Specialty Gardening: cuc diagnosis?, 1 by michaelangelo

michaelangelo wrote:
I grew cucs very successfully last summer in this large 20 gal tub. As you can see in the photo, one of the leaves has developed an odd coloration. Too much water?... root rot?...in too big a container too soon?... not enough fertilizer? I'm hoping this is a problem I can catch and fix early before my plant dies. (The actual color of the discoloration is sort of a tan.) Thanks in advance for ay suggestions you can give.