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racin_rose

Cercospora??? Anthracnose??? Both??? Plague???

racin_rose
10 years ago

The weather around here made a pretty drastic change and...BAM! I've got some super spores on my hands. Can anyone help me out with this? Normally Bonide Infuse (propiconazole) Ortho Disease Control (triticonazole) and Rose Pride (triflorine) work for me but...this stuff seems pretty tough...first attack I've had all year that's concerned me.

Thanks all.

Comments (10)

  • racin_rose
    Original Author
    10 years ago

    More

  • racin_rose
    Original Author
    10 years ago

    Again

  • racin_rose
    Original Author
    10 years ago

    Again

    {{!gwi}}

  • IanW Zone 5 Ont. Can.
    10 years ago

    My vote is Cercospora............

    Here is a link that might be useful: Cercospora on roses

  • racin_rose
    Original Author
    10 years ago

    Again

    {{!gwi}}

  • michaelg
    10 years ago

    It is hard to tell cercospora from anthracnose in the first weeks. Spots of cercospora will show through on the bottom side. Blackspot usually does not, and I don't know whether anthracnose does. Spots of cercospora will coalesce to form large brown dead areas, but this might take a month. The centers will usually drop out of anthracnose spots, but again that takes time. Many roses are resistant to anthracnose. Roses bred for the North, such as Canadian Explorers and Therese Bugnet, may be more likely to get anthracnose. Roses with wichurana heritage, such as Kordesii, Meidilands, and shiny leaved climbers, may be more likely to get cercospora.

    I don't think triforine controls either one. I am not such about -azole fungicides. I have a lot of cercospora despite spraying tebuconazole some this year. Chlorothalonil (Daconil) or copper would probably work. Usually these diseases do not do a huge amount of damage.

    I'd guess anthracnose from the pictures, but without confidence. The last two pictures are not opening for me.

  • trospero
    10 years ago

    What Michael said. Most of the available fungicides don't offer much control of either Anthracnose or Cercospora.

    Given this is September, and the fact that neither of these diseases is likely to cause significant damage, I wouldn't fret over it. Unlike Blackspot, these fungal pathogens wont significantly defoliate a rose.

  • michaelg
    10 years ago

    Actually, Paul, I had some roses defoliated by (mostly) cercospora this year, but I agree that that is unusual.. Our climate seems to be Ground Zero for this disease, and this year we've already had over 60 inches of rain, about 2x the average. Your point about the late season is a good one, since cercospora takes six or eight weeks to kill a leaf on most varieties.

  • racin_rose
    Original Author
    10 years ago

    First of all, thanks to everybody for your insight...there's a lot of excellent information here already.

    Some of the leaves have the necrotic spots described here and in some cases it has produced tiny holes in them. In other instances, irregular sections of the leaves have died and turn brown, particularly on the ends. At first I thought it was heat or fertilizer burn but it would only appear on a leaf here or there. I noticed the burnt-looking parts had discrete, fuzzy black undersides. Then, of course, the spots showed up. That's why I wondered if I'm dealing with both, but if they're hard to differentiate at certain phases...that's good to know.

    Given what's been suggested here I guess I'll just deal with it. Some of my HTs have defoliated low down but look fine up top, and some of the leaves that are only marginally infected seem to not be getting any worse.

    Ians, Michael, and Paul, thanks again. I don't know why the other photos didn't work but I'll try to fix it when I get home.

    This post was edited by racin_rose on Thu, Sep 5, 13 at 15:14

  • michaelg
    10 years ago

    Leaf areas that are killed by fertilizer burn or whatever may be colonized by botrytis fungus, which could produce the fuzzy underside you describe. I would not be concerned about it. The pictured leaf with brown spots along the margin could have suffered fertilizer burn. That same leaf may have cercospora spots that are coalescing into a mass.

    If ashy-looking centers drop out of spots leaving a purple-ringed shothole, that is anthracnose. You can have both diseases on the same plant.

    I agree it is probably OK not to do anything.

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