Something (not so) funny going on with Roses

As a longtime Master Gardener, one of the interesting and enjoyable parts of my volunteer service has been helping home gardeners identify and remedy, if possible, problems with plants they are growing in their home landscapes.

Lately, we’ve been getting more questions about what’s going on with roses, especially the very popular ‘Knock Out’ series, but not limited to ‘Knock Out’.  Gardeners have been noticing strange, bunchy growth that just doesn’t look quite right.  Their roses seem overall fairly healthy, but they are finding new growth that doesn’t change coloration as usual from red to green.  New growth remains red, and there may be other changes – extra thorniness (almost like a bristle brush), thickened stems (especially if a thick stem is growing from an older, thinner stem), and leaves that are narrower than normal.  All these symptoms are not necessarily visible at the same time.  In many cases, the rose bushes look pretty normal, but there is part of it that looks, well, different.

So, what’s going on?  Research has confirmed that roses displaying symptoms as above are infected with Rose Rosette Disease (RRD), a disease (probably a virus) transmitted by a type of mite.  Unfortunately, this is not your grandmother’s spider mite.   Spider mites afflict roses every year, especially in hot, dry weather; luckily, there are effective controls to manage spider mites.

The mite causing the problems we are now seeing in roses is an eriophyid mite, quite different from the common spider mite, and only visible under a microscope.  When this mite feeds on a rose, it transmits the disease, which then spreads throughout the entire rose bush.  When the bunchy, strange growth appears, it is so tempting to just cut it out.  I wish that would work, but it doesn’t, as the disease remains in the plant and will continue to show up as the plant grows.  There is no cure or treatment as yet, and, as far as I can tell, once infected, the result is the decline and death of the rose.  The gardener’s only option is to remove the rose and as much of the root system as possible.  The rose must be bagged tightly and discarded if burning is not an option in your area.  Do not replant another rose in the same spot, but select another type of plant.

Are all roses susceptible to RRD?  Unfortunately, yes, but some may prove to be somewhat resistant.  RRD has been reported in the United States since the 1940’s, but there has not been a lot of research into it.  Chances are we are seeing it in ‘Knock Out’ roses now because so many have been planted.

In that case, what’s a rose grower to do?  First, monitor your plants for signs of trouble.  Second, do not use herbicides (weed killers) of any sort around your roses; herbicides can damage roses and produce distorted growth that may be confused with RRD.  Third, when planting roses, give them plenty of room so they don’t touch; eriophyid mites can’t fly, but they can stroll to the next plant.  Fourth, should you have any questions regarding your roses, call Ken Creel, Regional Extension Agent, Home Ground Horticulture, Alabama Cooperative Extension System, at 256-532-1578 or 256-382-1554.  He is trying to track RRD and would like to be notified should RRD be suspected.  Fourth, read further so you will know what to look for.  An excellent resource is available from the University of Virginia Extension (http://pubs.ext.vt.edu/450/450-620/450-620.html).

As a rose gardener myself, what am I going to do?  Well, I just bought three more roses last weekend.  I’m going to plant them in my yard, give them plenty of room, and watch them grow.  Roses are a great landscape plant with a lot to offer – garden color, cut flowers, and sometimes fragrance – and I wouldn’t want to miss the opportunity to enjoy them.

Gigi Bullman is a Master Gardener, member of the local and national rose societies, and a member of the Madison Beautification & Tree Board.  According to her husband, it is her mission in life to pack as many roses and other plants into their home landscape as possible, thus helping the local economy by keeping the nurseries in business.