The T&G is a blend of seeds to my understanding. The grass you see growing is probably annual ryegrass, which is usually added to "green up" a food plot and make it look more appealing to consumers. It's also a lot cheaper than the other seed and will grow just about anywhere, which is really how the throw and grow works.
Post a picture if you can. If the grass is the only weed and it's ryegrass, it's actually part of the food plot. If there are other grasses in it as well, you can't really kill the weed grasses without also killing the ryegrass.
If you are just wanting to get rid of all of the grasses (including the ryegrass), you need a grass selective herbicide such as Clethodim. Clethodim works great on grasses but won't kill your broadleaf plants like radish, rape, clover, etc.
Killing off the ryegrass may leave too much bare dirt and allow the weed pressure to get even worse. If grasses make up the majority of the plot and you choose to spray with Clethodim, top seed with more broadleaf seeds such as a Clover. That will help cover the ground and keep the weeds at bay.
Sorry for the long response, but I know did plots can be frustrating. Hope that helps
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