John-R
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Help: Small yellow spots destroying my zucchini leaves?

This is my first time growing any kind of vegetable plants, and I'm growing zucchini in containers. They are just beginning to flower, they are about 9 weeks old, and they have actually been doing great. I've put a ton of research into how to properly grow them, but in the past week they have developed many small yellow spots all over the leaves, which seems to be taking over all of the leaves now. They spread out over the entire leaf, and then turn grey/silver. Once the spots turn grey the leaf begins to crumble away, and I haven't seen any kind of recovery; it only gets worse, and worse.
I've googled and searched everywhere online, and I can't seem to find any disease or problem quite like this. I cut most of the really bad leaves off, but more yellow spots are invading fast.
Does anyone know what may be causing this? I've attached a photo of an infected leaf that I left on the plant. In a few days these leaves will most likely be fully yellow with tiny spots, and they will turn silver/grey, and die. Any help or advice is greatly appreciated! I should also mention I'm only growing them organically. Thanks in advance.
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rainbowgardener
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Re: Help: Small yellow spots destroying my zucchini leaves?

The silvery-gray looks a little bit powdery like this?

Image

It's powdery mildew, a fungal disease that cucurbits (squash family) are very prone to.

It is best to treat them preventatively before they develop symptoms. Any of the fungicides (including the synthetic poison ones) work better prophylactically than once the disease is established. Organic anti-fungals include diluted milk, baking soda solution, hydrogen peroxide. You can't use them together, but you can alternate them, since it will have to be redone every couple weeks.

Remove affected leaves and treat all the rest.
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bri80
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Re: Help: Small yellow spots destroying my zucchini leaves?

I'm going to say nutrient deficiency. It looks like you've got them in small pots. Squash are massive plants that spread roots mostly laterally and would quickly become pot-bound in those things.

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rainbowgardener
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Re: Help: Small yellow spots destroying my zucchini leaves?

You are right that zucchini would not do well in small pots, but I never heard of this: ". They spread out over the entire leaf, and then turn grey/silver. Once the spots turn grey the leaf begins to crumble away" as a symptom of nutrient deficiency.

But OP never came back to say whether my picture of powdery mildew looks like what they are dealing with.
Twitter account I manage for local Sierra Club: https://twitter.com/CherokeeGroupSC Facebook page I manage for them: https://www.facebook.com/groups/65310596576/ Come and find me and lots of great information, inspiration

bri80
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Re: Help: Small yellow spots destroying my zucchini leaves?

True enough, but I could see a plant weakened by nutrient deficiency succumbing to a disease. Bottom line, IMO, is the OP's not going to get good results from trying to put squash in small pots. :)

imafan26
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Re: Help: Small yellow spots destroying my zucchini leaves?

Squash does need room for the roots to grow. The ground would be better than a pot and trellising the vines up will give them better air circulation. In wet and humid weather squash will get mildew. Select a resistant variety or you will need to use preventive sprays to stave off the disease longer. Rainbow showed you a picture of powdery mildew, but I think your dots look more like downy mildew. You will see downy mildew more on the bottom of the leaf and powdery mildew on top. It is better to grow squash in summer when there is little rain. Where I live, even with sulfur sprays, I still get mildew because the humidity is 80-99% most of the time. I just try to delay mildew for as long as possible for the squash to get big enough to pick.

https://vegetablemdonline.ppath.cornell. ... _Downy.htm
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