Diseases of knockout roses

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.

My Knock Out Rose Bush Is Dying

Jupiterimages/Photos.com/Getty Images

All roses, even the beautiful and hardy Knock Out, can sometimes have problems. While most of these issues will not kill the plant, they can cause leaf spots, yellowing, wilting and blight that may make it look like the rose is dying.

Pests and Disease

Black spot disease and mildew can still cause problems for Knock Out roses. In addition, pests like aphids, sawfly larvae and spider mites will often feed on Knock Outs. If left unchecked, these diseases and pests can weaken the plant and make it susceptible to disease and extremes of cold and heat.

Hydration

Roses do not like to have wet feet but still need adequate water. A good rule of thumb is to water 1 inch per week, 2 inches in arid climates or drought conditions. Mulch around the base of the rose to hold moisture.

Pruning

Knock Out roses should be pruned hard in the spring. Remove all crossing tips and branches, and thin the rose to provide adequate airflow.

Hardiness Zone Issues

Knock Out roses are considered to be hardy through U.S. Department of Agriculture Zone 5, but if you live in an area close to the dividing line between two zones, your roses may not tolerate harsher weather. Consider replacing your Knock Out with a rose more suited for your location.

Knock Out Roses are actually considered a shrub and not a flower. They are used as borders and when placed in groupings they make an amazing focal point. We have them as a border down our driveway and in groupings in our backyard. When these are in bloom the view driving into the house is spectacular!

Knockout Roses started becoming popular around 2000 and they were the best selling landscaping plant that year in the entire country! People loved the fullness of the shrub with the full blooms. They also had a reputation for low care level,

Considered immune to disease and self dead heading, knock out roses bloom every five weeks. They bloom continuously throughout the summer and their blooms last for a few weeks.

We have them in the driveway I mentioned, and also a few groupings in the backyard so I have a lot of experience seeing these plants grow.

caring for knockout Roses

Despite that they were considered very low maintenance and free from disease, I have had a few plants be taken over by disease. While I do not spray any of my knock out roses, I have lost a few along the way. Having said this, I probably have at least 2.5 dozen of these plants and have really only lost 4 or so, so the odds are in your favor if you plant these gorgeous shrubs!

While a lot of people say they dead head or “self clean” themselves, I prefer to keep up with the dead heading. But then again, in the summer I walk around with pruning shears and clean everything up constantly so that just be my need to clip something! We have landscapers who trim them back down after the blooms are wilting but that’s because I’m trying to keep mine at a a certain height. If left to grow these bushes will get bigger and bigger! I do remember once that we were having a party and while the roses weren’t in perfect shape, they still had great color. When I walked outside and our landscaper had taken every single bloom off! I was like “NO! There goes my beautiful entry for the party!” Ha. Such problems in life, right?

If you’re going to plant these, plant the knockout roses in early spring or late fall. Don’t bother planting these mid-summer. In my experience they won’t take. They also need 4-6 hours of direct sun.

But with spring upon us soon, now would be a perfect time to start eyeing where you could put some of these beauties.

Knock out roses come in four colors, though I’ve only seen two of these in the Atlanta area. Red and pink (which is what I mainly see) and yellow and white. Here’s a nice link to show the colors. They are gorgeous!

I find that these flowers are sweet little flowers to put in a tiny bud vase for my daughter. The stems are very prickly and not quite long enough to use in flower arrangements though. But a sweet little clipping in a tiny bud vase is really cute. I love to surprise my daughter with some on her nightstand!

I’ve grown roses for years….

tea roses, climbing roses, gradiflora, etc… etc… but I must confess something,

when it comes to roses,

I’ve killed more roses than I’d like to admit.

GASP!!! Hey, no one is perfect!

Yes, my thumbs aren’t always green…. their usually covered in blackspot…

dang blackspot… you are the thorn in my side…errr…rose!

Because I live in the south where the sun is hot, hot, hot, and humidity is thick as a men’s steam room…. (yuck, sorry for that visual),

I want roses, what girl doesn’t love roses?

…but roses that aren’t high maintenance!

No DIVA ROSES ALLOWED in my yard!

I want roses that any brown thumb gardener can grow.

I want EASY ROSES!

And I’m happy to tell you that I have found them! They are Knock Out Roses. They are almost indestructible. Woo-hoo!

