Best Management Practices:
Dallisgrass is a perennial, warm season grass with short thick rhizomes. This means that it grows primarily from March to November and comes back from its root system each year, as well as from seed. A good identification characteristic is the seed head formation (3 to 7 branches with spikelets arranged in four rows).
Controlling dallisgrass is no easy chore but control can be accomplished. Unfortunately, pre-emergent herbicides alone will not control this perennial weed. Remember, this plant comes back from its roots each year, so it will take both pre-emergent and post-emergent herbicides to take out dallisgrass from your lawn. Pre-emergent herbicides kill germinating seeds while post-emergent herbicides only control weeds that are already actively growing.
Certainty is one of the best post-emergent products on the market used to control dallisgrass. It works very well if used in the correct manner. It will normally take at least two applications 10 to 14 days apart to obtain excellent control. Also, the weed needs to be actively growing (May to August).
Unfortunately there are no post-emergent herbicides that are labeled for controlling dallisgrass in St. Augustinegrass. The only solution is to do one or a combination of the following: dig out the dallisgrass by hand, use pre-emergent herbicides. One can also spot spray with a non-selective herbicide like Roundup (Glyphosate). If you do decide to spot spray, you can expect at least some damage to the surrounding St. Augustinegrass unless you are extremely careful not to get any on your turf. So make sure there is no wind to avoid drift and set your sprayer to where the droplet size is much larger (not a fine mist).
Best Management Practices courtesy of:
Bes-Tex Supply, LLC P.O. Box 664 San Angelo, Texas 76902 Ph. 325-653-1300