Common Knock Out Rose Problems: Diseases Of Knock Out Roses

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By Stan V. (Stan the Roseman) Griep
Retired American Rose Society Consulting Master Rosarian – Rocky Mountain District

Knock Out rose bushes are known for being extremely disease resistant as well as being nearly carefree. However, even these fine rose bushes can, due to climatic and poor care/conditions, succumb to some of the same diseases that plaque other rose bushes in our gardens and landscapes. Let’s learn more about these potential problems with Knock Out roses.

Knock Out Rose Diseases

There are five common diseases of Knock Out roses and one serious virus that they now must also deal with. The five common Knock Out rose diseases are:


A well fed, well hydrated and actively growing Knock Out rose bush will be able to fend off these foes very well. However, if we add into the scenario the stresses of injury (perhaps due to a weed whacker being used a bit too close to the bushes), heat stress, lack of water stress, poor soil (perhaps due to poor drainage or just poor soil in general), or insect and mite invasion, the rose bushes become a far more easy target for diseases to attack.

Also, a minimal care rose bush does not mean a “no care” at all rose bush, just as “disease resistant” does not mean a disease free rose bush. The Knockout roses, just like their counterpart roses, do need some care.

Earlier I mentioned one other disease problem that Knock Out rose bushes have to deal with now, that heartbreaking disease is called Rose Rosette disease (RRD). The RRD virus is a nasty incurable virus. Once the rose bush contracts the disease, it is best to dig it out and dispose of it, then obtain another rose bush to plant in its place. Planting another Knock Out rose in the same location should be fine, though I do recommend replacing the planting hole soil with a good bagged garden soil mix (preferably a mix that has compost in it and little to no added fertilizers). Here is a listing of symptoms of the Rose Rosette virus for you:

  • New growth on many rose bushes is red and hardens off to green as the leaves and canes mature. If infected with the RRD virus, this mature growth will remain red.
  • An abundance of short shoots near the tops of the canes (aka: witches broom). Please keep in mind that this particular symptom can be caused by herbicide injury, so if you or a neighbor has been applying an herbicide, the drift of the spray could cause this. Be sure to check for other symptoms!
  • Distorted, underdeveloped leaves.
  • The affected canes may be thicker than the section of cane they are growing out from or they may also appear to be growing in a spiral pattern.
  • The virus infected canes may have an unusual amount of thorns. Totally different from the rest of the canes on the bush.
  • The bloom buds may stop midstream and fall off, or the blooms may be deformed or mottled.

Treating Issues Affecting Knock Out Roses

For most problems with Knock Out roses, the spray application of a good fungicide at timely intervals would be considered wise, along with, of course, keeping an eye on the soil moisture levels and nutritional needs of the rose bushes. Any particular Knock Out rose problems that may arise with any rose bushes or other plants is far easier to manage if noticed early on. In my rose beds, I try to keep applications of any pesticide to a minimum, and when I do need to make an application of a pesticide, I follow three simple rules:

  • Positively identify the problem. There is nothing worse, as well as possibly more stressful for the subject rose bush or plant, then to make multiple applications of various pesticides in an effort to solve a given problem.
  • Thorough watering of plants. Water rose bushes well the day before making any pesticide application. This includes feeding them too!
  • Use the most Earth-friendly product first. Try organic approaches first before moving on to more harsh chemical treatments and only if the problem is critically severe and the first application simply is not gaining any ground on the problem in a reasonable amount of time.

Please be sure to look up each of the diseases mentioned herein on our Gardening Know How website, so that you will be better educated on what to look for with each of the diseases mentioned. Again, early identification of a problem makes it far easier to manage.

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