In her comment on my last rose post, Kerri from Colors of the Garden asked how I combat blackspot. The answer is complicated, but I’ll try to tackle it.
First, I do everything the experts tell you to do.
Plant roses in the sun. This may seem elementary, but roses need plenty of sunshine to produce more flowers and increase their resistance to all diseases.
Give roses enough food and agua. Roses are heavy feeders, and they get stressed without plenty of food and water. In the hot summer, when all of my plants, including the roses, are stressed, I spray them once a week with Sea Tea. I love that stuff. Like humans, when plants get adequate food and rest, they are less likely to get sick. You can also make your own compost tea, if you’re so inclined.
Provide roses with good air circulation, Roses like their leaves dry. This also helps with the occasional powdery mildew Oklahoma roses get in early spring.
Water roses from the bottom. Again, we’re going for dry leaves. I used soaker hoses for years, and now I have Netafin soakers as part of my irrigation system. If possible, water them in the morning.
Mulch plants. Our enemy, blackspot, multiplies in moist soil. During rain or irrigation, the spores will splash up onto rose leaves, starting the next round of disease. Mulch helps to block the spores.
Clear out leaf debris. Remove any leaf debris under the plants and throw it away. Do not compost diseased leaves unless you’re sure your compost pile is hot enough to destroy the spores.
Keep tools and implements clean. When pruning a diseased rosebush, wash pruners or any other tools in a mild, ten percent, bleach solution before using them on another rose. Also, switch out gloves and wash those used on infected shrubs in hot water. Blackspot spores can be transferred.
Leaf stripping. In the spring, if a particular plant is covered, and it is extremely hardy, strip the leaves, and let it start over. It will recover, and the new growth has a better chance of not being reinfected. However, I would not try this with a grafted rose. I strip the leaves of ‘Reine des Violettes’ because she is particularly prone to blackspot in the spring. Destroy the infected leaves. If a minor outbreak occurs, remove the infected leaves and destroy them too. I carry a small bag around with me in the garden for this purpose. Sometimes, I can stop blackspot before it takes hold.
Buy disease resistant varieties. Probably the most important tip of all. By listening to the buying public, hybridizers are continuing to create more disease resistant varieties. Health concerns and general busyness have changed the market for the better.
In spite of all these precautions, into every garden, a little blackspot must grow. So, what can be done to control it once it occurs?
Start with the least toxic prevention and control first. If I have time, in February, before leaf break, I spray a combination of lime and sulphur on my plants. (My, doesn’t that smell good?) This spray prevents some pest and disease problems and is a natural barrier. Spray in the early morning hours if you can.
In spring, before temperatures rise to 80 degrees daily, you can spray a solution of one tablespoon of baking soda and one tablespoon of horticultural oil mixed with one gallon of warm water Although I’ve never had much luck with this on blackspot, I have noticed it works well with powdery mildew. Any higher temperature, and the oil will burn the leaves.
I’ve used Neem oil with some success, but it is an oil, so that 80 degree rule still applies. Also, I think it smells like something rotten, so get ready. Neem oil is a fungicide and an insecticide, so it also helps with insects. Conventional wisdom cautions spraying it around bees or ladybugs. Neem oil is possibly toxic to them, although not to us, so spray it early in the morning before the bees get started. Green Light Organic Rose Defense – Pint #07516 is made from Neem oil if you’re interested.
For more organic tips, see The Organic Rose Garden, by Liz Druitt. I have to agree with her when she writes about tolerance:
“You don’t have to know the solution to every rose problem if you can learn to see beauty in good health overall, without demanding total perfection. It’s even possible to grow show-quality blooms on a bush that has blackspot on a few leaves.”
I do, occasionally (perhaps twice a season), spray only those bushes which are in full and total breakout. When I do, I use Ortho Garden Disease Control Concentrate – Pint #0297660, which has Daconil as its chemical ingredient. Of course, once you read the Pesticide Action Network’s page on Daconil, you may want to reconsider using it. Note, that there are even stronger chemicals used by large rose growers, but I won’t list them here.
If you do decide to engage in chemical warfare, suit up in full hazard gear: long pants, long sleeves, gloves, and a respirator mask because many chemicals are potential carcinogens.
There are a few roses I want to grow which have scent and beautiful flowers. Unfortunately, hybridizers are still trying to get the disease resistance and scent thing to occur consistently in the same plant. When they do, I will be dancing in the street. In the meantime, I do all of the above to combat blackspot, but I start with good garden practics.
Each year, I spray less and less, and frankly, a lot of my roses have blackspot in the middle of summer. I read somewhere that so do Queen Elizabeth’s roses, and if she doesn’t mind, then neither do I.
