So, you’ve fallen in love with Double Knockout roses! But what if they are susceptible to diseases?

So, you’ve fallen in love with Double Knockout roses!  And what’s not to love?  So many benefits and bigger, better blooms than traditional roses!

But chances are that whether you are considering the purchase of a Knockout rose or have already added one to your landscape, you’re curious about the diseases that plague the traditional rose varieties you’ve always known.

Can Knockouts be affected by the same plights?

Double Knockout rose bushes are extremely disease resistant. They’re much more resistant than traditional rose varieties.

Unfortunately, when you’re dealing with nature, beauty doesn’t equal perfection.  Under poor conditions, double knockout roses can still get hit by some diseases.

Let’s take a moment to learn about the five most common diseases that a Knockout rose can face, and how to prevent them all together!

The five most common diseases that could affect a Knockout rose are:

  • Rust
  • Black Spot
  • Botrytis Blight (Gray Mold)
  • Powdery Mildew
  • Stem Canker



Double-Knockout-RoseNamed for its orange, powdery appearance, rust is a disease common to roses that appears first under the leaves and soon spreads to the rest of the plant.  Rust is a fungal disease that spreads in moist air.

Black Spot

The appearance of circular black spots on the leaves or stem of a rose is known as the fungal disease Black Spot.  This particular rose ailment can quickly destroy an affected plant if left untreated.

Botrytis Blight

Sometimes also called Gray Mold, Botrytis Blight is a fungal disease that prohibits new buds from opening and seals them in a grayish mold.  Open rose blooms become covered with brown and/or yellow markings and petals become brown and droopy.  It spreads in cooler temperatures and moist air.

Powdery Mildew

Powdery mildew is a fungal disease affecting roses that causes a white, powdery substance to appear along the top and bottom of both foliage and stem, and occasionally even the on blooms themselves.  This disease prevents your Knockout from reaching its maximum height, and causes the affected leaves to become dry and eventually fall off.

Stem Canker

Pink-Double-KnockoutStem Canker is a disease caused by fungus that thrives in water and then gets into the canes of your rose through cuts in the stem’s skin.  Reddish brown in color, these cankers are small spots that crack and swell, eventually causing the stem — and all the foliage and blooms above it — to die.

Disease Prevention

Those don’t sound like much fun to deal with, right?  Then let’s get to the good news!  As you may already know, Knockout roses are hardier than other varieties.  So while these five diseases can happen, your Knockout is far less susceptible to them than other varieties may be.

You can ensure that your rose does not succumb to disease with the minimal effort of just a bit of preventative maintenance.

First of all, avoid watering in the evening when possible.  If you must water your roses in the evening, such as if temperatures or drought require it, take care to do so only at soil level.

89622591.y3BT17rA.FrankfortKnockoutscopy_01You should never purposely wet the foliage or blooms of your Knockout.  Moistening more than the soil is the easiest way to promote disease; avoiding it is the easiest way to prevent disease!

If at some point your Knockout does become affected by any of these ailments, you can prevent them from spreading and causing any further harm by simply trimming off any effected parts and disposing of them properly, and cleaning up fallen leaves and blooms regularly.

Don’t forget to clean your gardening tools well if used to prune a diseased rose.
Chemical solutions, such as fungicide, should be used only as a last resort.

Remember, when it comes to Knockout roses, prevention is better (and easier!) than any cure.

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12 years ago I was sitting around, talking with two of my favorite, fellow Plant Geeks. We were trying to figure out why so many, superior plant varieties were not available to the public and were seldom offered in Garden Centers. Instead, the stores sold less attractive, older varieties, proven to be disease and insect prone. They also sold the sprays and chemicals that their customers would eventually need. The Ah Ha moment hit us and a company was formed. We decided that we would only offer the highest quality plants that must be Easy to Grow.
  • smiley490s

    My knockout rose petals are curving under making spike looking petals. What is the cause?

    • AllisonTrees

      It could be something as little as fluctuation temperatures, which makes sense for this time of year. Many places around the country have cool mornings and hot afternoons. Although, it’s a sign of stress. It could be a sign of your roses getting a fungus, or having pests. Watch for discoloration in the foliage, leaf drop, or holes in the leaves, these will be indicators that you need any organic fungicide or insecticide.

  • lucy luu

    My beautiful bush is so un lively what happened how do I save it

  • Bill Harral

    My knock out roses are 4-5 years old. I prune and fertilize properly. For the past 3 years they ONLY bloom once in the Spring (I live in PA). They remain vibrant until the Fall but never bloom again. I’m told this is cause by a mite. True? Remedy? Many thanks.

  • Joe galloway

    I have two knockout rose bushes and they have become sick I live in crockett tx and the temp is everywhere through out the week ,as yall can see in the photo (yellow and black ,on leaves ) iam lost I have no idea what to do about this ,I was wondering if yall could help me out
    Joe galloway
    Ps is there another way that I can post or send anyone a photo it want let me on here

  • Debbie

    We just planted our knock out rose bush about a week ago. We have warm days and cool evenings right now. The roses look good but the leaves are turning a whitish color? We are afraid it may die. Any suggestions, please? Thanks.

  • Sheila

    My knock out roses have white on the leaves. Any idea what this is?

  • Sheila

    Knockout roses have white on leaves. Any idea what is causing this?

  • Charlet Estes

    Can pest control chemicals kill a knockout? I have one planted near my bird bath and I was having trouble with yellowjackets. My son sprayed the ground under the bush to try and ward them off. A day later, all of the blooms had dried up on the bush and now, a week later, the leaves are turning yellow and dropping. We had a bad, bad heat wave that week and I assumed it needed water, but I’ve been faithfully watering it and it’s getting worse. Now I’m afraid it was the wasp spray?

    • Amanda

      The wasp spray could definitely affect the growth of your Knock Out Rose bush, but it could also be due to too much water. Try letting the soil dry out a bit in between waterings. Check it by sticking your finger down in the soil. If it’s still moist about 2 inches below the soil line, it doesn’t need water. Fortunately, Knock Out Roses are very resilient!

      • Charlet Estes

        thank you! I’ve trimmed off all of the affected leaves and branches and thrown them away, then I sprayed it with fungicide and put some lime in the soil under it. There is a bird bath next to it, I wonder if I should move the bird bath?

  • Charlet Estes


  • Ernie

    I have lots of double knockout roses but in last yr or so were infected by the disease called Witches Broom. Now they all dwarfed and blooms have shrunk tremendously. The new shoots are all redish and soft with lots of soft thorns. Pretty much affected all my roses. Is there a solution to this?