Japanese stilt grass is now in the process of reseeding and will soon die with first frost. Any overseeding with rye or fescue will germinate and will get established through the fall . You will have to remove the stilt grass to allow the new seed to come in contact with the soil for a successful overseeding. In mid-March,apply a pre-emergent crabgrass preventer to prevent the stilt grass from germinating.
If the Japanese Stiltgrass seeds are not removed in the Fall, will their new growth crowd out the new growth and overseeding for Fescue and Rye grass in the Spring season?
This is why we recommend renovation and overseeding be done in the fall... there is less weed competition.
The application of a pre-emergent is done in the spring about the same time as the yellow forsythia bushes are blooming. Pre-emergents stop the germination of seeds, and if timed well, stop early weed seeds from germinating.