Corn gluten meal MAY reduce reproduction by seed by a maxiumum of 50%. For a plant as tough as dalligrass, the percentage is probably much lower.
Are you SURE you don't want to use a glyphosate and kill it effectively and quickly? Glyphosates do NOT stay in the soil. They quickly break down into harmless chemical elements.
I can't imagine putting black plastic on a lawn for several weeks. But that is an aesthetic decision.
BTW, you didn't say what your turf grass is.

Just curious about a couple of things - 1. did you try a method to rid your lawn of the dallisgrass? 2. if so, did it work and what did you try?

I also have a huge dallisgrass problem and don't know how to deal with it. Pulling it by hand is just so overwhelming. Will the Glyphosates harm the tree it's near and/or my kiddos? How long does it stick around? Our turf grass is Bermuda.
any help would be greatly appreciated.
thanks, Lara

Glyphosate will not affect the trees in the area since once it hits soil it is completely inactivated as a herbicide. To act herbicidally, it must be applied to green plant tissue. It will not affect seeds in the soil. If used as directed it will not present any risk to people and the product will eventually be broken down completely by microorganisms in the soil. How long this takes is dependent on soil moisture and temperature, with half lives varying from a few weeks to months in temperate climates.