Plant Pathology: Rose Rosette

Plant Pathology: Rose Rosette

Rose Rosette disease

Rose rosette is a novel threat to seemingly all cultivars of roses, even those previously known and used specifically for their disease resistance. Losses due to this disease have been documented on home and commercial landscapes, in nurseries as well as botanical gardens. Look for symptoms at the beginning of the season, but continue to monitor throughout the summer and fall as symptoms intensify as the season progresses.  Rose rosette disease symptoms include: increased shoot elongation, reddish discoloration of shoots and foliage, abundant clustering of small shoots (also called “witches broom”), spiraling growth of main stem, less space between leaf shoots, distorted leaves, prolific thorns, mottled blooms, deformed buds or flowers and decrease in winter hardiness.

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Illustrated here is the discoloration and deformation of leaves and flowers due to rose rosette disease.

Rose-Rosette-Thorniness

This specimen exhibits the overproduction of thorns.

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Shown here is an example of the red discoloration and twisted growth of shoots.

 

Disease Development

A virus has been identified as the cause of rose rosette disease, aptly names “rose rosette virus” or RRV. It appears to be vector borne, transmitted via eriophyd mites. These microscopic, flightless mites crawl between plants using closely planted or touching vegetation as a bridge, they can also be transported on a gust of wind or by hitching a ride on another insect. Adults are capable of overwintering on the stems of roses, they will find their way up to developing shoots in the spring to lay their eggs. Introduced from Japan and now considered invasive and noxious, multiflora rose, is very susceptible to RRV acting as a primary host. Rose cultivars growing near multiflora rose are at high risk for infection.

Initial stages of RRV are very difficult to diagnose, early stages can be easily confused with other problems or be too mild to detect. Plants with abnormalities or grow in a susceptible site should continue to be monitored. Alert your arborist to any concerns you may have.

Disease Defense

There are some simple things you can do to protect your landscape becoming infected with RRV or spreading the virus further. Make sure to buy any new roses from a reputable nursery and inspect all plant material for signs of disease prior to purchase. If possible, remove any multiflora rose on your property or within 100 yards. If this is impossible, be careful not to plant any new rose plants downwind of the multiflora roses. When installing new plant material space them accordingly so as not to create a vegetative mite freeway, account for future growth. Always consult your arborist with any questions, they can provide guidance on site selection, plant placement, cultural preventative measures and other possible treatments.