Best time to put down weed 'n feed is in the fall, when the movement in the weeds is downward. I do crabgrass preventer/fertilizer in the spring, then weed 'n feed in the fall.
Maintenance Calendar for Indiana Lawns (AY-27-W)
The "Maintenance Calendar" provides seasonal lawn tips for cool season grasses. Three maintenance levels are established depending on the amount of money and time you are willing to invest. The calendar provides practices and notes on what you should do each month to ensure a healthy lawn.
www.turf.purdue.edu