It works by soaking up the excess water that’s on the plant, drying out the mold/bacteria. I was told this by an old-timer in another gardening group. I tried it and it worked. The only other thing corn meal can do is kill off ants. It makes them explode like rice does to birds. Ants are to aphids as dairy farmers are to cows. Without the ants to protect them, the aphids find another home.