I have a mandarina (tangerine) in a pot on my roof, it has been fine until lately and the leaves started to curl on part of the branch. I don't see any bugs on the leaves they just curl up tightly. My handyman said he thought it was from ants, so I put some ant bait in the plant. It may have helped, the leaves don't seem to be curling in new places but I can't be sure. If it is better, it is a very slight change. I do think the ants that were always around the tree have moved on, I don't see them anymore.

Here's a picture. I'd love some ideas on what it could be.

According to this article you might have Citrus leaf miner.

http://uccemg.com/Edible_Plant...

That's a great article, thank you Hetty. I don't think it is the leaf miner as I didn't see trails and there isn't anything wrapped up in the leaves. However, farther down the page it states that leaves can curl inward from too much water and/or too much heat. We have had both this summer and the tree is in a large plastic barrel. It's quite possible that it was the heavy rains or the high heat and humidity. I will inspect the leaves again this evening when I'm back up on the roof and look for any trails but I'm pretty sure I would have seen them. I think I will have some more holes drilled on the sides of the barrel to improve the drainage and see how it goes.

2. Overwatering can cause leaves to curl or cup INWARD. Also, stress from very hot weather will cause leaf cupping

There is also a site that says potassium deficiency can cause similar leaf curl...especially in pots. Citrus are heavy feeders and if you have had lots of rain the nutrients may have been washed out. Your photo appears to show some yellowing in the mature leaves.

Good point as well. I am not very good about keeping to a fert schedule. Got to work on that too. It just seemed that it was doing fine and then I noticed it wasn't.

Jonna, ants don't do any damage to leaves generally (except those leaf-cutters!) but they are around if there is a sucking insect feeding on the leaves like aphids. They produce honeydew that the ants feed on.

The damage you see might be from aphids feeding a while back. They may have damaged the leaf structure when they were small so the leaves then curled up. The aphids can be long gone before you notice the damage.

Check the stems on the new growth for scale insects, too. They can cause deformity in the leaves the same way, as well.