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What's wrong with my Double Knockout roses

10 years ago

Hello everyone,

I have 2 double KOs which are around 3 years old. Every summer right after first bloom, my plants start looking terrible. I end up with holes on the leaves as if something is munching on them. Also, I get these light brown spots on them. I recently realized that one of the plants has 3 sucker canes. These sucker have grown up to the same height as the parent plant. Should I wait till fall to cut them down or can I do it now? Please let me know what's causing my leaves to brown. We had cool weather here in VA last few weeks and it's going to be in the 90s this week. Thanks a lot!

PS: Pics attached

Comments (7)

sid160
Original Author
10 years ago
Another picture. Thanks!
sid160
Original Author
10 years ago
One last picture.
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You might need a chain saw instead of a hedge trimmer. I am not kidding! Keep in mind that Knockout has some pretty lethal thorns. They can shred thick leather gloves. If you have more than a few, it can be very hard to keep up with grooming them. They are disease resistant, but they ARE NOT disease or pest free. Both regular Knockout and Double Knockout have their own charm. Double Knockout has prettier blooms, in my opinion, and they are brighter. I once had 53 regular Knockouts and currently have 3 Double Knockouts. ALL the regular Knockouts have been removed and replaced with various china and tea roses. One of my mass plantings now consists of Archduke Charles. He is wonderful, and his thorns are reasonable. He is also much more disease and pest free. I don't know if you live in an area where you can grow china roses, but it is worth checking them out. Last spring (2006) I was badly cut up from pruning Knockouts, despite wearing protection. I mean dangerously cut up. I have decided to remove the three Double Knockouts near my walkway. They are somewhat grungy looking and need to be groomed, but I do not want to get near them to take care of them because of the thorns. They also have a stiff habit of growth to them. I just need to make up my mind what to replace them with. sandy
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SW -- a photo would be very helpful, but considering it's Knockout, and considering that you're in Houston, I'll almost bet money that the problem is chili thrips. Do they have black veins and blackish stripes or spots on the stems? (see http://www.houstonrose.org/ctko1.jpg) While the Knockout series tends to be highly resistant to fungus diseases, they are extraordinarily susceptible to chili thrips. If that's the problem, you really have only three choices: 1. Replace them with a different variety. 2. Live with it and realize you're going to have a lot of dieback, regularly. Or 3. Spray for them.
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subk3
10 years ago
Sawfly larva (also called rose slugs) are dining on the undersides of the leaves. Look on the back of the leaves very carefully and you will see little tiny green caterpillar looking things. You can pick them off by hand or use an insecticidal soap like spinosad.
jim1961 / Central Pennsylvania / Zone 6
10 years ago
Yep rose slugs are munching...
Pick them off. Can be found on the underside of leaves or on the top side depending on what kind you have.
OR
Spray with safers insecticide soap after the sun goes down so leaves do not get burnt.
Same with a spinosad product.
Follow directions carefully...
sid160
Original Author
10 years ago
Any idea what's causing the brown spots?
jim1961 / Central Pennsylvania / Zone 6
10 years ago
Rose Slugs are causing some of those spotty brown/whiteish areas.
Keep the bush well watered in your heat and do not over fertilize as that also causes leaves to brown and curl.

So in the Spring when you first start seeing holes and
those spotty areas start picking those Rose Slugs off or spray safers insecticide soap/ Or spinosad before it gets worse.
You will have to repeat later on...

I grow only own root roses so I'll let someone else answer the suckering cane question...

This post was edited by jim1961 on Wed, May 29, 13 at 19:26
michaelg
10 years ago
I am not sure what the OP means by "sucker canes." A pernicious sucker on a rose is a shoot that comes from rootstock, below the graft. Unlike good shoots from the base, these will grow for months without setting a flower bud. If you have rootstock suckers, you must dig down to the point of attachment and rip the shoot out of its socket. Otherwise it will grow back.

However, it's unlikely that you would have three rootstock suckers on one plant. So maybe these are good basal shoots that will bloom soon.

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