Spray off before or after plowing up a field

I took first cut of weeds off a very rough 10 acre field for a neighbour and they have asked me to plow and reseed for them, discing in fertilizer and lime as well.

One of the weeds is milkweed and I've found they pop up after plowing without much trouble.

Its had 2 weeks regrowth and I was getting ready to spray before plowing but thought I better ask if I should spray it off right before seeding instead?

Spray off before or after plowing up a field