Black spot question

Discussion in 'Rosa (roses)' started by galiano, Jan 4, 2006.

  1. galiano

    galiano Active Member

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    I have an arbour with Climbing Blossomtime on one side. It's 2 years old and was thriving until this past year when it was hit badly by blackspot. It lost most of it's leaves, although a few at the top seem to be clear of any problems. The vines have splotches almost down to the mature wood near the base. Is there any hope for this plant or should I dig it up and start with a new one ? Would cutting it right back to maybe a foot or so above the ground save it ? I am new to roses and don't know if blackspot will spread from the branches to the leaves or to the Climbing White Dawn on the other side of the arbour. Any help would be much appreciated.
     
  2. HortLine

    HortLine Active Member 10 Years

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    The black spot fungus thrives in moist conditions, so try to avoid wetting the leaves during the growing season. Prune plants well to increase air circulation. Once symptoms appear, black spot is very difficult to control. Rake and remove leaves and affected canes in the fall, do not compost the leaves. Before buds start to form in winter, apply a lime sulphur solution (1 part to nine parts water). If the disease persists during the growing season, try spraying a solution of baking soda (1 tbsp in 4 litres of water) mixed with one tablespoon of horticulture oil to make it adhere to the leaves. This can be repeated several times throughout the growing season.
    Black spot is very difficult to control, if it persists more than two years in a row, it may be prudent to plant a more disease resistant variety. Two good sources for disease resistant roses in the Pacific Northwest are:
    Roses for British Columbia by Brad Jalbert; 2003
    Roses for the Pacific Northwest by Christine Allen; 1999
     
  3. galiano

    galiano Active Member

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    Well my dilemma is whether or not I have to cut the canes right back because they have spots left from last season. Or can I prune them as I would and then treat the new leaves as required ? Or does the problem spread from the vines to the leaves ?
     
  4. Ron B

    Ron B Paragon of Plants 10 Years

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  5. Dee M.

    Dee M. Active Member 10 Years

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    It's been my experience that no matter how good your sanitation practices are the spores will come in from someplace. Either resign yourself to spraying alot, learn to live with blackspot [and hope the rose can too] or kill it and plant a resistant variety. I only plant resistant varieties now.
     
  6. Weekend Gardener

    Weekend Gardener Active Member 10 Years

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    You are growing roses in what is arguably the blackspot mecca of the world! Your Blossomtime will not die, at least not immediately, from the blackspot. But it may not thrive. Your best bet is to grow a well nourished strong plant - that's it's best chance of surviving and performing inspite of the black spot. Fertilise it well, water it consistently thorughout the growing season. Give it a location with plenty of sun exposure.

    The next item to pay attention to is sanitary practices. Yes, it's true that hwever clean you keep your yard, black spot spores will eventually get on to your plants from your neighbour's yard. Hence, you can never be in a "black spot free" zone. However, if you reduce the number of spores in your own patch of the neighbourhood, you will definitely cut down the problem to a more manageble size. Spores overwinter in the soil, and in the cracks and crevices on the plant itself. Infected leaves carry thousands of spores, and those are deposited in the soil when the leaves fall. Spores on affected leaves that remain on the plant in the winter will quickly infect new leaves emerging in the spring. The spores are splashed on to the leaves in the growing season and takes hold, creating the unsightly black patches, resulting in eventual leaf drop. (That's why the leaves higher up your climber are the last to be infected). If you keep your rose garden as neat as possible all the time and apply a clean mulch before the leaves unfurl in the spring, you are likely to keep the disease at bay for long enough for the first few months of the gardening season that you will still enjoy the rose. Your rose gets infected by spores travelling in from your neighbours' yard much later in the season. By that time, you would feel totally at ease accepting one of nature's work - blackspot - and just "let it be" - armed with the knowledge that your rose will be back next year.

    If you are so inclined, give the rose a bit of added insurance by applying a dormant horticultural oil spray in the winter.

    No rose is totally immune to blackspot. But as with everything in nature, susceptibility does seem to plot a bell shaped curve in that some varieties are blackspot magnets, whereas some are minimally affected by it. Susceptibility also seems to be influenced by the maturity of the rose plant. I have a David Austin by the name of Eglantyne which I was just about ready to shovel prune because it was annually reduced to just a bunch of sticks by blackspot. But, now, 8 years later, the now 6-8 foot tall shrub of a rose is able to shrug it off. However, there is a lot to be said for choosing varieties that are blackspot resistant. The only caveat here is the observaton that what is blackspot resistant in one area may be a blackspot disaster in other locations. Your best bet would be to scout around your area and observe what does well and what doesn't in public and private gardens.
     
    Last edited: Jan 6, 2006
  7. mr.shep

    mr.shep Well-Known Member 10 Years

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    Excellent post Weekend Gardener!

    Ron, I agree with you and OSU, downy mildew
    has been misdiagnosed for black spot for some
    time, especially in some of the more moist and
    wetter locations in Oregon that I know of. We
    almost never see either disease here in the San
    Joaquin Valley which is one factor why the
    more pre-eminent Rose growing grounds for
    the prominent, well known Rose nurseries are
    just a little ways South of me in Wasco. In
    areas that are notorious for either or both
    diseases then it almost becomes essential to
    grow Roses that have a proven (meaning they
    have proved out when grown in various climatic
    locations) degree of black spot and downy mildew
    disease resistance.

    Jim
     
  8. galiano

    galiano Active Member

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    Last year I had both downy mildew and black spot. I have just sprayed my fruit trees with dormant oil / sulphur and at the same time did all my roses. Will this help the roses ?
     
  9. mr.shep

    mr.shep Well-Known Member 10 Years

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    I've always felt a systemic fungicide would work
    better on Downy mildew and a topical fungicide
    spray works better for Black spot. I think the
    recommendations made in the OSU extension
    article are fine for downy mildew and the baking
    soda and either neem oil or horticultural oil is
    okay for Black spot but a Copper based fungicide
    spray gives us a better preventative and a longer
    acting control in some cases. Still, cultural
    control (clean pruning cuts and good clean up
    of fallen debris) is our main goal but in areas that
    are hard hit by frequent diseases then we may
    have to use a fungicide spray and in some extreme
    cases spray rather often.

    Last year I had both downy mildew and black spot.
    I have just sprayed my fruit trees with dormant
    oil / sulphur and at the same time did all my roses.
    Will this help the roses ?


    Yes, with you having both diseases in the past then
    a dormant spray now was prudent of you to act as a
    preventative.

    Below is an article I would read if I had a problem
    with my Roses..

    Roses: Diseases and Abiotic Disorders

    Jim
     

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