Q: Is it OK to put out Weed B Gon to kill weeds before I plant fescue seed?
A: No – it’s not OK.
Weed expert Dr Mark Czarnota says
“This class of herbicide has preemergence activity on most plants (from seed) – even though most people think that they are only postemergent herbicides.
If you are in to herbicide history, before preemergent herbicides, 2,4-D / dicamba applications were targeted to try and kill germinating annual grasses (when the forthysia shrubs were blooming).
All of the herbicides in these classes (phenoxy, benzoic acid, pyric acids, etc.) have different lengths of time that they are active in the soil and cause preemergent activity, thus different lengths of time before you can re-seed / plant back. “