Should I Mow Crabgrass Before Spraying Weed Killer?

Question

Grass is long with weeds

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Answer 1

It is too late to spray when annual weeds have gone to seed. They are at the end of their life cycle so are dying anyway. The best you can do is mow the seed heads down (and catch them in a mower bag if possible) so there will be less seeds to germinate next year. Next spring, apply a pre-emergent crabgrass killer.

https://www.gardeningknowhow.com/plant-problems/weeds/crabgrass-control.htm