Welcome to my zone 9a habitat garden near Houston, Texas.

Wednesday, April 24, 2013

Will the Knockout be knocked out?

Have you heard about the new threat to the plant that we thought was impervious to all threats? Yes, I'm talking about the Knockout rose.

The first Knockout was introduced in 2000 and quickly became a hit because of its toughness and its ability to produce masses of flowers over a very long period. Many people found it to be the perfect landscape rose. It did not suffer from blackspot. It was forgiving of neglect, more drought-tolerant than most roses, which has certainly proved a boon in many areas over the last few years.

It did, in fact, seem to be the perfect rose for the lazy gardener. Since 2000, many other colors and varieties have been added to the original single cherry red, and many of us have happily added the plants to our gardens. At present, I have some of the single reds, one double red, some yellows, and pinks in my garden. They all perform well for me, although the yellows perform less well than the others. To lose all of these plants would leave a very large hole in my landscape, but that's what a recent article by Steve Bender in Southern Living magazine warns us could happen.

I was alerted to the article by my blogging friend Annie in Austin, and I read it with growing dismay. The disease that is already devastating Knockouts in some areas poses a threat to all roses, and I have about forty roses in my yard.  This could potentially be a knockout blow for all of them.

The disease that is causing all this angst is called rose rosette disease. It is a virus that is spread primarily by a tiny mite. It causes medusa-like bunches of bright red shoots on the plant. These shoots produce flowers that are very distorted and un-rose-like. Eventually, the plant begins to die back. Once the disease starts on an individual plant, that plant is a goner. There is no known cure for the disease. The best prophylactic action is to rip any diseased plant out immediately, bag it, and dispose of it.

Ironically, the disease was first seen as a savior - a weapon in the fight against the wild Multiflora rose which had escaped to become a highly invasive species in many parts of the country. Rose rosette disease was able to wipe out many of the stands of Multiflora when all else had failed. The problem was, when the virus ran out of wild roses to attack, it made the jump to gardens and public landscapes. And what is the most commonly used rose in large public landscapes these days? Knockouts, of course.

Formerly believed to be impervious to diseases, the Knockouts proved vulnerable to the tiny mite and the virus that it carries. The disease has now spread from the Northeast to the Midwest and down to South Carolina and northern Georgia. It has been seen in Alabama and northern Mississippi and even as far west as Fort Worth. The disease seems to thrive in drought conditions, which is probably not good news for the foreseeable future of roses in these areas.

Besides the Knockouts in my garden, the other roses that I have are all either antiques or David Austin roses. I planted them because they are all tried and true, very tough varieties. But then so are the Knockouts. To see all of this beauty felled by a tiny mite and a tinier virus would be a very sad thing.

Pink Knockout rose in my garden this spring.


  1. OMGosh, my husband just planted about 10 more knockouts in the yard. I already had a few mixed with my other roses. We are in south Alabama, thanks for the warning, I have never heard of this. Now I will know what to look for, hopefully we won't get it!

    1. It seems to thrive in dry conditions, so I guess we need to hope for rain and humidity!

  2. Very sad :-( As of now, we don't have any roses in the garden but I always love roses and it will be sad if this threat comes to fruition here.

  3. I had not heard of this, and it does sound very distressing. I don't have any knockouts, but I do have a few shrub roses and ramblers. I guess I won't be adding any roses to my garden while this situation sorts itself out.

    1. It was news to me, too. It's somewhat surprising that it hasn't become more widely known, I think.