Cornell University; Bugwood.org

How to manage rose rosette disease

Ultimately, the rose rosette virus is fatal. Once a plant is infected, it will not survive, so management of the disease is about preventing its spread to other plants.

Scouting for symptoms is vital to the long-term survival of nursery stock or landscape installations. It’s a good idea to inspect plants before they’re purchased, and take a look at neighboring plants, as well.

Roses have thorns, but this excessive growth is a sure sign of rose rosette disease.Photo courtesy of John Hartman, University of Kentucky; Bugwood.org

Although selective pruning of affected canes has been suggested as a possible means of management, this has proved – so far – to be ineffective. If signs of the disease are detected, the affected plants must be rogued. Many plants infected with RRV may remain asymptomatic; it’s a good idea to remove plants immediately surrounding them, providing a safeguard against further infection. Rogued plants should not simply be removed from the site, but bagged where they stand prior to removal.

Miticides have been suggested as possible “cure,” but to date, these methods have been unsuccessful.

This is the ventral, or belly, view of a Phyllocoptes fructiphilus (eriophyid mite), as seen under an electron microscope. Spooky, no?Photo courtesy of Anatomy Department Archive, West Virginia University; Bugwood.org

The most effective way to fight rose rosette disease: Vigilance; early detection; roguing of affected plants.

There’s an excellent online resource at AmericanHort’s Knowledge Center, including a webinar and videos that help to explain the how’s, the what’s and the why’s. Go to http://www.americanhort.com, click on “Knowledge Center” and select Be In The Know.

Cover Photo courtesy of James W. Amrine Jr., West Virginia University; Bugwood.org. Rose petals: istock|EvelinElmest