The product you mentioned is a single application program for your lawn for the season. Application of this product for pre-emergence must occur before the germination and emergence of Crabgrass and other grasses/weeds. The duration of the residual weed control will be directly related to the amount of product applied and conditions in your area. The product label which will give you specific usage rates and instructions for your lawn, can be found under the Description area on our website here: http://www.domyownpestcontrol.com/fertilome-proturf-weedout-lawn-fertilizer-plus-crabgrass-preventer-2504-p-2008.html