I had exactly this problem with my plants a couple of weeks ago. The "lipped" leaves that were affected were all in the top 1/3rd of the plant and the worst affected leaves showed the rusting/brown areas you also mention.

I overhauled my DIY ventilation system and it pretty much stopped the problem in its tracks. Some of the leaves that were not too badly affected went back to normal. But the more heavily affected ones kept the lip around the edge.

There are some pics of the problem in my grow log.
PhatJay Reviewed by PhatJay on . I thought this was canoeing leaves Ok there's another post right here about canoeing leaves, but I didn't want to jack someone's thread. Besides, these leaves look different. Anyway, here is a picture. There's only one plant that is doing this out of a few.. I think a second one may've shown signs of it. It's not on all of the leaves but on several. Anyway, what in general are the causes of this? I thought my temps were ok, but I think it may be heat or light because it happened to the plant directly under the lamp Rating: 5