Member of the Month: Dec 2016
Good Job catching it
Bud rot. Growing in corn is good idea to hide plants but not so good for your plant to get proper ventilation. Humdity and temperature contribute to this crap. If you grow in corn again, uproot nearby stalks so some air can circulate in there. I also noticed all the mold on the corn and the leaves of your cannabis looked like it also had some powdery mildew which could have been your first alert to a problem.
Since you've already harvested I think all you can do now is trim all the discolored areas out. What's left of the bud might be sprayed with hydrogen peroxide (H2O2) and washed in baking soda/lemon juice and clear water. You could spray with outside water hose. Then you need to hang it for drying making sure you have them well ventilated by a fan moving the air around.
The mold (botrytis cinerea or grey mold) will be harmful to your lungs if not all removed.
Seems a shame.