The Arrest will not hurt most of the seed/plants by whitetail institute. Go to there web page and read up on it. If it is that thick I would mow if down than rack it up, or it will clog your tiller up. Then I would till it this fall so the roots can start to decompose <-(Spell). Make a compost out of all that grass to put back on the food plot latter on. I would still spay it with the Arrest.