The fall is one of the best times to try and get the Annual Bluegrass under control. It is a clumping grass that only grows to about 5” or 6” tall, and puts out lots of small seed heads. The seed heads are a very light green color, could almost look whitish, next to the parent plant. Each one produces hundreds if not thousands of tiny seeds. You can use a ‘pre-emergent’ product that kills the seed as it germinates by applying it on the soil surface when they germinate. Scotts makes a lawn food with a pre-emergent weed control to take care of feeding and weed prevention in one application. You can also use ‘Green Light’ “Crabgrass Preventer”, which is sold mostly to control Crabgrass in lawns. If applied this time of the year it also controls the pesky Annual Bluegrass in and around ornamental trees and shrubs. There are two more products are very effective also. Pre-Seeder Weeder is a granular product that comes in a round shaker container. Another product that uses the same chemical is Weed Stopper II.
All of the above products do not kill already growing weed plants; they all kill the seeds as they germinate. So if you have weeds in the area, you need to pull, hoe, or cultivate those weed plants out before you apply any of these products.