I recently use Bayer Advanced Lawn Weed and Crabgrass killer on my very healthy lawn (perennial rye, tall fescue, red fescue, and bluegrass) About 3 days later there was a brown spot everywhere we used the product. I live in central PA and we have had lots of rain this year. The lawn was thick and healthy. The product said it was safe to use on lawns, but it turn mine brown. What caused this and how can I restore the green.