Battle with blackspot on Roses.

[Anonymous]

I am fairly new to Rose gardening and have one hybrid tea rose (Chihuly) right now. I have the plant in a large plastic pot where it has been for 2 years, here in the Dallas, TX. area. For two years I have been removing leaves that appear infected, and spraying the top and bottoms of the leaves with the ortho commercial fungicide (chlorothanonil). I didnt think it was helping much because this is a constant battle, having to remove leaves, pick up the dead ones, spray, etc... every week... I recently decided to try baking powder (I didnt have baking soda), vegetable oil, and insecticidal soap. Mixed the appropriate levels of each, and sprayed... Since approximately 1 week, nearly half of the leaves appeared infected, and most have dropped off. I want to keep the rose, but I want to try and kill this fungus somehow... ill try anything. I even thought that I would wait until fall temps dropped and I would pull the plant out of the original container, remove the soil completely (bare root) and cut back the topgrowth. Bleach the container, discard the soil, and lightly spray the outside surface of the rose plant with a 1/10 mixture of bleach or soak the plant, etc.. for a brief period of time. What can I do? Anything?

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[JoeSpareBedroom]

1) Insecticidal soap will serve no purpose in the spray you made, and might mess with the pH, which IIRC is the reason baking soda is sometimes effective. 2) When you say "large plastic pot", how large, in height and width? 3) Spend some big money on a really big box of baking soda. Baking powder is not a viable alternative. 4) Describe the placement of the pot, relative to sun, wind, other plants.

[JoeSpareBedroom]

Mixed with water and sprayed on. It then dries, leaving a bit of a film.

[Gravelle]

Is the baking soda just sprinkled on the leaves, or is it mixed with something else?

Thanks.

[Kay Lancaster]

Baking powder is the wrong stuff, and a whole lot more expensive than baking soda. A pound will set you back less than $1.

Blackspot is a fungal disease, worse during warm humid weather. The spores are pretty ubiquitous. It tends to be worse on stressed plants, and plants in pots are almost by definition, stressed.

Your choices are a regular program of spraying and sanitation, learning to live with blackspot, or choosing disease resistant cultivars

American Rose Society has chapters all over:

and there is also a Houston Rose Society. A&M maintains a list of very disease resistant roses: -- you may find one there you like better and is a whole lot easier to grow for a beginner.

Kay

[Flora]

I usually mix baking soda 1 tsp to a litre/quart, though I suppose you could use more (until your sprayer nozzle blocks up).

I read about using skim milk, possibly in rec. gardens. roses, and tried it. Apparently there's a protein in the milk that stops black spot from replicating or sending out spores. You use skim milk because it has all the protein and none of the fat of 2% or h*mo, which can stink up your plants. It's fairly cost effective, and easy to do.

You mix 3 parts water to 1 part skim milk.

I've tried it on my roses and think it's as least as effective as baking soda, and maybe even a bit better. It won't get rid of the black spot that's already there, but if you spray it twice a week, and after every rain, you'll probably see new healthy leaves growing. I also spray the ground around the plants as there are spores in the earth as well.

Flora

[Gravelle]

Thanks, Flora. I'll give this (skim milk) a try.

[Myrl Jeffcoat]

You guys are on to a topic that I have been wondering about for awhile now. I have a small rose garden in the front of my yard, which contain

7 rose bushes. All bushes appear very healthy, except for one near the middle. Every year, it starts out ok in the Spring, but by Summer it has developed the Black Spot that you are speaking of. No amount of spraying, or treatment has brought it out of it. Then the following year, it begins the cycle all over again. The first blooms of this bush is amazing, they are absolutely abundant and beautiful, but the bush does frustrate me.

I'm thinking of simply digging it out, and replacing it with another of the same variety. . .Whatya think? Could this just be a weak bush, that is more problem than it's worth?

Myrl Jeffcoat

[JoeSpareBedroom]

Well, it could be that you've got a bush with absolutely no resistance to disease. And, I've also read over the years that real rose fanatics plant with a lot of space around the roses, for better air circulation. It seems to me they'd have to be VERY crowded in order to cause problems, but maybe not.

[Myrl Jeffcoat]

That's my take on it too Joe!. . .I think I just have a sickly bush! The roses aren't that close together, and their is plenty of air circulation around them, because they are out in the open, not even up against a fence.

This January, I'm yanking that one out, giving it a proper burial, and I'm going to replace it. . .No looking back;-)

Myrl Jeffcoat

[JoeSpareBedroom]

Every now and then, I pretend for a few minutes that bud-eating deer don't exist in my yard, and I entertain the idea of planting some roses. At those times, I look at one of my books which reminds me that one entire category is pathetically weak with regard to fungal diseases, and need more chemical support than any plant deserves, sort of like green seedless grapes. If I recall, it's the hybrid tea roses. You should probably do some reading before choosing your next rose. You obviously got lucky with the ones that aren't having problems.

[Kay Lancaster]

They'll also do well with decent soil, a little fertilizer and water and some benign neglect, if well chosen.

Quite a few current breeding programs stress developing disease resistant, resilient cultivars.

[JoeSpareBedroom]

True. In my previous house, I had "beach roses" - rugosa, I suppose. Utterly bulletproof. No diseases, they laughed at chunks of ice that fell from the roof, and they bloomed from spring until heavy frost. They were single flowers, which don't make rose worshippers' hearts flutter, but they scented the whole yard.

[Ann]

"JoeSpareBedroom" expounded:

I love them for that very reason - their perfume.

To me, no matter how beautiful a multipetaled rose is, if it has no scent, it's just not going to grow in my garden.

[dr-solo]

when I was in my "rose" phase I became aware of how important early morning sun and good ventilation is to drying off the bush. and needless to say, no watering after morning that would get the leaves wet. Ingrid

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[Stephen Henning]

We live in moist humid Pennsylvania. We moved here from Portland, Oregon where everyone grows beautiful roses. Here in PA the leaves were always various shades of green, yellow and black and falling off except one plant. This plant was a climbing rose growing next to our porch. Those leaves that were out in the open, facing southeast were green, yellow and black. However, those leaves that were on stems that were growing under the porch roof never had any black spot. It seems that the black spot just came from the morning dew which we have just about every day in the summer. Stems free from morning dew were free of black spot.