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Double Knock Out Roses: Avoid the Common Diseases

Double Knock Out Roses: Avoid the Common Diseases

So, you’ve fallen in love with Double Knock Out Roses. But how do you prevent disease?

What’s not to love? Double Knock Out Roses have so many benefits and bigger, better blooms than traditional roses!

But chances are that, whether you are considering the purchase of a Knock Out 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 Knock Outs be affected by the same plights?

Double Knock Out 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 Knock Out Roses can still get hit by some diseases.

Let’s take a moment to learn about the five most common diseases that a Knock Out 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 Knock Out Roses in Bloom
Blooming Beauties

Named 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 Knock Out from reaching its maximum height and causes the affected leaves to become dry and eventually fall off.

Stem Canker
Rich Blooms on Classic Knock Out Roses
Keep Knock Outs Healthy

Stem 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.


Double Knock Out Roses

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, Knock Out Roses are hardier than other varieties. So while these five diseases can happen, your Knock Out is far less susceptible to them than other varieties may be.

You can ensure that your rose does not succumb to disease with 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 (in case of temperature or drought), take care to do so only at the soil level.


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

Remember, when it comes to Knock Out Roses, an ounce of prevention is better (and easier!) than any cure.

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