For myself, in San Antonio, it seemed to keep the crabgrass at bay from
my st. augustine. Dunno if it was just placebo affect, but my great
aunt swears by it.

You could get some ordinary corn meal. Then blindfold yourself, and
also blindfold your entire lawn. Then spread the cornmeal on half of
your lawn (randomly selected) and the corn gluten on the other half.

Voila! A Double-Blind study that should eliminate the placebo
problem.

Happy to be of help.

vince norris