is it sun scold? How close are they to the lights? They also look really light green almost yellow. Have you provided any nitrogen? Lastly, are you over watering?

Thanks, The lights are not very close at all. I gave them a very light (half strength) fish emulsion after I noticed the gray patches. That was 8 days ago yet they are getting worse. Also, I don't think I'm over watering. I let them get pretty dry before I water

Dave

Thanks. I examined the leaves with a magnifying glass and see absolutely no pests whatsoever. What else could cause the spots?

Dave

At this point, I would give them a shot of MG and try to get it in the ground.

I had this problem a few years ago. Seems like sun burn. I would cut off the affected leaves and give some balanced liquid fertilizer. At the size of your plant fish emulsion at full strength will be fine. Even after doing this to my plants some of them died but may lived!

Thanks, I'm not sure how it can be sun burn. They are indoors under T8 lights. Also, what is MG?

Miracle Grow. If you're trying to stay organic, it's not an option.

And I say MG generically. I just meant any liquid fert because it needs it quick. An organic may take too long to be absorbed. Not trying to support a product one way or the other. I know it is a testy subject from time to time.

Yes, the downfall of staying organic is it's typically slow release and requires microbe activity to break it down. It's not water soluble like the synthetic stuff. However, fish emulsion is already broken down to a usable form, but it doesn't pack the N-P-K that synthetics do.

Don't necessarily need to stay organic. I applied MG but the problem however does not seem to be nutritional nor sun scald as it is worse. I'm afraid the plant won't make it.

If that's the case then just start over. Where are you located? What zone? Any particular reason why you are growing the cucumber indoors?

I'm not an expert but just a few thoughts since I grow in containers as well. How old is your potting mix and what is it?

If the potting mix is new and something like Miracle Gro then you really shouldn't need to fertilize it right away I would think because the stuff already comes with fertilizer which lasts 3 months. If it's something else, what are you using?

If it's older then it will need fertilizer but it also may be compacted which causes nutrient absorption problems for plants .

Since you are growing indoors , that maybe yet another special challenge you have vs. people who grow outside. Being so light green I also wonder if it's getting enough light. Again not an expert but I have seen plants grown in lower light and they are not dark green in color when they could / should be. Silly comparison but white Garlic Chives or white asparagus are both just garlic chives or asparagus grown from the absence of light. In these two cases they are only white because chlorophyll isn't being produced and chlorophyll isn't being produced because they are not receiving light.

What type of grow lights are you using? You may want to browse the indoor growing forum for information. http://forums.gardenweb.com/forums/lights

Here are some really informative container growing links you can browse through to see if anything is helpful.

http://forums2.gardenweb.com/discussions/1379073/container-soils-water-movement-and-retention-xv

http://forums2.gardenweb.com/discussions/1386241/fertilizer-program-for-containerized-plants-ii

http://forums2.gardenweb.com/discussions/1416115/how-plant-growth-is-limited-container-forum-version