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I bought two miniature roses last year from the same source and thought I was fighting powdery mildew. I thought they would come out of the shed and we would have a fresh start this year.

I have been growing roses for 10 years and having watched my mom try to raise them as a child I knew to have a spraying regimen for black leaf and I have always done it faithfully starting with the first leaves of the year weekly. I never had powdery mildew because of this. I couldn't figure out why it wasn't going away on the two new ones.

This spring I began to suspect downy mildew. I have a very small yard but keep "everybody" reasonably separated. I recently read that once downy mildew gets to the roots you can't get rid of it. This morning I woke up and my beautiful Medallion Tea Rose looked like somebody threw oil on the top third of it, stems and all. I am devastated. I panicked and cut it off to the ground. I just wanted that mess away from my Mr. Lincolns which are about 6 foot away and not showing any signs yet. It has been very wet this spring here. The best spray I could find locally has Malathion in it and I just got in from spraying everybody. I have 2 large climbing roses, 3 Mr. Lincoln Tea Roses, a floribunda, 2 shrub roses and 4 miniatures now that I got rid of the 2 infected ones this morning. I am beside myself and feel as though I have killed a friend. I believe after more reading I should not have taken such a drastic step with my poor Medallion.

Is Malathion a decent spray? I bough Bonide Fruit Tree Spray. Do you think all my roses are doomed? I don't want to keep any that are going to perpetually harbor downy mildew. I am sure of the original source. Nobody in my neighborhood has roses besides me. My miniatures all wintered in the same shed but they were not touching.

How long does it take for it to show when a plant is infected? I guess I just need to talk to somebody who has been through this. Thanks for listening!

Hi

Mildew and blackspot on roses are a fact of life if you live in a humid climate.

For me, it is better to select roses that have glossy leaves, they just resist mildew better.

If not, prevention is key.

I actually have more problems with black spot than mildew because my plants are well spaced and I use a drip irrigation watering system.

If I know it is the rainy season and the weather is still cool with days where the highs do not exceed 80 degrees. I will use a summer oil spray on the roses every week while the weather is extra humid.

The oil spray helps the leaves to shed water.

But, if I did not start spraying in time and it has already rained or if the daily high temps are already in the 80's, I have a back up plan.

I discovered if I spray within 3 days of rain, I can kill any fungal spores before they get a foothold. If I have not used oil within the last two weeks, I can still use sulfur spray.

I can also use a baking soda spray to help dry the leaves even if I do use an oil spray. This is especially helpful when it has been raining for days or the breezes stop and the air is especially humid.

Black spot is more of a problem. Some of my new roses, Robert Strauss, in particular is especially prone to black spot. For that I use Bayer tree and shrub or Systemic Rose control. I try to limit the systemics as a last resort because they are very harmful to bees.

Once the weather gets drier, then I use the baking soda spray to control spider mites, the fungal diseases are less of a problem.

Below is a link to the American Rose society about treatiing powdery mildew.

https://www.ars.org/?page_id=3206

I think Hawaii would be such a lovely place to live I would deal with the humidity! I use an Ortho rose disease spray weekly and it handles the black leaf and powdery mildew great. I am afraid I am up against Downy Mildew and it is a whole new ballgame for me. I have been nervous because I had the two miniatures that just haven't been right and I was starting to worry about the possibility they were harboring downy mildew and I am pretty sure I was right. From what I have read if left untreated it will travel to the roots and you can not get rid of it. I am very depressed. I moved here 5 years ago and have been nurturing most of these roses that long. They were just really getting nice. The Medallion was on track to hit 6 ft this year.
I sprayed with a spray containing Malathion this afternoon. It has a petroleum base to repel water. It was the only thing I could get local and fast that was listed to help control downy mildew. All the good solutions for it seem to be packaged in bulk and be very expensive. I am just afraid of nursing them along and having a perpetually sick plant that is a risk to the others.
My pictures are to big to attach. I will try to add one later.
Thanks for responding!

I'm sorry you're experiencing trouble with your roses and downy mildew. This article on downy mildew in impatiens discusses the spread of more invidious strains of downy mildew into common garden plants in both Europe and North America in recent years.

Because your location isn't shown in your profile, it's impossible to tell whether you're within the "impatiens affected" area of North America or not, but that particular variant of downy mildew seems to be transferred by every possible vector (I'm trying to pin down the science journal I read it in; DH brings home one from his work, and two or three are delivered to the house, plus the printouts he brings home): wind, rain, human hands touching plants, flying insects, birds.

I only scanned the linked article, and I didn't read the Michigan State University article it references at all. Maybe there are some recommendations there on roses?

We're gardening in "interesting times," unfortunately, it seems.

Cynthia H.
Sunset Zone 17, USDA Zone 9

Downy mildew is a much more virulent disease than powdery mildew. Plants can frequently live with powdery mildew for a pretty long time, not so the downy mildew which seems to be a relatively new scourge.

Here's an article about downy mildew on roses:

https://www.ars.org/?page_id=3197

The best course seems to be prevention. If you spray your roses with an anti-fungal every week or two or after a rain, you should hopefully be able to prevent the disease. The anti-fungals I might use would be baking soda solution, hydrogen peroxide, diluted milk, compost tea, and I think it helps to rotate them, not stick with one, so the organism can't adapt.

But unfortunately prevention is easier than cure. If the downy mildew is well established on a plant, your only choice might be to sacrifice that plant, to keep all the plants of the same kind from getting wiped out. The only piece of good news here is that each species of downy mildew only attacks one or a few kinds of plants. Thus the downy mildew that is attacking your roses won't attack other kinds of plants in your garden.

Everyone has to make their own choices. But if you are going to end up sacrificing your plants anyway, it seems a shame to be spreading malathion around. It is a broad spectrum poison that spreads through air and water and is quite toxic to fish, amphibians, birds, butterflies, honeybees and probably somewhat toxic to humans and pets.

I live in Kansas City Missouri. We have our share of humidity here normally but this year has been unusually wet.
I try not to use an excess of chemicals although I must confess to spraying for black leaf once a week with Ortho. It is the only way I have found to control it over the long term in this area. I have a dog that is critically allergic to weed spray, insect spray, laundry soap, and pretty much everything under the sun and try to keep such things to a minimum.
I will figure out how to reduce the size of my pictures and post some this afternoon.
Thanks for responding.