Rust on Roses

silybum(Sunset 16/z8b)May 4, 2005

Is rust the same as black spot? I think I have rust on my roses. I have a recipe for a spray, 1 tsp baking soda to 1 quart warm water, with 1 tsp insecticidal soap to help the solution stick. Has anyone tried this? I don't have any of the insecticidal soap, is it necessary, or anything else I could use, I do have some Therm X70 (yucca extract) that I use when I make my foliar spray to help it stick.

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LizzieA(z9 CA Sunset 17)

Rust is diffrent from blackspot. Rust manifests as orange spots usually on the underside of the leaf to begin with. Blackspot looks just like its name, a black spot with feathering around the edges, like an inkspot dropped on a paper towel would look like. This is a bad year for rust on my roses too.

What you're refering to sounds like a modified Cornell Formula: 2 Tbsp Horticultural oil (SunSpray usually), 1 Tbsp baking soda in 1 gallon of water - SunSpray contains a sticker so no soap is necessary, with other oils you may need a few drops of dishwashing liquid. Do a search on "Cornell" and you should come up with some interesting discussions.

This is a preventative not a cure. There really is no cure for blackspot, powdery mildew or rust once it's taken hold, just methods of controlling it from spreading further. Other things to use are a sulphur-based fungicide or a copper-based fungicide, and some people swear by neem oil spray.

Pull off the rusted leaves and dispose of them in the trash, they'll turn yellow and die eventually anyway. Do not compost them.

    Bookmark   May 4, 2005 at 4:37PM
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michaelg(7a NC Mts)

Good information from LizzieA.

I don't have rust, but the West Coast organic growers seem to agree that sulfur (such as Safer fungicide) is highly effective, while Cornell mixture is not. Cornell mixture is very good for powdery mildew, however.

Some gardeners use "rust" as an all-purpose term for fungus disease, but rose rust is a particular disease as described by Lizzie.

    Bookmark   May 5, 2005 at 3:24PM
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tinamcg(Z5b Kansas City)

Rose rust confuses me. I was taught that rusts are fungi that require two hosts to complete their lifecycles, but I've also read that rose rust doesn't need an alternate host. Cedar apple rustrs comes from fungi that start out on junipers and end up on crabapples, apples, and serviceberries; some lawn fungi come from buckthorns, and white pine blister rust comes from currant bushes (one reason we pitched our currants). But rose rust is just everywhere, it seems, and getting rid of the alternate host doesn't seem to help prevent it. Is that right?

    Bookmark   May 14, 2005 at 11:59AM
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Ralph_Sarmento(9b)

We have the classical infestation on our roses and now find the same symptoms on our boysenberry and ollalaberrie vines. Is this a common affliction on berry vines?

    Bookmark   June 2, 2005 at 8:01PM
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tinamcg(Z5b Kansas City)

Ralph, the boysenberry is in the rosaceae family, so it isn't surprising that your berries and roses are suffering from the same type of rust.

    Bookmark   June 2, 2005 at 9:25PM
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michaelg(7a NC Mts)

Tina,

There are a number of different species that cause rose rust. Most have five different spore forms or stages. Some species require at least two different host plants, but apparently most of the rose rust species are autoecious and can just hang out on roses. A second stage or spore form is noticeable in the fall as shiny black thingies mixed with the orange stuff.

--via RK Horst, Compendium of Rose Diseases

Once I was unable to convince a poster on the Roses Forum that the black thingies were not insects.

    Bookmark   June 3, 2005 at 5:34PM
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abrodie(z6 ON)

I had 100% success using a solution of 1 part milk to 8 parts water, and sprayed it on the plant. The affected leaves fall off (pick them up right away) but it stops the orange blight from spreading any further.

Brodie

    Bookmark   June 9, 2005 at 9:35AM
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