Common Knock Out Rose Problems: Diseases Of Knock Out Roses
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 plague 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:
- Black Spot Fungus
- Botrytis Blight (aka: Gray Mold)
- Powdery Mildew
- Rust
- Stem Canker
A well fed, well hydrated and actively growing Knock Out rose bush will be able to fend off these diseases. However, if we add into the scenario the stresses of injury (perhaps due to a weed whacker), heat stress, lack of water, poor soil, 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.
And then there's that virus mentioned earlier, a 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. 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 one that has compost and little to no fertilizers). Here is a listing of symptoms of the Rose Rosette virus:
- 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 appear to be growing in a spiral pattern.
- The 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 is far easier to manage if noticed early on. In my rose beds, I try to keep applications of pesticide to a minimum, and when I do need to make an application, I follow three simple rules:
- Positively identify the problem. There is nothing worse than using 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 before moving on to harsh chemical treatments and only if the problem is severe and nothing else helps in a reasonable amount of time.
Note: Any recommendations pertaining to the use of chemicals are for informational purposes only. Chemical control should only be used as a last resort, as organic approaches are safer and more environmentally friendly.
Gardening tips, videos, info and more delivered right to your inbox!
Sign up for the Gardening Know How newsletter today and receive a free download of our DIY eBook "Bring Your Garden Indoors: 13 DIY Projects For Fall And Winter".
Stan V. Griep contributed to Gardening Know How for many years, and has been a Colorado Native Rosarian for over four decades. He is an American Rose Society Certified Consulting Master Rosarian in the Rocky Mountain District, and a member of the Denver Rose Society, the Loveland Rose Society, and the American Rose Society. He is Gardening Know How's in-house expert on all things roses.
-
Growing Spotted Bee Balm: Find Out How To Grow Horsemint For Your Pollinator Garden
For anyone looking to cultivate native flowering plants that attract pollinators, spotted bee balm is a must! We show you how to grow horsemint for friendly garden visitors
By Tonya Barnett
-
6 Real Christmas Tree Problems To Watch Out For – And How To Fix Them Fast
Get back to enjoying the glory of your natural Christmas tree with our guide to troubleshooting common issues, from needle drop to watering woes.
By Bonnie L. Grant
-
Spindly Knockout Roses: Pruning Knockout Roses That Have Gone Leggy
Knockout roses have the reputation of being easy care plants. So, what if your knockout roses are spindly rather than full?
By Teo Spengler
-
Brown Spots On Knockout Rose Bush: Reasons For Knockout Roses Turning Brown
The knockout rose is quite beautiful, but knockouts with brown leaves can be concerning. Learn the reasons for this here.
By Tonya Barnett
-
Potted Knock Out Rose Care: How To Grow Knock Out Roses In Containers
It’s easy to understand why Knock Out roses are so popular. They’re easy care, disease resistant, and bloom all summer. Although they are often grown in the ground, container grown Knock Out roses do just as well. Learn how to grow Knock Out roses in containers here.
By Mary H. Dyer
-
Knock Out Roses Won’t Bloom – How To Get Knock Out Roses To Bloom
It is cause for major frustration when roses do not bloom in the garden. Knock Out rosebushes are no different when it comes to this frustration. There are several reasons why these roses may not bloom. This article has more information.
By Stan V. Griep
-
Yellow Knock Out Rose Leaves: What Makes Rose Leaves Turn Yellow
The yellowing of leaves on a Knock Out rose bush can mean something is not right with its health and well-being. It can also be a normal occurrence for the bush. We need to check things out to determine which signal the rose is sending us. This article will help.
By Stan V. Griep
-
Why Do My Knock Out Rose Bushes Have Rose Rosette?
There was a time when it appeared that Knock Out roses were immune to the Rose Rosette virus. However, this virus has been found in these roses for some time now. Learn more about what to do for Knock Out roses with Rose Rosette here.
By Stan V. Griep
-
How To Prune Knock Out Roses
One thing to keep in mind about Knock Out rose bushes is that they are very quick growing. A common question is "do I need to prune Knock Out roses?" Read here to look at what goes into pruning Knock Out roses.
By Stan V. Griep
-
How To Take Care Of Knock Out Roses
The Knock Out rose bush is one of the most popular roses in North America. Look at how to care for Knock Out roses in this article. Soon they will be just as popular in your garden.
By Stan V. Griep