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knockout rose problem

Posted by lowellches 8/9 N Florida (My Page) on
Tue, Jun 24, 14 at 15:02

My Knockout Roses: have flourished for several years. But not this year.
I prune the bushes back substantially each year during the winter, usually in February. This year I pruned them back further. It took longer for them to grow out and make flowers but they seemed normal at first.
Then they lost blooms and leaves and plants looked like they were dying.
In the past few weeks they have gradually gotten some new leaf growth but minimal. They do not fully leaf out and have odd leaves. Very few blooms. There may be half a dozen blooms now on 58 bushes. There seems to be no growth of canes.

They were sprayed once with liquid Sevin brand XLR Plus. Active ingredient: carbaryl insecticide (1-naphthyl N-methylcarbamate). That was maybe 2 months ago and I thought it must have caused the damage but on the internet I see references of folks using Sevin on Knockouts.
They have been fertilized with Ozmocote and about � the plants have had Miracle Grow gardensoil placed around them, maybe 3 weeks ago. I see no apparent difference between plants with the soil vs those without.

My questions are:
What caused this ?
What can I do for them?

thank you very much

Follow-Up Postings:

RE: knockout rose problem

Herbicide damage?

RE: knockout rose problem

No expert myself. But if you post close up pictures, people on this forum might be able to help more. It could be RRD to my untrained eyes.

RE: knockout rose problem

No herbicides used.

another photo

RE: knockout rose problem

Closeups of "odd leaves" would help. The new red growth looks OK. The old foliage is too pale and yellowish for KO roses. Do the pale leaves have green veins?

Do you know whether the plants were grafted on Fortuniana rootstock, as Florida roses should be? If not, the plants could be declining because of root-knot nematodes.

Plants from western growers are on Dr. Huey rootstock, which is usually good for 2-3 years in warm sandy soils.

This post was edited by michaelg on Fri, Jun 27, 14 at 9:47

RE: knockout rose problem

It might help if you cut out everything that is black, gray, or brown--and I mean everything. All that stuff is dead. Then we can see what is left and what condition it is in.

Right off the bat I'm inclined to say it needs more water and regular watering--and patience. In another month, the new red growth should have matured into nice green growth that wants to produce buds and blooms.

If you had a brutal winter like many of us did, then your roses just need more time to recover.

But a good clear close-up of the sections that concern you would help in making a more precise diagnosis.


RE: knockout rose problem

I noticed today the same problem with my knock-outs. I think the problem with mine is that they are planted at the line with my neighbor who uses a lawn service. I suspect it is herbicide damage.

RE: knockout rose problem

Well, here is result of 2 more months of "growth". Yes, they have been watered and fertilized. Upper photo in the collage was taken in 2013. Lower 2 photos were taken today. Depressing.

Note: In July, mulch was removed due to concern of possible contamination. Also plants were sprayed with pesticide recommended by nursery. Sprayed once a week for 3 weeks. Also put Miracle grow soil around some bushes and organic compost around others. No apparent difference between any bushes. All equally sad.

BTW: is it possible to post more that 1 photo here? I hope the collage works.

RE: knockout rose problem

Please indulge my curiousity because I'm in Florida, and I don't have anything that "eats" my rose plants -flowers yes, plants no.

What was eating 'em that required an agricultural strength pesticide?
Or asked another way, why did the nursery recommend that product?

And "mulch was removed due to concern of possible contamination." Contamination with or by what?

RE: knockout rose problem

What follows are my opinions if nothing was really eating them and you didn't contaminate the flower bed.

My take on the situation: the removal of the mulch and inadequate water are the problem. The removed mulch reveals what they are planted in which looks like unimproved nearly sterile Florida sand (looking at the lower two photos of the collage). Sand like that holds NO water and needs LOTS of regular water.

Under the circumstances, I believe that they are actually doing great.

If you continue to water and put down new mulch when the high temps fall to the low 80's, then I expect they'll perk up.

Lastly, NEVER ferltilize roses in Florida in the summer. NEVER. When the summer rains take their hiatus, as they do every year, the combined heat and fertilizer stress is too much.

Now it is very likely that someone else will give you conflicting advice. If so, I recommend you take it from them.

RE: knockout rose problem

What sandandsun said makes sense to me.

The photos are so small that I really cannot make out much in them--except that it looks like you did not prune out all the deadwood as I recommended.

No, you cannot post more than one photo per post if you use the GW system. You can post again several times in a row with a different picture per each post.

Or you can upload your pics at a free service like (there are others also) and then download the HTML CODE they provide and insert it in the GW message box (here). In that case, you can insert as many pics as you want and type before and after each pic .

You also said, "Also plants were sprayed with pesticide recommended by nursery. Sprayed once a week for 3 weeks." That is a lot of spraying. What pesticide was it you used? Or do you mean fungicide? If so, what fungicide?

Like SandandSun, I think they need watering and mulching and pruning out of all the deadwood.

Numerous close-up shots of the various old and new leaves would be helpful.


RE: knockout rose problem

I would add mulch, water when the soil is almost dry (use 50% more water per watering than usual in sandy soils) and do a soil test to check for salt toxicity (too much salt) and mineral defficiencies. Then add organic compost at the recommended levels per your soil test result.

This post was edited by luis_pr on Tue, Sep 2, 14 at 8:43

RE: knockout rose problem

Never apply insecticide unless a particular pest that has serious consequences has been identified. You are stressing the plants unnecessarily with chemicals that can burn leaves. The symptom of Sevin poisoning would be bronzing and dead brown spots on the leaves. However, I doubt that is the problem.

Let me repeat my point that, if you plant Western-grown roses in Florida sand, they will decline after 2-3 years from root-knot nematodes. If you dig such a plant for inspection, the roots will be sparse and lumpy, Choose Florida-grown roses on nematode-resistant Fortuniana rootstock.

If that is not the problem, it is probably insufficient water or nutrition. In sandy soil during summer, pants need water every three days and over an inch (about 6 gallons) per week.

I strongly disagree with the advice not to fertilize in summer. When I gardened in Central Florida, we fed roses every 4-6 weeks year around. Malcolm Manners is a professor of horticulture in Lakeland and a world expert on roses. He feeds twice as much in summer as in winter because the rainy season leaches nutrients from the sandy soil. He uses Osmocote-for-Florida every 3 months plus organic ferts and lime.

Let me ask again if the yellowish leaves have green veins.

You should get a soil test through the county extension agent.

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