Roses forum: Black Spot Disease on Rose Bushes

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Maryland (Zone 7a)
Mom3ubed
May 8, 2019 7:54 PM CST
Hello all! In the past 2 years since I've been here I've seen black spot disease develop on the leaves of my rose bushes. Since I know that it's highly likely to occur, is there any harm in treating them beforehand? If not, how soon can I apply the treatment? We're in zone 7 - Maryland. Thank you!
Name: Luis
Hurst, TX (Zone 8a)
Dog Lover Region: Texas
luis_pr
May 8, 2019 8:12 PM CST
Assume that the fungi is present in the stems/branches and start as soon as you see leaf out or earlier.

Or, if all this business is getting old, considerreplacing them with resistant varieties.
[Last edited by luis_pr - May 8, 2019 9:21 PM (+)]
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Name: Matt
Florida Panhandle (Zone 8b)
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MJOrwat
May 14, 2019 6:34 PM CST
Some roses need treatment for Blackspot, some don't. Climate and culture are also factors. First let's start with roses: Many hybrid teas and floribundas are succeptsble to Blackspot. Both new and older cultivars. Kordes has made some inroads recently in creating showy, and sometimes fragrant hybrid teas that are Blackspot resistant. Many old garden roses, particularly many (not all) Teas, China's, Hybrid Musks, Polyanthas, Rugosas and ramblers offer substantial resistance. Also some shrubs, such as Belinda's Dream and Knockout offer resistance. So if you decide you love a rose that is otherwise great but succeptable to BS, here are some factors to consider:
1. Blackspot occurs in wet humid climates more often than dry hot ones.
2. Keep your leaves dry. Plant your roses in areas that have good air circulation. Don't plant them too close together. Use only drip irrigation so leaves don't stay wet. Mulch so that spores don't spray from bare soil onto your plants. Pick up and remove diseased leaves.
3. Keep your roses healthy and well watered and fed. Don't skimp. Keep the pH correct. A weak rose is more disease prone.
4. Several fungicides exist to prevent Blackspot. Nothing is a perfect control. In low pressure areas Neem Oil might be sufficient. In high pressure areas such as the Gulf South (where I live) I have to spray to grow roses I love (such as Peace, Tiffany and Papa Meilland). I don't spray my Old Garden roses or shrubs, only my HTs and Floribundas. I prevent. Prevention is fairly easy and not intensive. After pruning in February I use a preventative called Lime-Sulfur. If I have canker I follow with copper 2 weeks later. In practice I try to spray (HTs only) twice a month from late March to Late October. I use a tank mix of chlorothalonil / propaconizole in cooler months and a tank mix of Mancozeb / propaconizole in warmer months. If I don't see disease in the summer I stretch the time between applications as much as possible. I rotate FRAC groups (modes of action) to keep the disease from developing resistance. If spraying any fungicides, organic or synthetic, use the protective clothing as stated on the label. Sorry if this is too technical but I have a minor in Chemestry and a Masters Degree in Horticulture .
[Last edited by MJOrwat - May 14, 2019 6:39 PM (+)]
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PNW (Zone 8b)
Aerith
May 15, 2019 2:21 AM CST
Matt, hi,

Thanks for your sharing about dealing with BS. I am a newbie and would like to ask for advice about powdery mildew which is the major problem of my roses.

The weather here is usually cool and damp except summer since I live in Seattle area. What can I do better when my most roses get PM more or less except Rugosa, China, and some OGRs? The worst are HTs and floribundas indeed though I've tried to choose disease resistant varieties. I would rather not use systematic treatments because of honey bees and other beneficial insects, but foliage spray isn't waterproof. What I do is using neem oil and copper spray after raining or just before a few sunny days. So far, not very useful.

To be honest, I'm not a good gardener, and growing roses is purely a labor of love for me. I know PM don't really kill plants. I just don't want to see them suffered from disease. Alas, maybe it's my problem instead of their's.

