Likely same as on your tomatoes -- environmental stress related to water.

Cobra - could you tell us a bit more? Pics are good but background info helps greatly. Where are you located? Were these plants hardened off before planting, how long since planted out, weather especially hot and/or windy or cold and rainy, in containers or ground, how do you water them and have they been kept well watered, etc.?

There is a common disease of cukes called powdery mildew and while this doesn't look quite like it in the pics, it is a good possibility.

Dave

Hi Dave-

I am in southern NH. The plants were started from seed indoors and moved out a month ago. The weather was very warm and dry in May and we had some much needed rain for three straight days to start June. I watered them during the dry parts of May using water from a rain barrel. They are planted in a high raised bed about 4' by 8'. I try to let the ground dry out pretty well between waterings. I use a hand bucket to pour the water on the ground - no constant trickle watering involved.

thanks!

Bruce

jean001a - What type of stress, over or under watered?

You never want to let cukes dry out between waterings. At best you'll end up with very bitter cucumbers. Cukes require consistently moist, not wet but moist, soil.

Did you harden them off well before moving them out to the garden? If not that would explain some of the damage as nothing can go straight from inside out to the garden without a gradual period of adjustment to full sun and wind first.

So are these symptoms on all the leaves, even the new ones, or just the older leaves? Does it appear to be spreading up the plant? Does it rub off with your fingers? Is it more yellow than white or brown? If so then it is Downey Mildew as opposed to Powdery Mildew.

On the cukes, it is yellow and does not rub off. On the tomatoes it is brown and also does not rub off. I do not see any sign of pests on the leaves anywhere.

Drought stress is too little water.
May be wet or moist soil and still be drought stress because of a hot, dry day and/or extra bright day. (Treatment: Rig temporary shade.)

This is not powdery mildew.

And your symptoms don't match that of pix posted by digdirt.

True, we did have a couple of very hot days in late May.