Pre-emergent herbicides are only effective when applied before weeds sprout. In North Texas, it’s best to have them down before the 15th of March, and to absolutely have them down before March 22. After that time, weed seeds start to sprout, and each day forward means less and less control.
Get it down as soon as possible. Â Apply a second, lighter application of the herbicide three months later.
Ever since the herbicide MSMA was de-labelled for homeowner use, grassy weeds have been far more difficult to control in North Texas landscapes, particularly dallisgrass. Properly timed pre-emergent applications will prevent the problem. Don’t let the window of opportunity close before you do so.