You don't give a lot of information.

Like:  where are you at? 

what crops are you talking about spraying?  or are they in a non-crop area?

Here, i would expect that pigweed would be mature, seeds would be set.  So, here, you would probably be wasting your time to be spraying now.  Pigweed are annuals, and they will come from seed each year.  However, maybe where you are at, the pigweed have not yet set seed, or the seed are immature.  If so, spraying now might help reduce seed set for next year.  But *here* you would be wasting your time to spray now.

Care to elaborate with more detail?