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  • Treating Powdery Mildew on Squash

    Created by leaird on

    My squash plants have white powdery mildew, which has begun to spread to my zucchini and cucumbers. I went to Lowe’s to purchase a treatment for the mildew. I was advised by two garden center employees to use Disease Control, which is manufactured by Bayer Advanced. The active ingredient is Tebuconazole (2.9%). We sprayed the plants last night and checked on them this morning. The white powdery mildew did not seem to be affected by the fungicide. So, I called Bayer’s 1-800 question line. The woman informed me that this product is not to be applied to plants used for food. She could not give me any further information. The Poison Control Hotline and the National Pesticide Information Center could not offer any additional information either. If you have any information concerning this fungicide, please share. I am heartbroken at the thought of having to destroy my garden that I have worked so hard on.


  • Author
  • #13836


    I Googled tebuconazole and found that the product is a possible carcinogen and a potential water contaminant. As for toxicity, it is moderately hazardous. With that said, I'd stay clear!

    I'm always amazed with the "crap" you can purchase from most garden stores.



    There are natural products for getting rid of powdery mildew, although this is a bit late for your post last year.

    First of all, don't panic! At the first sign of trouble, clip off and destroy all affected leaves. If the plant is already covered by the time you realize the stuff is there, cut the plant right down, leaveing no leaves, if it is early enough in the spring the plants will continue to grow, even though it looks as if it is done for.

    Here are some tips to prevent this from happening this year. Powdery mildew is usually crowding which causes poor air circulation, when you water, aim the hose at the ground, I use soaker hoses by laying them in between two rows of produce when I plant the seeds. This way, you are not going to disturb the new seedlings, and while this may be expensive to start, what I did was buy a few soaker hoses each year until I had enough for my whole garden and now I don't use a sprinkler or spray hose at all. For another thing, in these green days, watering via sprinklers and hoses is wasteful and expensive.

    Powedery mildew usually starts when the days are hot and the nights are still chilly and condensation sits on the leaves.

    To receive a recipe for dealing with powdery mildew, e-mail me.



    It's literally a mildew that, when the leaves dry (and the humidity lowers) turns into powder (hence…the white color). The bugs walk across it on their way to their garden party (sorry…couldn't resist)…and track it to the next plant. Most 'maters and peppers are resistant, but your herbs: especially the sage, might be the next on the "hit" list.

    How to get rid of it??
    Lots of different ways really, it just depends on how organic, concerned about your ground water and bees, you are…..versus….the ole attach the noxious poison in a bottle to your hose end, add water, and just hope it works…..that I hope (since you have added organic sail)…you aren't.

    There are lots of remedies:
    1: only water in the morning. This allows the plant leave to dry throughout the day, limiting the fungal production
    2: cut and remove any heavily affected leaves of the plant. i know they are pretty when they are full, but a squash plant with 4-5 healthy leaves will produce far more product than one that is dead from the fungus.
    3: dispose of those leaves as far away from your garden as possible. DO NOT COMPOST!
    4: Dry rub the remaining, healthy(ish) leaves with paper towls to remove the loose spores that can be caught in the wind or tracked to other plants by vagabond critters.
    5: Keep an eye on everything else too….and especially (although I didn't mention it before): get rid of the Japanese Beetles!! They are the absolute WORST for spreading this….

    Now…..There are some fungal control agents that are organic, (and the ones that aren't….but I don't use them so….)and of course both are available at the usual outposts: Lowes/Home Depot. Some people do this funky milk wash down thing, but…. Personally, I've always had the best luck when I subscribe to the clip it back, wipe it off, water at night, thin out your space to increase breeze methods….and I've even tried wiping the leaves down with oil if they weren't too far gone….I can't swear that the oil thing helped…but is sure didn't hurt.


    Eric Vinje

    Hi Elizabeth –

    Powdery mildew is the most common and widespread of fungal diseases attacking plants. There are several techniques for treating it without resorting to toxic chemicals. I’ve listed many of them here.

    • Stake plants to Improve air circulation
    • Prune away leaves and stems as soon as you see signs of mildew. Make sure to disinfect pruning shears after each cut.
    • Use a thick layer of mulch to prevent disease spores from splashing onto leaves.
    • Keep leaves dry when watering. Drip irrigation and soaker hoses will help with this.
    • If powdery mildew is present, treat with a least-toxic organic fungicide. We often recommend Green Cure, Bi-Carb or Actinovate for the job.

    Please see the following link for more information.


    Good luck!

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