Is it better to kill wild violets in May with Weed B Gone or in August with Roundup? Grass will be planted in early September. Weed B Gone can't be used when daytime temperatures are over 85 so it's now or October. How effective would Roundup be in mid to late August when the violets are not actively growing? It would seem to make sense to kill them before planting grass. But if I kill them now, it's three months before I can plant. The violets have completely taken over several areas.