Look out for rose rosette
Based on the number of questions the Johnson County Extension office is receiving I thought it would be a good idea to re-run a column from last summer on rose rosette. This is a nasty rose disease that has no cure. Removal of infected plants is a must. It is also important to point out that there is much misinformation about this viral disease spreading through the gardening community. Here are the facts and guidelines to follow when dealing with rose rosette.
Roses have always been America’s favorite plant, whether being delivered in a fresh arrangement from the florist or grown in the home garden. These beauties have undergone a revival, as we quickly switched from growing the higher demanding hybrid tea roses to the trendy easy care shrub roses.
For years we battled the foliar disease black spot with timely fungicide applications until the easy care roses came along. These roses were less susceptible and our problems seemed resolved. Now, there is rose rosette.
Rose rosette is believed to have been unfortunately introduced into the United States in the 1940’s and has slowly evolved. It is now our number one rose-growing problem. Learning to identify this dreaded disease is the key to its control and stopping its spread. This viral disease can appear in the following ways: • rapid stem elongation • leaf distortion • leaf reddening • leaf chlorosis with yellow mosaic patterns • abnormal narrow leaflets or smaller leaves than normal • thickened stems • excessive lateral bud development commonly referred to as witches broom • excessive thorn production
Basically, if you have a rose cane that grows more robust than the other canes, is reddish-purple, covered in thorns, develops numerous stems from one spot, or the flowers do not form properly you may have rose rosette.
Rose rosette is transmitted from plant to plant by an airborne mite. This microscopic mite carries the pathogen that causes the disease. This mite feeds on the juices of the plant injecting the disease. As it reproduces this tiny mite moves to the upper portion of the plant where wind currents carry it, and, as luck would have it, many of them fall onto our beloved roses.
Since rose rosette is a viral disease it moves within the cellular layer of the plant. Just like viral diseases in humans, viral rose diseases are difficult, or in most cases, impossible to eradicate. Controlling the mite is next to impossible because as soon as it lands on your happy plant it starts feeding, which passes along the problem.
Here is the bottom line in this dreaded disease. First, the mite cannot be controlled, or its movement stopped. And second, once the plant is infected there are no control measures. So the only effective control is to remove the plant immediately. By removal I mean dig it up, put in a bag and throw it away. (DO NOT put it into your compost pile!)
Based on how rose rosette spreads in the sap of the plant, it is recommend to sterilize your pruning shears when pruning roses. Simply spray the shears with either a household product such as Lysol or rubbing alcohol. Unfortunately, many unsuspecting gardeners, not realizing they had a problem, aided in the spread through pruning. That is why it is important to inspect your roses and remove infected plants.
There is one silver lining with this disease and that is once the diseased plant is removed new healthy roses can be replanted in the same location. It might be wise to wait a few months or until the next growing season to replant.
Johnson County Extension has been seeing this disease in the Kansas City area for maybe 10 years. But this year we are noticing and identifying the greatest number of samples ever. Now is the time to be on the lookout for this problem. If you need assistance in properly identifying the problem contact your location extension office or post a suspect picture to The Kansas City Star Garden Blog.
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