I purchased the Preen for the garden this year. So far, we have almost no grass coming up, so I have not used the Preen.
In the 1970's I worked on a farm where we used Preen (Treflan) on over 1000 acres of soybeans to control Johnson grass and other weeds.
I learned a lot putting down that much of that chemical.
1) if you miss a spot, expect grass to grow there - we were spraying it as a liquid and overspray did not move the control area very far - so, put the Preen where you want control.
2) double tilling is a MUST! The control ranges from 0% to 50% if you single till in the product. I can not understand how the product knows if it was single tilled!!
I put the chemical down, and disked it in. Double-disking 1000 acres is a LOT of disking, even using a 22 foot wide disk!!
My brother-in-law was on me like scum on a pond every time he saw a spot I had missed!!