Upon which type of turf weed have preemergence herbicides typically been the most effective

The answer is annual grass weeds.
Preemergence herbicides typically been the most effective and preferred to control the annual grass weeds. Preemergence herbicides are widely used to control the weeds that are grown in lawns and if we use this herbicides many weeks before the germination of weeds, it will be very effective.

They went to leyden, holland