Look at this gorgeous hedge of roses dividing my yard from my neighbors. I planted them 3 years ago. Our soil sucks. I’m talking clay soil. So much clay you could sculpt a clay pot with them! All I did was dig a hole 2x the size of the pot they came in, set the plant in the hole, backfilled with good quality top soil and then added 1/2 cup of rose food to the surrounding soil. That is it!

Knock Out Roses will quickly grow to 4ft x 4ft. They resist blackspot (yay), do not need dead-heading (unless you desire it), and the best part….

THEY BLOOM FROM SPRING UNTIL THE FIRST FROST!

What else do you have in your garden that can say that?

The picture below is year 2 of Knockout Roses planted on either side of my entrance. (Basically they double in size each year).

This variety is the original Knockout Rose in red.

The fun option is to have DOUBLE KnockOut Roses. This variety produced very full flowers and mimics the look of an open tea rose, which is very appealing.

Features:

drought tolerant

disease/pest/blackspot resistant

double blooms

darkgreen/purple foliage

blooms spring-1st frost

zones 5-11

This lovely variety below is The Pink Double Knockout Rose.

Features:

low maintenance

tons of flowers/ repeat bloomer

drought tolerant

disease/pest/ black spot resistant

3-4′ tall/wide

double blooms- spring -1st frost

Zones 5-11

I would love to add this beauty to my garden. This is the Rainbow Knockout Rose.

It boasts coral pink blooms with bright yellow centers and is more compact than the other varieties. It rarely ever has any issues with blackspot which is a must-have if you live in humid regions.

Features:

Very Blackspot resistant

drought tolerant

tons of flowers

3-4 feet

foliage- deep burgundy aging to deep green.

Zones 5-11

Add a touch of sunshine to your garden with the Sunny Knockout Rose.

This rose is the newest in the Knockout collection. It is the one variety that has a strong fragrance. It is more upright and compact than the other varieties. The blooms start off as bright yellow then quickly fade to a pale, creamy yellow. During cooler times of the year, the blossoms will be more vibrant in color. If you’ve ever tried to grow yellow roses in the south, then you KNOW how difficult they can be! This plant provides worry free blooms all season!

Features:

3-5 feet tall (largest of the group)

low maintenance

drought/ blackspot/disease/pest resistant

Repeat bloomer

tons of flowers

slight-strong fragrance

zone 5-11

last 4 pics via Conrad-Pyle

If you consider yourself a brown thumb gardener then PLEASE buy these Knockout Roses.

Now look, EVERY plant needs water. These are not cacti! You do need to water them once a week if you are in hot climates like mine (I’m in zone 8). And these roses do need at LEAST 6 hours of sunshine each day. I have Knockouts on the very hot and sunny south side of my home and on the shadier north side of my home. They both are doing well, but the sunnier south side have grown fuller and bloom better. They all have thorns but you will have a house FILLED with rose bloom cuttings all spring, summer, and fall!

I only fertilize each rose bush one time a year in spring with 1/2 cup of granulated rose food. That’s it.

These babies are love ’em & leave ’em!

If you are even capable of killing Knockouts then you deserve some type of brown thumb award, because I’m telling you,

YOU CAN’T GO WRONG WITH KNOCKOUT ROSES!

Let me know if you have any questions and I’ll try to answer them asap.

Happy Gardening!

For more gardening tips & tricks, check out my GARDENING tab up at the top of the blog.

Kim

Knock Out rose down for the count

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Finally, our plants are revealing the ravages of our most brutal winter.

In my yard, the Knock Out red rose (Rosa ‘Radrazz’) has died, which frankly, is all right with me. I was getting bored with it and tired of seeing it planted in every gas station, restaurant and strip mall in the country. Hardy to USDA Zone 5 (minus 20 degrees), our series of record cold blasts likely did this plant in, so it’s coming out.

If there are leaves or green branches emerging from the bottom of your Knock Out, cut the shrub back to the new growth. This fast-growing rose will likely bloom again this summer.

I thought for sure that I’d lost the five variegated Solomon’s seals (Polygonatum odoratum ‘Variegatum’) that I had planted last summer. These were the Perennial Plant of the Year in 2013. I’d even told people I’d lost them, but there they are, the nice clump I planted, just a bit slower to emerge than expected. Another one of those “gardening teaches us patience” moments.

