I’ve discussed this question many times in past articles.  You can throw in a pyrethroid insecticide for $2-3, so why wouldn’t you?  Sometimes you may actually need it, but at other times, this can actually hurt more than it helps.  My experience has been the most economical choice is to spend more time scouting and less time spraying blindly. My counterpart, Dr. Angus Catchot at Mississippi State University, wrote an article last week that is definitely worth reading.

http://www.mississippi-crops.com/2013/07/02/fungicide-time-for-soybeans-the-insecticide-add-on-dilemma/ (Dr. Angus Catchot)