Roundup ONLY kills actively growing plants. It kills by stopping Photosynthesis - so if a plant is dormant (like sometimes in early spring) - it won't give you a good kill.If you spray a field with a lot of berry bushes - even if the grass is green& growing - if the blackberrys are stillnot budded yet - andif you spray - you mightkill the grass - AND make it a perfect area for the berry bushes to thrive.

Its the same with spraying a mowed field. If you mow - you should wait till it starts to "green up" before spraying with Glyphosate.

I like to wait until Mid May in NY to spray.

FH