White powder on zucchini and yellow squash leaves?

mamessnerSeptember 26, 2011

I seem to have some sort of fungus or pest leaving white powder on my zucchini leaves. The powder started on one large leaf, and within a week had appeared on most of the leaves. After browsing the forum I initially thought it was mealy bugs, but the powder is more widespread and I haven't seen any insects that resemble mealies.

The fruit seems unaffected - I've had a great yield so far.

Now the powder seems to be spreading to my other (yellow crookneck) squash plant, but isn't affecting the tomatoes or herbs that are growing in close proximity.

These are growing in a hydroponic garden, if that makes a difference.

Bonus points if you can identify and help me treat the little worm trails visible on some of the leaves, as seen in the photo.

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powdery mildew... common on squash late in the season...
leaf miners... what do i win? :)

    Bookmark   September 26, 2011 at 9:38PM
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definitly powerdery mildew. Can be caused by watering over the top of the plants. Will spread and kill all your squash plants if not treated. There are several online recipes for spray on treatment. Definitly remove affected leaves and dispose of in sealed garbage back.
I had this. It started on my yellow squash and killed them all before I knew what it was and how to treat it. Then it moved over to my zucchini plants. I was told it was most likely because I watered from over the top of my plants and got the leaves wet.

    Bookmark   September 27, 2011 at 1:00PM
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Perfect. Thanks so much for the help. I only water at the base (hydroponics), but it's been raining lately, and I think my sprinkler overshoots the lawn too.

biscgolf - You win the satisfaction of knowing that you helped out a fellow gardener who is very appreciative. :)

    Bookmark   September 27, 2011 at 1:29PM
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Powdery mildew is everywhere, all the time, and just makes it's presence known when the conditions a favorable. There is no sense in messing around with garbage bags and such, because when you move anything with powdery mildew on it, you spread spores anyway. Besides, if something has it, odds are the spores are all over your garden. The problem I have where I live is that it's very humid in summer, so every single morning there is plenty of dew on everything, making conditions favorable for powdery mildew. Not to mention the row of lilacs at the egde of my yard that get it every single year without fail.


    Bookmark   September 27, 2011 at 5:59PM
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chudak(10 San Diego)

@dolivo actually powdery mildew does not like water and you can suppress it by spraying your plants in the mornings with your hose to keep them humid.

Preventing and controlling powdery mildew Interestingly enough, the most effective measure in preventing and treating powdery mildew is to spray the foliage of your plants daily with plain water from the hose. Powdery mildew hates water! The only caveat with this method is to be sure you do it early in the day so that the foliage completely dries before cooler evening temperatures arrive, otherwise you may invite other fungal diseases, such as black spot, into your garden.

    Bookmark   September 27, 2011 at 8:37PM
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rhizo_1 (North AL) zone 7

Chudak is absolutely right. Few people seem to realize that a good spray of water can wash powdery mildew away, as long as it is caught early and done frequently. With an infestation such as yours, I'd be mighty tempted to spray with a Neem application to get it under control. don't spray in the hot part of the day or when the sun is blazing on the foliage.

PM is one of the very rare fungal pathogens that does NOT require water to thrive. It likes humid conditions, but not sprays of water.

    Bookmark   September 27, 2011 at 10:56PM
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So...I have another zucchini fungus question. My zucchini leaves are large and beautiful, but there is a white/silver coloring following the veins and lines on the leaves. It doesn't look like the powdery mildew I have seen in pics. Does this sound like mildew? Someone else posted a pic of what it looks like and sid it was the way the leaves are?? Any thoughts?

    Bookmark   June 6, 2012 at 10:16PM
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yaya, that is probably just the natural habit of your type of Zuchini. I have some like that this year and they are producing well.

    Bookmark   June 7, 2012 at 8:09AM
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    Bookmark   June 7, 2012 at 9:08PM
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