Little Henry Virginia sweetspire (Itea virginica ‘Sprich’) also has not leafed out. It looks like there’s one branch that’s green, but this shrub has not thrived in my landscape, so I’m pulling it out. This cultivar of a native plant is hardy to USDA Zone 5.

Gardeners are reporting the browning of arborvitae shrubs (Thuju), broadleaf hollies (Ilex), the yellowing of Eastern white pine (Pinus strobus) and few to no leaves on azaleas and rhododendrons (Rhododendron). Brown leaves on evergreens will not green up. If the damage is patchy, you can prune out the brown branches. If the browning is extensive, replace the plant.

The one miracle in my landscape is the ever-so-slow, but promising emergence of the delicate maidenhair fern (Adiantum pendatum). This lovely, and a bit hard to find, native fern is hardy to USDA Zone 3 (minus 40 degrees). This one is special because a customer at the garden center where I work dug up part of her clump to share.

Still to be revealed: Winter’s effect on insect populations.

Jo Ellen Meyers Sharp (http://hoosiergardener.com) is secretary of Garden Writers Association and co-author of “The Indiana Gardener’s Guide.” Write to her at P.O. Box 20310, Indianapolis, IN 46220-0310, or email [email protected]

© The Hoosier Gardener

Rose Rosette Disease. What To Do When You Get It.

My plant of Flamenco Rosita that got infected and had to be removed. I replaced it with another.
Photo/Illustration: Paul Zimmerman Roses

Welcome to our third and final post in our series on Rose Rosette Disease (RRD). In our first post we talked about the history of RRD and addressed the rumor that The Knock Out Roses are to blame – something totally untrue. In our second post we talked about steps you can take to prevent it from occurring. In this post we are going to talk about what you can do if you get it.

Sadly, very little.

There is no “cure” for RRD that you can use to treat a rose once it’s infected. However, if you act quickly you might, just might, be able to save the rose. To understand why this might work it’s important to understand what happens once RRD infects the plant.

The mite that transmits RRD prefers the softer, young foliage found on top of the plant. This is generally where you will see the first signs of the disease. For whatever reason it seems to start by infecting only one cane – leaving the other canes unaffected. This is the first key.

The second key is to understand that RRD appears to travel very slowly through the plant. Therefore, if only one cane is infected it means the disease has to travel through the plant from the top of that cane, to the base of the plant and then up to the rest of the plant. It won’t jump from leaf to leaf unless the mites do.

Using this knowledge I’ve been about 50% successful in saving plants infected with RRD. The method to do so is quite radical and you can’t be shy or do it halfway.

If you see RRD on the top of a cane follow that cane to the ground and cut it out completely. Don’t hesitate and don’t over think it. Just do it!

If you were able to act quickly enough you removed the infected cane before RRD got into the base of the plant and traveled up into the rest of it. Be aware, it could be a year before you know if you succeeded so be vigilant. Hopefully, however, you got it in time and that’s that.

Which brings us to the question, what if you didn’t get it in time and it does spread to the rest of the plant. In this case there is only one thing you can do.

Grab a shovel and dig out the entire bush roots and all.

Get every bit of plant you can and especially the roots. Any new rose planted in that spot may intertwine with infected roots of the old plant and get RRD. It pays to be thorough in this case.

A few more things I want to say about RRD before we close this series off.

First, those of you who have read my writings know I sometimes make fun of the “rule” of dipping your pruners in bleach between cuts when pruning. I do think that is silly but of course there is an exception to every rule and this is one of those. When cutting, or working, on roses with RRD sanitize your tools in bleach when you are done.

Secondly, I’d like to pass along an experiment someone I know is doing. Instead of cutting out just the cane on infected roses, they are also cutting out a section of the bud union or base of the plant the cane was attached to. This apparently an old arborist trick and it will simply heal over. He’s tried it with several roses and so far they are staying clean. We have no idea if this will work all the time but if you get an infected rose and are willing to try it, send us the results.

RRD is no fun. I should know as I just tore out my mature Flamenco Rosita plant, leaving a huge hole in my garden. While, I’m not happy about that, I also know there are other things that can kill plants besides RRD. I’m just going to be vigilant and deal with it when it comes. And if I do have to dig out a rose there is only one way to react.

