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Squash - Iron deficiency or d☣wny mildew?

Posted by vgtar z7 copenhagen (My Page) on
Thu, Jun 6, 13 at 16:02

I've got this squash plant with some yellow spotted leaves. It had spend it's childhood in a small shallow dish with a commercial sowing medium. It was the first of the sown seeds to germinate. -The yellowing started a few weeks ago, and I put it off as iron deficiency, since it REALLY needed to get into a big container with good nutrient rich soil. HOWEVER, I saw images yesterday of downy mildew, and I have to say, downy mildew and iron deficiency looks VERY similar in my eyes! Does anyone know how to spot the difference?
I repotted the thing five days ago. The first few days, all the leaves on the plant have gotten droopy in the daytime, but perked up again in the evening. Today, I noticed though, that it is getting less droopy. I guess, these babies, don't like getting their roots disturbed, but even so, it has grown about 30% since I put it into it's new container.

If this is iron deficiency, will the leaves turn green again, or will they stay yellow?


Whole plant:


New leaves look fine (sorry about the tilt, I just noticed it now ツ


Closeup of the biggest of the affected leaves


Closeup of a healthy leaf:


Backside of a yellow leaf (looks fine to me, apart from the discolouration):


I think the white spots (mostly seen on the big leaf to the right) are water/dust marks.




The white spots on this little yellow leaf, are not dust/water splashes, but dead cells:


back of leaf:



Click this link, if you want to see bigger versions.

So, to sum up: Is this downy mildew or iron deficiency? How do I know the difference?
IF it is iron deficiency, will the leaves turn yellow, now that the plant has a a good soil and more room?



*EDIT: I forgot to tell you that the weather has been exceptionally cold this spring, and that it didn't heat up until about a week ago, which makes me think, that perhaps it's too early for downy mildew? -I've never had it on my balcony before, so I'm thinking that if my plants where to get it, then wouldn't the fungus spores first be carried with the wind after a couple of weeks with warm weather?

This post was edited by vgtar on Thu, Jun 6, 13 at 20:37

Follow-Up Postings:

RE: Squash - Iron deficiency or d☣wny mildew?

I think it's a deficiency. I've had mildew on squash as late as last fall when I planted a few in my boxes-- and it didn't look quite the same. I don't know about the progression of this though-- as far as if your leaves will turn back to green or yellow further, etc.

RE: Squash - Iron deficiency or d☣wny mildew?

  • Posted by vgtar z7 copenhagen (My Page) on
    Tue, Jun 11, 13 at 0:46

I think you are right. It doesn't seem to spread to other leaves. If it was downy mildew, those yellow spots would turn into brown wilt at some time, and even if they are still yellow, the leaves seem healthy so far. -Powdery mildew is very easy to recognise, as creates a white "fuzz" on the upper side of the leaf. I think these two are the types, of which they are most receptible.
As for the colouration, well, it is more or less the same as it was last week. Perhaps the yellow splotches have moved a bit further apart, as the leaves have grown in size, but I'm not sure if that is the case, or just in my imagination. -I'm quite sure that the smallest (and lowest) of those leaves looks just about the same as it did a week ago, but then again, it hasn't grown either.

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