It looks like mites. I just discovered mites killing mine this year and my leaves looked like that. I bought an organic spray but my plants, like yours, are too big now. I'll use the spray next year when the plants are small. I've been successful with simple hard cold water showers with a hose and mercilessly pruning anything infected. Clip any branch that has curled leaves. Check the backside of a fresh green set of curled leaves and look very closely. The way your tomoatoes look in those pictures they should be crawling all over and fast. I can see them with my naked eyes but some people need a magnifying glass. It took me three weeks of heavy pruning and water showers and I kind of have them under control but not completely. I still check every single day and find them albeit far slower and in far less quantities. Sometimes I'd prune a branch and a big spider would jump out at me. The link below shows my despair last year at this date when all my tomatoes were in a death spiral because of mites (but I didn't figure this out until July 2012). Here is a link that might be useful: Last year's tomato failure

For future reference you never cover plants with black plastic bags. The goal isn't total darkness but simply reduced sun exposure for a few days while still letting some sun and air in. A semi-transparent gallon plastic milk jug with the bottom cut out and the cap left off works, so does any of the many row cover fabrics or plant protectors available. Waxed paper cone with some small holes cut in it and wrapped around an upside down 3 ring tomato cage works until it rains. You just have to think outside the box.:) Dave

My guess would be the dreaded leaf miner. If these little specks are lined up together, then that's what they would be. I get them every year, and have them again this year. They are a real pain for spinach and beets, and they cause a good deal of damage if they are left to burrow away. Squish them, and try to cover the spinach with some row cover, but make sure you monitor it regularly. Cut away the leaves that are mined.

Yes. Leafminers. Some make serpentine trails. You have the blotch-forming kind. To manage them this year, keep an eagle eye on the spinach plot then, as soon as you see the beginning of a new blotch, squish that small area between your finger tips. Then next year, plant in a different space and immediately protect with floating row cover, loosely bloused but tucked in along the edges. This avoids the insect which lays the small white eggs on the backsides of the leaves. The reason for the new site is that the insect spends part of its life in the soil.