If you haven't already done your pre-emergent herbicide treatments in your asparagus, it's getting that time!  Rutgers University in New Jersey recommends 2.5 lb Solicam DF plus 1-2 lbs Karmex DF (do not apply more than 3  pounds per season), 14 days prior to spear emergence (that's the pre-harvest interval) which means applications need to be going out very soon if not immediately (for beds that are at least 1 year old)!  This tank mix works on a wide range of pre-emergent broadleaves and grass weeds and is relatively safe to the asparagus.  Both of these materials will not work on already growing weeds and also work better if moisture is received soon after application.  If weeds are present, the addition of Gramoxone or other paraquat containing material will help control those weeds already established. The addition of Calisto at 3.0 ozs per acre can also improve residual and Common Larmbsquarter and horseweed (marestail or stickweed) control.