There is little you can do at this point in the growing cycle to control weeds in an asparagus patch other than hand-pull them, Martha, unless you want to go out and hand-paint the clover leaves with an herbicide containing glyphosate (you do not want to spray anything for fear of getting it on the asparagus). You can mulch and use a pre-emergent herbicide in the spring, and there are other options available for fall, both of which you will find here:
Please note the caveat at the end of the article and disregard the advice of anyone who tells you to put salt on your asparagus patch.
Boy the rain we have had here has really made it difficult to control weeds. We may find ourselves sitting in the mud later this morning pulling up some weeds. We have got to get out that crab grass before it reaches my sod!