Is Knockout Rose Down for the Count?

April 21, 2013 | By | Comments (60)
Knockout rose

Enough color to knock your socks off — that’s ‘Knockout’ rose. Photo by Steve Bender.

Introduced in 2000, ‘Knockout’ rose quickly became the best-selling landscape plant in the country. It had everything — showy, continuous blooms; compact growth habit; tough-as-nails constitution; and, best of all, no need to spray forĀ black spot disease. But now, nature has tossed green kryptonite into Superman’s garden. And ‘Knockout’ rose may just get its bell rung.

A Deadly Threat
‘Knockout’ rose (the original single red, shown above, plus a bunch of newer colors) owes its uber-popularity to the belief that it’s the first “no maintenance” rose — perfect for the lazy gardener in all of us. People think it needs no watering, spraying, pruning, or fertilizing — EVER. It’s like an actual living plastic plant. You just stick it in the ground and it will bloom, bloom, bloom with zero care from you. How marvelous.

Unfortunately, this belief is dead wrong. ‘Knockout’ does need water, fertilizer, and pruning. And now it’s facing a disease so serious that its very survival is in question. Rose rosette disease.

Rose rosette

Rose rosette disease. Photo: nicolewardukblogspot.com

This is what rose rosette looks like and it’s not pretty. A formally healthy plant starts producing Medusa-like bunches of bright-red new shoots. The shoots bloom, but the flowers look distorted. As rose rosette spreads through the plant, the rose gradually dies back, until it completely croaks. Down for the count.

What Causes Rose Rosette?
Rose rosette is caused by a virus first discovered in the western U.S. around 1940. The virus is principally spread by tiny eriophyid mites — so tiny, in fact, that they literally blow into gardens on the wind. When they feed on a rose, they transmit the virus. At that point, the jig is just about up.

Now here’s a surprise. There was a time when rose rosette was considered a savior, not a plague. Any of you remember the infamous “living wall,” aka the multiflora rose? A vigorous, arching import from Japan, it produced pretty white flowers in spring and thousands of small, bright-red rose hips in fall. It grew so thickly that highway departments in the East and Midwest actually planted rows of it down highway medians. Even a tractor-tractor couldn’t smash through. Cattlemen also used it to contain cattle.

But you know what they say about good intentions. Birds ate the red rose hips and spread multiflora rose everywhere. It proved to be an awful, noxious weed. States banned it, but it was too late. The entire eastern U.S. was destined to be smothered by the stuff, unless a control could be found.

It was. Rose rosette disease.

Wahoooo!!! Rose rosette killed multiflora rose faster than a van filled with nuns kills a good kegger. Unfortunately, when rose rosette ran out of multiflora roses, it looked for something else to feast on. The target? ‘Knockout’ rose and other shrub roses. The first ‘Knockout’ roses to show symptoms were located where the highest concentrations of multiflora roses were growing — the East and Midwest. ‘Knockout’ roses in the South have it now too.

Can Anything Stop Rose Rosette?
Because rose rosette is caused by a virus, it eventually spreads internally to every part of the plant. Promptly removing the bright-red shoot clusters by cutting through healthy green wood below them may save a rose. But once a rose gets full-blown rose rosette, turn out the lights. You must pull up the rose, roots and all, bag it, and throw it out with the trash. Spraying will not work.

Conard-Pyle, the respected Pennsylvania nursery that introduced ‘Knockout’ roses, suggests pruning back the plants by 2/3 while they’re dormant in late winter to remove any overwintering mites and eggs in the bud crevices. This is especially important for large landscape plantings of ‘Knockout,’ because the more bushes you have, the more mites you have, and it’s easier for the virus to spread.

Now For Some Really Bad News
According to Grumpy’s sources, most rose species and their selections are vulnerable to rose rosette — not just ‘Knockout.’ So if your love your roses, keep your eyes peeled for weird-looking, bright red shoots. Don’t leave yourself open to a ‘Knockout’ punch.

COMMENTS

  1. A Better Rose Than Knock Out | Southern Living Blog

    […] Is ‘Knock Out’ Rose Down for the Count? […]

    July 30, 2015 at 10:00 am
  2. Penny Stuart

    I bought 2 double knockout rosebushes couple of months ago and one of them is doing fine the other one was quite dead think I can do to revive it?

    July 29, 2015 at 3:28 pm
  3. Steve Bender

    Mf Leahy,

    If this is indeed the case, then your state department of agriculture needs to be made aware of it, as selling diseased plants is against the law.

    July 1, 2015 at 10:15 am
  4. Mf leahy

    I was at my local Home Depot garden center in Plano TX this morning and saw that they have “Knockout Roses” for sale that clearly show they are already infected with the Rose Rosette Virus. When I asked if they were aware of it they simply yes we are.. yet the continue to have them on display for sale to a poor unspecting buyer……….. and contributing to the spread of the virus. How irresponsible of Home Depot…

    June 27, 2015 at 12:06 pm
  5. Steve Bender

    Helen,

    I have never heard of raspberries being affected.

    May 30, 2015 at 7:12 am
  6. Steve Bender

    Derek,

    I don’t know of any preventive method that’s been shown to work.

    May 30, 2015 at 7:10 am
  7. Helen

    My neighbor bought a Knockout rose and it had the virus as it began showing signs right away. I asked her to dig it up and she did. The next spring all 15 of my roses, some single and double Knockouts, showed signs of it. Now my raspberry bushes have bright pink stems. I have read that this virus is only on roses but I have some other plants that look odd this year. Have you heard of it being spread to raspberries by using the same clippers or such? I know the mites are rose specific, but perhaps the virus isn’t. Raspberries are closely related to roses, after all. As for the other plants, I am not sure what is going on. I have been gardening for more than 30 years and seeing things I have not seen before. Like plants that don’t get red leaves are getting red leaves and stems. Maybe I am just paranoid. I regret the day I ever saw a Knockout rose.

    May 27, 2015 at 3:30 pm
  8. Rosemary

    Buying new knock out I. Noticed. Ma my
    Frail looking thorns and skim to the flowers is this the start of the disease?
    When the bush is on disease, does this make the soil totally alkaline true or false
    Are there any horticulturist rosarians who would come to my house and let and see for themselves if my knockouts are fully diseased

    May 25, 2015 at 2:14 pm
  9. Deby Wine

    I had ! (ONE!) rose and it died. I had planned to put many around my community, as the HOA President. Would never buy another, ever.

    May 21, 2015 at 2:04 pm
  10. Wilford Lester

    the knockout should not be sold thay are still beingsold ihave planted about 100 i have lost about 10

    May 21, 2015 at 11:58 am

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