best fungicide for apple scab on flowering crabapples

Discussion in 'Fertilizers, Pesticides and Diseases' started by americanlawn, Apr 29, 2019.

  1. americanlawn

    americanlawn LawnSite Fanatic
    from midwest
    Messages: 6,078

    I only spray 2 times each spring. Been using Eagle 20EW. Results vary year to year. Anything better to use?
     
  2. brookviewlawncare

    brookviewlawncare LawnSite Senior Member
    Messages: 401

  3. OP
    OP
    americanlawn

    americanlawn LawnSite Fanatic
    from midwest
    Messages: 6,078

    Captan requires spraying at 7 - 14 day intervals. It is a "contact" fungicide .. not systemic, which I was looking for.
     
  4. Trees Too

    Trees Too LawnSite Fanatic
    Messages: 5,095

  5. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 15,813

    Our local tree company is using propaconizole on our crab apple tree.
     
  6. Mark Oomkes

    Mark Oomkes LawnSite Fanatic
    Messages: 18,548

    Results vary because the weather varies.
     
    rlitman, Trees Too and Walker56 like this.
  7. rlitman

    rlitman LawnSite Silver Member
    Messages: 2,186

    You're looking at it the wrong way. Fungicides are prone to failure with resistant diseases. This is more a problem if you stick to a single fungicide, or use ones that work in the same way, not knowing that they're essentially identical. Also, mixing several similar fungicides is going to overdose your plants. With the systemics listed above, that will cause stunting, as they can moderate growth (overdosing on contact fungicides can cause burning).

    Look up the FRAC code of the fungicide you're using, plus the codes of any potential replacements, and choose two systemic fungicides that have different codes that are rated for your target (since you say you're doing two applications). Then ALSO choose a contact fungicide (I'd suggest chlorothalonil, but captan is an option too).

    Now use one systemic fungicide PLUS the contact tank mixed for your first app, and the second systemic plus the contact with the second app. Or just keep it simple and do two apps with the same pair if resistance isn't causing you huge problems.

    The secret here is that the contact fungicide will almost certainly be a different FRAC code, so mixing the two will rule out the possibility of resistance.

    Anyway, treating plants with fungicide is more a preventative than curative process. At best, fungidide stops the infection, but the plant still needs to grow out of the damage. You want to prophylactically treat your leaves when they're still young, so time your treatments around your plant's growth cycle. In the case of your crab apple, two spring treatments may be just about right, as your first spray should be just as the tree starts to leaf out, and the second, a few weeks later as the canopy is complete.

    My personal experience has been that wet springs don't necessarily lead to fungal infections, until late in the spring as you get hotter nights. The early spring cool evenings seem to keep the fungus at bay here.

    There's a good discussion of it here FYI:
    https://extension.umn.edu/plant-dis...ornamental-crabapples-from-apple-scab-1794910
     
    Last edited: Jun 29, 2019
    americanlawn and hort101 like this.

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