Go rose shopping!

Happy Roseing
Paul

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Rose Rosette Disease

The question begins, “Neil, my rose is behaving strangely. It has strong bull canes that are absolutely covered with thorns. Other canes appear normal. However, the buds never open properly, and the plant seems to be stunted and losing ground. What could the problem be?”

Rose rosette disease (“RRD”) is not new. In fact, it’s been known to exist for decades. However, for whatever the reasons, it has proliferated in DFW and elsewhere in Texas over the past several years. Tens of thousands of roses have been afflicted, and at present there seems to be no prevention or remedy for it.

What we know:

  • RRD causes erratic growth of affected plants.
  • Canes are malformed, almost as if a broadleafed weedkiller might have drifted onto the plants.
  • Affected canes are coated with hundreds of aggressive thorns – several times the normal number.

  • Other canes will appear normal, BUT the entire plant is infected if any part of it is.

  • The disease is spread by microscopic mites that are easily transferred from plant to plant and yard to yard. The mites are even carried by the wind. You will not be able to see the mites.
  • There is no prevention or cure for RRD. Pruning to remove the obviously infected canes alone will not help. Remember: the entire plant is infected if any part of it is.
  • You will see references to home remedies. These do not work, and they serve only to allow the disease to spread while the gardener is trying futilely to save existing plants.
  • As soon as you identify RRD in your garden, you should remove all affected plants, roots and all. Carefully place them in large plastic trash bags and send them out with the trash. Do not try to shred and compost them.

What we do not know:

  • How long you must wait before planting new roses back into the same soil? I hear varying recommendations from within a couple of weeks to one or two years. Honestly, if this were attacking my roses, I’d put any new rose plantings in fresh soil somewhere else in my garden, at least for now.
  • Specifically, which varieties are vulnerable? Certainly the Knock Out® family has been hit the worst, but that’s probably since they have been planted so extensively, often in masses in large beds. Other roses are also susceptible. Research is underway to determine which types are most and least likely to develop the problem.
  • Where will we find a remedy? Breeders, I am told, are working with the genetics of their roses, even to the level of work within laboratories, to find resistance. I’m not an expert in this field, but I have heard no mention of a consumer miticide to control the mites. Honestly, I’m not sure anyone knows where we will find help for our roses, but the nursery industry has invested millions of dollars into the research projects.

If you think you may have infected plants

  • Take photographs and compare them to the ones you see here. Once you have seen RRD (as in these photographs), you will know how to recognize it (click thumbnails to view larger images).
  • Take photographs to a Texas Master Certified Nursery Professional for help in confirming presence of the disease. DO NOT take actual plant samples into nurseries. If you do have RRD on your roses, don’t take the chance of spreading it to healthy nursery stock.
  • Immediately upon confirmation of the disease, remove all affected plants as described above.

What information is available online?

A Facebook friend shared this really helpful and academically-driven compendium of information. I think you’ll find it useful. https://roserosette.org

What can be planted to replace the roses?

Without wanting to sound like I’m avoiding the question, I do have to say that roses are unique plants. No replacement shrubs or vines will be exact replacements. It’s important to note that RRD afflicts only roses. You don’t have to worry about other types of plants picking up the disease.

If you’re looking for the best low to mid-sized shrubs, consider the various types of dwarf hollies, nandinas, dwarf abelias, low junipers and other woody plants that are adapted to your part of Texas. Your local independent nursery can fine-tune your options.

Perennials are another good choice, especially if you’re seeking color in the old rose bed. You have scores of types from which to choose. Choose varieties that will give you a nice succession of blooms. Be mindful of their flowering times, mature heights and colors. It’s wise to plant a few evergreen woody plants to anchor the bed visually during the winter dormant season.

Annuals are quick and easy. They’re also affordable, and most will be colorful for five or six months each summer. Determine what height you want them to grow and what colors you want, then let your nursery professional suggest some of the best. As with perennials, the bed will look better if you anchor it with a few evergreen shrubs.

Support information

I have accumulated several good pieces of information pertinent to RRD. A couple of these are several years old, but what they say is still highly relevant.

From the Virginia Cooperative Extension:

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