Thanks for all the rose care tips. I need them! My roses are doing well right now after struggling tremendously this past summer. I’ve learned so much visiting your blog. Have a great holiday,
Aiyana´s last blog post..Fearless ~ Green Thumb Sunday
Aiyana, you’re welcome. Thanks for continuing to come by and read.~~Dee
Great post, Dee. Who doesn’t love roses? They’re still reigning Queen Supreme in the garden as far as I’m concerned.
My favorite black spot remedy is liquid copper spray which is approved for organic use. French farmers have been using this for over a century to control diseases on grapes. It is both a pesticide and insecticide, depending on the mixture you buy. I’ve seen it cure some pretty tough cases of blackspot.
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Hi CG, yes I’ve also used copper. I like the type which is already bound with a sticking agent. I’ll be honest. It only kind of works on the blackspot here. I think it’s the combo of heat stress and high humidity mixed with water stress that makes it so difficult in Oklahoma.~~Dee
Hey there Dee…A very thorough post…you’ve answered my questions and now if I decide to expand my rose collection beyond Fairy Queen, New Dawn and Carolina Rose…I will know what to do! Besides I know you would be glad to help! Gail
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Gail, you’ve got some good ones already. I’ve never grown Carolina Rose. I’m glad I could help.~~Dee
organic gardening guy
Amazingly beautiful roses. I have always had bad luck with them other then the small Bush Roses. I am going to bookmark this post I do recall some black spots. TY for the great information and happy gardening:))
OGG, thanks for stopping by. I’m glad to help. We, gardeners, must all stick together.~~Dee
Great tips Dee. I do a lot of these but have never heard of leaf stripping. I put up with blackspot, especially in the winter since I’m not out there in the garden. Your best advice, to get those disease resistant varieties, is a good one. But sometimes you just have to have that one rose! That’s my relationship with Marie Pavie. I’ll suffer blackspot for its fragrance and lovely little blooms.
Jean´s last blog post..Garden Bloggers’ Blooms Day – Dec 2008
Jean, now see, isn’t that funny. I don’t usually get any blackspot at all on Marie Pavie. Just shows that different climates have different challenges.~~Dee
Mr. McGregor's Daughter
Thanks for the tips! I did plant a disease-resistant Rose, but I know that’s not disease-proof. I will take notes.
Mr. McGregor’s Daughter´s last blog post..The Journal
None of them are bullet proof are they . . . .~~Dee
Dee, I’m bookmarking this post to refer back to next year when I attempt to grow roses (again). I have seen those knockout roses around here, and they ARE magnificent! Thanks for the tips.
Nola, that is such a high compliment. Thank you. Call me before you plant anything. I’ll tell you the best ones for Texas.~~Dee
Hi Dee. No doubt, roses are indeed beautiful and your pictures are eye candy! Nice job! But, black spot is certainly one of the single biggest reasons more people don’t grow them. In my travels, neem oil is the most popular organic product for prevention and control but as you mentioned in your post, use with caution plus, the non-selective pesticide issue bugs me a bit. Anyway, there is a fairly new product on the consumer market (although used in commercial production for years), that is worthy of attention called GreenCure. Just for the record, I have no affiliation with this company or product so this is just a heads-up to your readers to look into this. It’s not an oil, but a powder you mix with water. It’s not a pesticide either, just a natural disease control. We tested it over a growing season in 2006 and were so impressed with the results in fighting black spot, my company named it as one of the 10 “Best of the Must-haves” for 2007 as we went on the road to tell gardeners about these products. We especially liked it because it was safe for organic production since it’s simply potassium bicarbonate (similar to using baking soda as a treatment for black spot). Studies showed this to be more effective against it and many other plant diseases as well. Dr. Ken Horst of Cornell University developed this and is a respected plant pathologist. They have a website if you want to learn more: http://greencure.net. Thanks.
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Joe, I’ve thought a lot about your comment. I think I’ll contact the Greencure folks and ask if I can test their product. Anything to make growing roses easier.~~Dee
My roses always get black spot and look dreadful but I have decided I either have to put up with it or not grow roses! I grow varieties which are meant to be disease resistant but they are tested near a city and living in the country (near the sea) our cleaner air means I get black spot. Perhaps next year…
Best wishes Sylvia (England)
Me too, Sylvia. I didn’t know cleaner air would effect blackspot, but makes sense. The dirtier air probably has chemicals which inhibit the spores. Interesting.~~Dee
Whatever you are doing, it must be working Dee. Your roses sure are grand.
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Thank you, Tina, honey. Thank you.~~Dee
I got rid of all my rose chemicals last year. Now I put up with a bit of blackspot, but it doesn’t seem bothersome–and it seems less than when I used them.
Great advice. Wish I had more sun!
I wish you did too. That way you could have more Austins since they do so well for you.~~Dee