If you are referring to a crabgrass preemergent look for a preemergent that contains no fertilizer. See our website on crabgrass and look at Tips for Application regarding timing. Also, see our Turfgrass Maintenance Calendar for more information and see Spring Maintenance http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG112_Turfgrass_Main...
In general weed and feed products are not recommended because of the need to treat the entire yard and can contribute to overfertilizing your lawn. If you use it, follow label directions.
The best time to fertilize is in the fall not the spring. Excessive nitrogen applications in spring and summer increases disease problems and reduces stress tolerance.
Identify and spot treat broadleaf weeds with liquid broadleaf weed herbicides when they are actively growing. Follow label directions. http://extension.umd.edu/hgic/lawns/lawn-weed-identification