Any chance of posting pictures They sure would help us.

Also need info about where they are -- pots or the ground?
How do you decide when to water?
And how much water do you apply?
Prevailing temperatures?
Anything else you can recall?

this is one of the reasons.. i gave up on cukes long ago ...

for a myriad of reasons.. they just die ...

you either dont end up with enough ... or you are buried to the gills ... lol ...

simply googling: diseases of cucumber ... got me to the link below.. along with 3.3 million other hits ...

ken

ps: i wonder how much heat is retained under your row cover in august ... got to be steamy under there ....

Here is a link that might be useful: link

Thanks for helping, here is a photo:

Basically,I water them if it doesn't rain for 3 days in a row. There has been plenty of rain this year so far.

The same image, along with my response, at
http://forums.gardenweb.com/forums/load/pests/msg0809184828165.html

Needs water.

Here is a link that might be useful: my answer