Hey all,
  I have a tree (LSU Scott's Black) that is showing what looks like rust forming at the underside of some of the leaves where the stem meets the leaf.  Does it seem odd for this to be happening indoors in NJ in March?  Here are some related facts:
  I brought the tree inside last November.  It was about 3' tall and had lost all but three leaves on a low branch, and those leaves were still in relatively good shape (starting to brown up a bit at the ends).  I put it near a window to just to let it get that last bit of energy stored before going dormant.  Lo and behold, it never dropped those leaves.  Then it took me by surprise in mid December and had some bud break and started putting out growth from some of the branches.  Before I knew it, it just took off growing through December, January and February. It put on over a foot of growth on some branches and was looking very fine.
  About 1 weeks ago I noticed what looked like rust on some of the leaves.  I went away for a week on business.  When I got back the rust was stronger, and some of the leaves looked a bit shriveled...but near the base rather than at the ends.
  This tree has been in the house all winter.  Its leaves have never gotten wet.  I would be surprised if the humidity ever went significantly above 50% this winter.
  I guess there could have been rust on the old leaves.  And there could have been rust in the potting medium.  But would you think it would spread under these conditions?
Jim
PS -- I know...pictures, pictures...

I know I will be spraying all my fruit trees with a Copper Bordeaux spray come winter.

Hi needaclone,
Do you have artificial lights ?
Didn't the leaves get burned from the lights ? and you think that it is rust perhaps ?

I just had the same situation with very small trees that never dropped their leaves this winter. I removed all the leaves that had been there and the new leaves coming are showing no signs. It may just be the end of the life cycle for those leaves.

Javajunkie, what you say makes sense to me.  Rust is not an issue here in dry So CA, but there was an appearance of rusty leaves on the only tree that didn't go dormant.  Big old leaves looking pretty nasty.  I think you are right.  End of the life cycle for those leaves.  I did pull them all off, like you and new leaves are nice and green.  It didn't occur to me that those leaves just needed to go.

Suzi

i make extra effort to clean up around the tree all the time. in 2012 had to lot of rust on the leaves towards the middle of summer. last yr after i went about picking up old leaves, it was little better. but it was wet and cold autumn. 

There are only 2 leaves that remain from last season.  They look old and beat up and ready to be cut off.  There's no obvious sign of rust on them...they just look like they've lived a long, hard life and are ready to go.
All the other leaves (the ones with what looks like rust and a bit of drying) are "new" -- i..e freshly grown on green wood since December or more recently.
They are not under artificial light.  They are in a bathroom whose shower does not get used, which is why I don't think it is a humidity issue.  I've got hygrometers in different parts of the house, one nearby, and only now is it starting to pop just above 50% occasionally.  It is right in front of a south-facing window that gets light from morning to early afternoon.  There is also an east facing window and a skylight, so it also gets a lot of bright ambient light from some other directions. 
  All the leaves grew under these lighting conditions, so I would think they'd be acclimated.
  I gave it a drink before I left on a 5-day trip, but none of the leaves were droopy.  (I have tried not to overwater it, and it usually slumps a bit to tell me it is thirsty.)
  I guess there is a chance I temporarily overwatered it (e.g. just before I left and also sometime in the week leading up to that.)
  I'll get pictures tonight, but it looks like rust.  Again, these are relatively new leaves in dry conditions...so it is odd.
Jim