Rose Rosette Disease

 

Rosa rugusa in the Tea Bed at Herb Garden

In Franklin County with agricultural land and dairy farms in abundance, multiflora rose was once viewed as a valuable addition to the landscape. Now viewed as an invasive species, it is under attack from a virus. Landowners and managers who have battled this invasive plant for years celebrate; however, rose growers lament.

Cultivated roses planted downwind of the infected multiflora rose plants are especially at risk when wind currents move mites that carry the virus. With mite populations peaking in September, home gardeners need to survey their roses. Once infected, roses can show signs of the disease in as few as four weeks. There is no known treatment or cure for infected plants.

Jeff Mulhollem of Penn State University notes in a recent article that although brought to North America in the 1700s as rootstock for grafting ornamental roses, it was quickly recognized for other values. From the 1940s through the 1960s, it was touted as a 'living fence' that kept livestock confined. Conservationists espoused it as the "ultimate conservation plant" that was easy to grow, held soil, and created dense wildlife habitat. "Some departments of transportation thought the tangles of thorns were useful as crash barriers."

Each flower on the bush produces a rose hip, a valuable source of Vitamin C and flavoring. Each rose hip contains seven seeds. Every year a single multiflora rose plant produces up to half a million seeds. While these seeds can lie dormant for up to 20 years, often birds eat them and spread the seeds over larger areas.

"Multiflora rose is one of the best - or worst - and most visible, examples of an invasive plant thriving in Pennsylvania's landscape. But for better or worse, a disease increasingly is infecting and killing the thick stands across the state," according to Mulhollem.

 What is Rose Rosette Disease?

This disease, only found in Rosa species and hybrids, is caused by a plant virus that is spread by eriophyid mites or during the grafting process. The mite is microscopic and tends to hid in buds, at the base of shoots, leaf axils or under leaf scars. The mites get the virus when feeding on infected plants and the disease is spread when the mite feed on a new plant. Although the mites only crawl short distances on rose plants they can be carried further distances to other roses on wind currents (leaf blowers, too), tools, gloves and clothing. Mites overwinter.

What does it look like?

Most often gardeners will first notice the quick elongation of new shoots, frequently displaying a cluster of smaller, distorted, red branches called "witches' brooms."There can be an excess of thorns on the stems and deformed flowers. Infected plants often die in one or two years; however, some plants may live as long as four years. Some researchers report that infected canes are more susceptible to damage from low temperatures.

What can home gardeners do?

Oklahoma State Extension notes that “research suggests that the virus does not contaminate the soil like some other pathogens if infected roses are removed from a site. The mites will die in about a day in absence of a host. However, they can survive on fallen debris.” Clean up is crucial. However, North Carolina Extension Service suggests a two year period before replanting in the same area.

Management Guidelines for RRD (compiled from several Extension Service sites):

·         Remove all the diseased plants from the landscape. Do not compost.

·         Discard all diseased foliage and all roots stock (roots left in the ground are still infected and could re-sprout) in the trash. Do not compost.

·         Clean the area of all fallen debris such as buds and fallen leaves and discard. Do not compost.

·         Clean all garden tools, gloves and clothing to avoid the continued present of mites.

·         Do not use leaf blowers near roses.

·         For new installations, do not overcrowd plantings. Use proper spacing. Prune to eliminate leaves touching between plants.

·         Consider mixed planting of roses with non-rose material to break the disease cycle.

·         Promote health and vigor with proper care (watering, fertilizing, controlling fungal diseases).

·         Scout and remove wild roses in the area and handle according to the guidelines.

·         Scout landscape roses in the area for symptoms and handle according to the guidelines.

 What about invasive plants?

Penn State's Mulhollem notes that "while some landowners will celebrate the loss (reduction) of multiflora rose, its loss is not a reason to reduce vigilance. At least one study has shown that the void left by its demise is rapidly filled by bush honeysuckle and, perhaps, autumn or Russian olive.

 "Some people suggest that we give up the fight against burgeoning invasive plants; others argue that we have to encourage more indigenous plants to support native insects, which feed our native species. If you want to keep invasive plant species at bay on your land, the sooner your act, the better. It is much easier to control a few plants."

 In Franklin County with agricultural land and dairy farms in abundance, multiflora rose was once viewed as a valuable addition to the landscape. Now viewed as an invasive species, it is under attack from a virus. Landowners and managers who have battled this invasive plant for years celebrate; however, rose growers lament.

 Cultivated roses planted downwind of the infected multiflora rose plants are especially at risk when wind currents move mites that carry the virus. With mite populations peaking in September, home gardeners need to survey their roses. Once infected, roses can show signs of the disease in as few as four weeks. There is no known treatment or cure for infected plants.

 Jeff Mulhollem of Penn State University notes in a recent article that although brought to North America in the 1700s as rootstock for grafting ornamental roses, it was quickly recognized for other values. From the 1940s through the 1960s, it was touted as a 'living fence' that kept livestock confined. Conservationists espoused it as the "ultimate conservation plant" that was easy to grow, held soil, and created dense wildlife habitat. "Some departments of transportation thought the tangles of thorns were useful as crash barriers."

 Each flower on the bush produces a rose hip, a valuable source of Vitamin C and flavoring. Each rose hip contains seven seeds. Every year a single multiflora rose plant produces up to half a million seeds. While these seeds can lie dormant for up to 20 years, often birds eat them and spread the seeds over larger areas.

 ~ Carol Kagan, Master Gardener

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