It appears to be ones of the mildew's - best guess downy mildew given the yellow color - but treatment is the same for both downey and powdery mildew - fungicides.

Dave

I doubt that is a Mildew issue but preventative sprays would not be a bad idea. Where are you located? Downey Mildew is now throughout much of the Mid-Atlantic region.

Your leaf spotting is more likely from a combination of metabolic problems and insect damage.

According to the cucurbit downy mildew epidemic map downy mildew is stretching from the Mexican border at Brownsville, TX north-by-northeastward to Detroit, MI...all areas east of that line (and possibly just west of that line) could easily be currently infected with DM. The leaves look much similar to symptoms that I've seen illustrated (and that I'm currently experiencing here in South Alabama). I will say, though, that what I'm experiencing has the yellow spots covering more of the leaves.

I am near Detroit, Michigan. I have not seen any insects so far on any of the leaves. I'll try a fungicide and see if that works. Any recommendations on an organic one? Thanks for the advice!

Downy mildew is definitely here in Michigan. I regularly get updates about various things via email from the Michigan State University Extension and they've confirmed it. DM is also in Ohio and over in Ontario, Canada.

There are several fungicides you can use. A search on this forum will pull up many discussions regarding them.

Rodney

Edit: Here ya go. http://www.gardenweb.com/gardenweb/query/Cucumbers-fungicide/topic=cornucop

It could be angular leaf spot. See how the brown spots stop at a vein?

disease diagnosis curcurbits

mintjulep49, Serenade Bio-fungicide might be something for you to consider.

Agree. While there are a number of "organic" (a mis-leading label) fungicides available Serenade is one that is often recommended. As with all fungicides, both synthetic and "organic", they are primarily preventatives, not cures.

Dave

Is Serenade available in local nurseries or online only? Thanks.

Serenade is sold at Walmart, Home Depot, Lowe's around here. I think even Menards and Tractor Supply carry it. You'd have to call around locally to see who carries it near you.

Dave

I read that "Serenade" is QST 713 strain of Bacillus subtilis. I never heard of that til today. When the weather is continuously rainy and the cucs are covered with yellow spots, I find that "Bordo" copper does the trick. I hope it is not a harmful substance.

From what I've read (no firsthand experience) copper *can* build up to toxic levels so should be used carefully. I've seen where a rotation of Serenade and copper spray has some good results.

Thanks for the warning. I don't use copper or anything else unless the problem is bad. Usually, warm dry weather returns and new growth is okay. Have you found this to be the case also? However, if you live where it's cool and damp all the time, then that is quite a challenge for cucs and similar crops.

Ooooh, we're usually hot and humid. But, this year it has been very wet with some days cooler than normal. Today it is hot...currently 92F and 65% humidity. I haven't been gardening long enough to know if what you've experienced is the same down here. I'm pretty sure that what I've experienced has been DM. I thought hot and humid conditions were more conducive to gardening problems such as insects and disease...????

I've been growing 'Little Leaf' since my 'County Fair' cukes began to develop downy mildew several years ago. 'Little Leaf' is resistant to both downy mildew and the wilt caused by the cuke beetle. I've been very happy with it.

That is very interesting, laceyvail. If you have a few of your saved seeds to spare I would be interested in some of them.