One and only one leaf on one of my EE's has what looks to be rust? The whole leaf is speckled and just keeps getting worse.

Can I cut the affected leaf off, should I try to treat it somehow?

Here is a pic:

It looks better in the pic than it actually is.

I have 2 giant EE's in a half barrel. Full sun. Soil is a mix of composted manure, compost and clay soil. Had alot of surface roots couple weeks ago, so I threw about 2" of sand on top. Now the roots are actually growing through the cracks between the slats at the top of the barrel. Also maybe I should mention that the barrel is sealed up to about 3/4 of the way up to hold water, so the soil is constantly moist.

O and today I noticed the bottom right edge of the leaf is starting to dry, brown and curl, almost like its burned from the sun?

Other than this one leaf it seems perfectly heathly as does the 2nd EE in the barrel.

TIA for any help,

Daniella