Just read about a Apple Leaf Curl (aka Curly Apple Leaf) caused by a kind of mite. The edges roll up tightly. It's not supposed to be a problem for the tree's health. That said, can you post pictures?

Old topic but wanted to share my input. I'm growing hydroponic tomatoes (various strains) at university in a lab setting (indoors under HID lights) and outdoors in a greenhouse. In one of my greenhouse NFT systems, i recently had a similar problem on 1 tomato plant (total 9 plants that share the same res and tubes). But im gonna try to diagnose your issue by mentioning what others missed out on. 1 major cause of leaf curl is compaction of root system (i.e. roots are compressed or dont have enough space to expand). This risk is exacerbated in hydroponic systems that use tubes. This was the problem i had and had to replace tubes with square tubings that have a liftable top. Once you have access to roots, you must seperate them strand by strand (i.e. so they arent sticking together). In your setup, this risk will further be exacerbated because you filled the entire pvc tube with hydroton (right?). Remove hydroton from tube and place the plant in a net cup with hydroton. Nitrogen burns usually cause browning/yellowing of leaves (similar to sun/heat burn) and not purpling. Test your solution for each chemical if possible, or use a commonly employed aggregated measuring device that shows total concentration in ppm (dont let it exceed 2500). In my system, only one plant was affected. Coincidentally, it was the largest of all plants with the most root mass. I let another normal one grow to its size to see whether it would undergo the same problem, and it did. Viral and bacterial infections that cause leaf roll usually cause it to roll up. Same with the physiological roll. If your leafs roll down AND if your stems bend, this is caused by a diminishing turgor pressure (read: not enough water reaching afflicted area). Mist several times when lights are off (no photosysnthesis) and observe increasing turgor pressure (unbending). Or, untangle roots and remove hydroton from from pipes. I tested various growing methods including fully and partially submerged roots. They all work but a submerged root cannot intake oxygen; it has to borrow oxygen from another part of the plant (i.e. a root part that isnt submerged or above ground stem). This requires energy for transportion and isnt the most efficient (optimal) way for growth and cellular processes. Lastly, an airstone in the reservoir is useless unless the reservoir is completely airtight all the way up to the plant holes. Better to keep small airstones in the pipes right under the plant roots. Those that say aerating the res prevents bacterial development.. is false. If you dont have air in res, you will get anaerobic bacteria (they grow/accumulate slowly but acidify the solution); if you have air in res, you get aerobic bacteria (not acidifying but grow extremely fast). Most bacteria prefer aerobic environments for optimum growth.

I think everyone here has hit the nail on the head. That was my instinct as well, but I wanted to get a second opinion. Fran35, no I haven't used manure at all in my garden. However I do suspect herbicide damage. I've been checking for whiteflies, aphids, etc but I've had a lot of spiders (that I have to try VERY hard to leave alone lol!) and I haven't seen any so I don't think that's the problem. So I pruned up the bottoms a bit (didn't want to do too much and stress them out more) so they're not hanging down in the soil now. I skipped the mulching for now. I'll save that probably for next month. Until we get well into summer, we usually get a fair amount of rain. I spread some organic tomato fertilizer today and I'll have to water it in tomorrow morning. Hopefully that will help. I just read something about too much nitrogen causing leaf roll but hopefully that's not the case here. With all the rain, I highly doubt it. The thing I suspect that has had the greatest effect on at least the upper leaves might be herbicide damage. Everyone around here has been spraying their yards regularly. I googled herbicide damage and the images look just like what I've got here. The good news is, it's not dying back so they should be just fine. I just hope it doesn't get any worse. I know it must be normal for a little bit of foliage to die off, especially around the bottom where it gets old. Plus I would think it needs to get rid of some to put more energy into the top growth. But it still makes me nervous, being a new gardener and all. Am I right about that? It's my first garden so if I mess something up and lose all my tomatoes, I'm going to be so discouraged. But I know that's how we learn. I'd just rather learn from others and not my own mistakes. lol! So last week we had a bad thunderstorm move through. Wind gusts up to 80mph. Yikes! I've lived in Oklahoma my whole life and I don't think I've ever witnessed wind like that before. It blew our brand new grill out into the yard and banged it up. Sad face :( Anyway, I covered my pepper plants with large clay pots since they're still short enough. They did just fine thankfully. My squash plant was even small enough still to sort of be stuffed into a 3 gallon pot. It probably wasn't too comfy in there, but it didn't get any damage! It's HUGE now so I hope our severe weather is over for the season. The tomatoes had some branches that got blown around so hard that they sort of went limp. Only one small branch actually broke off so I spent an hour or so the next day strapping up the weakened ones. All is well now. Anyway, I brought in my potted plants, including a Better Bush tomato. It's working on it's second fruit set and flowering like crazy. In the last few weeks, since harvesting the first of the fruit near the bottom, the leaves at the bottom of the plant have died back. I left the pot indoors for a couple of days because the weather was still a little nuts. I don't think it liked that at all. The leaves and stems are turning yellow from the bottom up. Even the leaves around the current fruit set. I am not sure what's going on there but I did ad some home made compost to the pot a couple weeks ago. Maybe it's off balance now? I added the same compost to my peppers and squash and they are all doing great, minus a pepper blossom turning yellow and dropping here and there. Just one or two, I'm sure that's normal. They're still producing and the foliage looks fine. I put just a sprinkle of tomato fertilizer in the pot and I'll water that in tomorrow morning as well. One last thought for the night. When I sprinkled the fertilizer around the tomatoes in the garden earlier, I noticed within minutes, ants all over the surface carrying away bits of the fertilizer. Anyone else ever seen that? Should that concern me? I just kinda thought it was neat. Jennifer

Thank you digdirt2! Your advice has been invaluable! I did see a few bugs on some leaves, but nothing that seemed like an epidemic, but I have no idea how many mites it would take to start damage if it were from them. I first noticed this last Friday and they seemed to be better the next afternoon. Then I noticed it again today. Some varieties seem more affected than others. Purple Russian seemed to be the most affected. We have had a very warm spring and I've had difficulty trying to find the right level of watering. Then it kills me since some seem to dry out faster than others, and trying to spot water that many seems like an effort in futility with this may starts! This is my first year growing starts for sale (I have a booth at a local farmers market) and I love what I'm doing, but I do have some perfectionist tendencies and can't stand seeing any plants having issues. It does seem to affect the lower older leaves first, and I don't see any discoloration. So perhaps what the article stated "The disorder is also attributed in some areas to excess soil moisture coupled with prolonged high air temperatures." is my issue. Slightly too much water, and high air temps. "Rolled leaves become rough and leathery but are otherwise normal in size and appearance. There is no discoloration of leaf veins associated with this condition." The leaves do feel rough and leathery, and all else seems to match what this article says. Again, many thanks!