When is the best time in spring to use a lawn fertilizer with a pre-emergent herbicide?

Question:

I would like to know the best time in spring to use a lawn fertilizer with a pre-emergent herbicide?

Answer:

Dave Fuller, Agriculture and Non-timber Forest Products Professional 

Pre-emergent lawn herbicides need to he applied before the soil temperatures reach a point where the weed seeds begin germinating. A great indicator for timing is before the forsythias bloom, or in your neck of the woods, probably now. Also, don’t disturb the soil after the application as with raking, as this may disrupt the efficacy of the herbicide