Black Spot Stems on Knockouts

Chicago, IL(Zone 5b)

I have two double pink knockout shrub roses and both are presenting with what I assume to be black spot on the stems. I also see a few stems with cane borer damage. I got a good look at them when I was pruning them yesterday. Should I prune all the diseased stems back to the ground? From the looks of it, there won't be much rose left once I get to whacking. Should I just trash it?

FWIW, the shrubs looked great and flowered all summer last year. I also fertilize with the Bayer All In One Rose Care on a regular schedule.

All comments and advice would be greatly appreciated.

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Richmond, TX

KnockOuts are tough. I would just wait and see what happens when they leaf out. There is a good chance they will be as vigorous as last year again.

Your garden is quite lovely in that last photo!

Chicago, IL(Zone 5b)

Hi porkpal, after being locked up in the house all winter I have an itchy pruning finger! I hate seeing so many damaged stems and trying hard to resist the urge to cut it all away. I don't have much knowledge with proper pruning technique so I'll just do as you say and chill till they leaf out. Thank you for complimenting my garden, the long and hot summer was unusual for Chicago but it made some of the plants grow like I've never seen before in this zone.

Grosse Pointe Shores, MI(Zone 6a)

Mine look the same way...I'm a bit concerned about them.

Bellmead, TX(Zone 8b)

If it were here in Texas I would say take them back down to about 5 inches from the crown. They would healthier and produce more roses next season, but I am not sure when your roses go dormant for the winter. If you have a good three or four months before the next cold snap I would say prune them.

Knock outs are hardy but they can get really leggy and they do tend to need their care changed up a bit from time to time. I would add some egg and coffee grounds to the soil directly under the plants. This will help the stems to grow stronger naturally. You might have to let the soil dry out some between waterings too. Sometimes blackspot is caused by the water that is below the plant (not on the surface where you can see.) If you want to know for sure, dig a little section under the plant about 3 or 4 inches out and see how moist the soil is when you get to the roots.

My other suggestion is stop using the fertilizer for a bit and switch to simply aspirin dissolved in water. I believe the ratio is 3-325 mg aspirin tablets per 4 gal water plus a TBSP of soap as fixative. Aspirin sprayed roses have larger new leaves, bigger canes & more blooms.

Just a thought. Sent you a pic of some of my Knock Outs from a house we sold last year. Miss them so much!

Angel - Hi by the way :)

This message was edited Apr 1, 2013 12:17 PM

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Bellmead, TX(Zone 8b)

Opps pictures didn't come through here they are.


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Chicago, IL(Zone 5b)

Hi koshki, sorry to hear you're experiencing the same problem. I noticed only the pink KO have the blackspot stems. I have one red KO and it's fine. On the positive side, they are beginning to bud so I guess they're not totally gone. Now we just need some warmer weather. :)

Chicago, IL(Zone 5b)

Hi Angel, I have already pruned them by about 1/3 so would really hate to lose the height and start from ground again, but if need be, the diseased stems will be removed. These roses are 4 years old and performed best in year 2. Last summer was really hot and dry so the blackspot on the leaves was surprising to me b/c I always water the roses at the base trying not to get the leaves wet.

As far as fertilizer, egg shells I can do since I boil a dozen each week for work but the coffee grounds are no more (can't drink the amount of coffee like I used to). I'll wait and see how they leaf out and then reassess the situation. Hopefully, they come to their senses b/c I don't feel like fussing over supposedly "fuss-free" rosebushes.

I love the red KO's you had. The one red I have is such a vibrant color; wish I would have bought the double reds instead of the pink. I tend to like plants with dark or burgundy-like foliage.

Bellmead, TX(Zone 8b)


Thanks for the compliment. I had some pink primrose ko's as well that my neighbor manage to all but kill. They dug them up and were going to throw them out and at the last minute asked if I wanted to see if I could revive them. I did and they almost asked for them back - but they were mine! LOL

I would just watch your beauties to make sure they don't get too leggy. They tend to throw out buds from the top and the "damaged" stalks are bare. If that happens you will need to prune them back in the fall for sure.

Instead of coffee grounds, use banana peels then. You can either bury them just below the surface or just throw them under the mulch at the base of your roses. Keep us posted on their progress!


Richmond, TX

I hear Starbucks will give you coffee grounds free.

Marshalltown, IA(Zone 5a)


Here in zone 5, my second year with the KO's did the same thing....I was new to roses, and the first year, they did get some black spot...and I sprayed....but still lost some leaves...then, in the following spring, mine did the same as looked like black spot on the, I trimmed them back to about 6-8m inches, and cleaned the dirt area really well....then in the early spring, I fertilized them and they turned out beautiful ....

So, I thing the pruning and fertilizing will work out fine.....

West Monroe, LA(Zone 8a)

Can't help with advice, too far south here. But, I just love the garden surrounding your rose.

Southeastern, NH(Zone 5b)

My roses always have some black spots on them in spring. I think it is mostly cold damage more than anything. I just prune them the way I always do, which is leave about 12" of the healthy stems and remove the oldest unhealthiest looking right down as close to the ground as possible. I also make sure to make them have a vase like shape and remove any branches that cross through the middle. I don't have any knockouts but I do have a variety and this method works well on all. They usually put out tons of new growth anyway. I also use the Bayer product you mentioned. :) I would continue using it if I were you. The main reason I use it is for the disease prevention. I also use an organic rose fertilizer. Rose Tone to be exact.

This message was edited Apr 25, 2013 8:43 PM

Austin, TX

Black spot is normally a fungal disease caused by an opportunistic fungus that grows in moist conditions. The best way to avoid it is to keep the plants dry. Water the soil, not the foliage. It's OK to get the foliage wet if its warm and windy and will dry off quickly.

It seems many people who have black spot on roses use an automated sprinkler system. If you live in an area that gets a lot of rain, your plants will be more susceptible.

Greenville, SC(Zone 7a)

Mine had a similar problem this year ( We had a lot more rain this year then usual) Cut some back and it just filled in from there, Here is a photo from the other day ..

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Richmond, TX

Iris, that bush certainly looks healthy!

Toni, how are yours doing?

Greenville, SC(Zone 7a)

porkpal, thanks, I have two the same size right by each other and they are both bloomed out, But, i have a climbing Don Juan Rose thats not doing so well, Did Great last year, This year the leaves keep turning and falling off!! Lots of blooms, But, I don't understand at all why the leaves are falling off ... Going to have to post about it later and see if maybe someone would know...

Richmond, TX

I have a number of roses, including Don Juan, that lose all their leaves repeatedly - usually to black spot - but they somehow keep blooming...?

Easton, PA(Zone 6b)

I have some canes with the same problem on a couple of roses. If the rose has lots of canes, I cut the diseased cane down to the ground. If not, I cut below the diseased section. Most of my roses are won root like the knockouts.

I seal all cuts with glue - Elmers is fine, even the one from the dollar store. I saw a borer this year on a cut end of one of my dark stemmed roses. Yikes. Nasty creature.

Thanks for the tip on the aspirin. I never heard that one before!

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