I live in southeast lower Michigan. I put down crabgrass preventative about 3 weeks ago (1st week of March). The instructions on the bag say not to seed for 6-8 weeks after applying the product. If I rake the lawn (so I can get some seed down) in the next couple of weeks, the crabgrass preventative will have been down for 5-6 weeks. Will that have been enough time for the prevetative to do it's business. Or will I have wasted time and money on the crabgrass preventative by raking the lawn after 5-6 weeks.