Hope it's not OT too much. I tip my hat to you.
[Last edited by Aerith - May 15, 2019 2:27 AM (+)]
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Name: Luis
Hurst, TX (Zone 8a)
Dog Lover Region: Texas
luis_pr
May 15, 2019 3:44 AM CST
Consider using drip irrigation or soaker hoses that will not get the rose's foliage wet like a sprinkler does. I switched when my sprinkler broke and Crape Myrtles and hydrangeas suffered from powdery mildew and other fungal diseases. BS is still around but not as bad as before. I also gave up on roses (kept healthy looking ones and stopped buying any more) when this area became Rose Rosette Disease Central.
[Last edited by luis_pr - May 15, 2019 3:47 AM (+)]
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Name: Matt
Florida Panhandle (Zone 8b)
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MJOrwat
May 15, 2019 6:05 AM CST
If you're looking for a product that doesn't have any residual but will kill fungal spores by acting as a disinfectant try Consan 20. It has one drawback. While safe for the environment, it is very caustic to skin, like a heavy duty acid, when concentrated. So you MUST use chemical resistant gloves to the elbow.
Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
May 15, 2019 10:03 AM CST
Has anyone been successful in preventing BS disease by planting garlic in a ring around the rose bush (I think I read 12" away). Only my yellow roses (Gold Medal and King's Ransom) are plagued by it.

Also I thought I read that powdery mildew only appears when the weather is dry, and a spraying or misting on the foliage will get rid of it. No? I don't have PM on my established roses, but a lot of the bareroot ones I bought (from Lowe's) and put into pots or the few I went ahead first and planted when the soil was really too wet to do so, have PM, some severe. It's nice to know PM won't kill them.

Coastal Southern California (Zone 13a)
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jerijen
May 15, 2019 1:48 PM CST
Aerith --

The main fungal disease for my area is powdery mildew.

In our exhibiting period, we sprayed regularly, to prevent mildew (and the occasional outbreak of blackspot.) We did that, weekly, until a dog we loved very much began to seizure, like clockwork, every time we sprayed.

That was it for us. Spraying ended immediately.

It took a full year for the effects of the chemicals to diminish to the point where the garden filled with beneficial insects, bug-eating birds, and lively lizards.

Any roses that could not, for the most part, grow healthily without chemicals were removed. And that is my "disease-control" recommendation.

It's taken a few years, but we have a healthy rose garden, sans any chemicals.

Thumb of 2019-05-15/jerijen/6c5e16

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Name: Porkpal
Richmond, TX
Charter ATP Member I was one of the first 300 contributors to the plant database! Keeper of Poultry Farmer Roses Raises cows
Garden Ideas: Level 2 Celebrating Gardening: 2015 Plant Identifier
porkpal
May 15, 2019 2:15 PM CST
Healthy and BEAUTIFUL!
Porkpal
Name: Matt
Florida Panhandle (Zone 8b)
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MJOrwat
May 15, 2019 2:18 PM CST
Different fungicides have different effects based on chemistry and application frequency. I've got loads of animals and beneficial insects in my yard....... and 2 healthy dogs. I spray twice a month. When I do I keep the dogs out of the yard until the spray dries. And many of the old climbers in the fenced area don't get sprayed at all.

My advise research whatever you use and be aware of it. Only use and grow what's comfortable to you. There is no "perfect" gardening method.
PNW (Zone 8b)
Aerith
May 16, 2019 1:20 AM CST
Thanks for all the advice. Since this is my first season growing roses, I think I'll keep the way what I'm doing and see how they perform when the very dry summer comes. In couple of months the front yard is going to be renovated, and a drip irrigation system will be included. After I put these young roses down to the ground, I can see what will happen and decide what's the next move. Trust me, I'll ask more questions at that time. LOL.

And Jeri, your garden is fabulous! I love it, and the dogs as well.
Name: Carol
Alberta, Canada (Zone 3b)
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Canadian_Rose
May 16, 2019 11:51 AM CST
Jeri - wowza!!!! Drooling What a fabulous, fabulous garden!!!! Unbelievable!!! Nothing like that exists here. And I love your long haired dalmations!!!
Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
May 16, 2019 3:20 PM CST
Jeri, you have a rose paradise! Thank you for sharing. Thank You!
Name: David Tillyer
New York City
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BigAppleRoseGuy
May 18, 2019 11:55 AM CST
Hi folks.
This spring we have had so much rain that my roses have spread and shot up and I'm very worried about fungal problems.
We had a period of 32 days with rainy days that was really tough. Too much of a good thing, you might say.
I've been worried about blackspot and so I bought the stuff, that used to be branded Bayer, but has just changed names, and
waited for the rain to pause so that I could go out and spray.

I went out today to spray and found that what were nicely spaced rose bushes are now crowded and vying for space.
I sprayed and sprayed and sprayed, but now I'm going to have to prune to get the maximum benefit. I will wait to the
first flush of roses before I cut everyone back. I do love rain, but....
David

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