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Tennessee Gardening

Help with Knockout Roses

9 years ago

I have lost 4 mature Knockout Roses, about 10 years old. They will start by having one branch die, I will prune that branch, and then another will die, this continues until the entire plant is dead. I still have 11 left and don't want to lose those. 3 of the plants were in one part of the bed and the last was in a group of 10 plants. I find no evidence of living pests on the plants. Has any one else had this problem? Any suggestions as to the cause?

Featured Answer

stillanntn6b

9 years ago

Rose Rosette has been a major problem in many mass plantings of KnockOuts AND other roses throughout Tennessee. You won't see the mites that vector the disease unless you use a hand lens that allows 20x magnification.

This spring, when growth begins, if you'll post pictures, a diagnosis may be fairly easy. I do have a lot of experience with RRD.

In the meantime, you may want to read a few chapters of my Rose Rosette E-book which does have a large bibliography of papers about the disease. And lots of pictures. Rose Rosette e-book

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Comments (8)

brandon7 TN_zone7
9 years ago
Without more information, it will be hard to determine, for sure, what's going on. A picture or two might really help. Just to "throw a dart while blindfolded", I'll recommend you Google 'rose rosette diseases" and see if the symptoms might look familiar.
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User
9 years ago
I lost a 4 year old last year, same sort of decline. I did a search and think it was a bug, possibly thrips from similar photos of infestations.

I dug the dead one out and left that area alone for 6 months. I transplanted 3 roses and added a pink knock out. Just recently I treated all my roses and indian hawthorn which was really showing insect damage. i originally started this search because of the hawthorn looking ill. That led me to rosé pictures and well, I had a match.

I couldn't see any bugs even with my magnifier.

So far, so good. Fingers crossed though!

Don't forget your local extension office as a resource in figuring out what's going on.
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It would help a great deal if we knew where you lived and what kind of weather conditions you've been experiencing. If the cane is still green where those leaves have dried up you do not need to cut the can off. The leaves will replace themselves once the problem is solved. If the canes themselves are turning brown or black then they need to be removed down to good green cane. Do examine the plant carefully to see if there are any insects on it or any damage to the canes. Dig below the surface and see what's going on down there. Is it bone dry or swampy? Either of those could cause die back. Hold the canes at the top and try and rock the plant back and forth. If it moves easily and freely there could indeed be something eating the roots. Come back with more info on what you find and maybe we can get more specific with our help.
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I lost about 30 roses to RRD here in Blanchard. A friend in Edmond lost upward of 100 plants. I agree that you should watch and wait. If you see the classic "witches broom" growth you'll know for sure. Here's a link to a good photo. Because I had so many affected I was brutal in my killing, as was my Edmond friend. We both had all varieties of roses affected. We had huge collections from Heirloom Roses in Oregon, but the virus came from a few plants bought in Edmond and spread by the mites.http://nicolewarduk.blogspot.com/2012/04/disease-resistant-knockout-rose.html
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That's what mine do, yeah! Just some roses, not all of them, but there end up being too many to squish, because some of the roses are quite tall, too! I do use spinosad. Once. When the bees are all in for the night. I do just squish them when they aren't quite so rampant :) Edit - Oh, I do leave enough on my other roses that predators are happy. I have all kinds of birds and wasps in my yard, and toads, too. They just don't choose to pick off every rose slug, either, for whatever reason. They have better things to eat here, apparently, lol :D
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They are in bad shape but I believe they can be salvaged. I like to water my roses often but I let the soil dry out in between waterings (they like a drink, but don't like to swim). I feed them every once in a while all depending on how they are growing. Whatever fertilizer you use, make sure you follow the dosages printed on the label. If you want to fertilize more often then use a weaker dose. There is such a thing as too much food. After these bushes leaf out I would give them a haircut. There is no telling how much abuse they put up with before you got them. If the roots are healthy and the plant is strong then I would cut all the branches back by half now but if they were starved for attention and are not in good health then I would wait and let this new crop of leaves boost the plants energy for the rest of this season and then cut them way back after your first freeze. To keep them in tip top shape you will have to learn how to prune them and keep them on a feeding schedule.
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neil64
Original Author
9 years ago
Thanks for the advice. I have contacted the Extension office, no help. New young agent.
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brandon7 TN_zone7
9 years ago
This forum has some seasoned rosarians, so if you can supply the data (information, pictures), I think there's a good chance someone can give you an answer. Also, there are multiple rose-related forums on GardenWeb. They'll have to have more info too, though.
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Jessica Rieman
9 years ago
We lost more than 20 double knock-outs to Rose Rosette. So sad! I wonder how long until we can bring in roses again? The old ones have been completely removed & burned.
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Kitchenlady (Tennessee, Zone 7a)
8 years ago
Just looking through some of these old posts and wanted to say thanks for the info on rose rosette. I had no idea what was happening to one of my knockout roses, but this is definitely it! Did I read correctly that I need to completely remove the rose bush and destroy it? :( What a bummer.

I've got 3 knockout roses fairly close together near my mailbox in full sun... only one of them got the strange witches brooms.
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stillanntn6b
8 years ago
Do dig it up and try to get all of its roots out.
Then watch the other roses and if you see odd growth on them cut the odd off at least eight inches below the odd part.

Ann
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