Turtles do love corn, and I read somewhere that in some places it's used as bait to catch wild ones.

I give my turts a few kernals now and then, especially since it's in season. It's not really good as a regular item in the diet. Interestingly, if you look at the ingredients in Mazuri, it's listed as a major one (which makes me question why Mazuri is rated so highly).
If I give tomato (which I also give occasionally), I give pieces that are firm and near to the skin, not the inside, which is more juicy and has the seeds.
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-