Help for Saint Augustine Grass Problems with Weeds
- St. Augustine grass commonly invades fescue, annual bluegrass and crabgrass. Gardeners can eradicate these grasses from the lawn by applying pre-emergent herbicide, according to Texas A&M University. Pre-emergent herbicide inhibits grass seed's ability to germinate; thus, it is ineffective on seeds that are already germinating or on existing weeds. Apply pre-emergent herbicide in the spring before the soil warms up to 60 degrees Fahrenheit to prevent missing your opportunity to prevent seed germination. Water the pre-emergent herbicide into the soil.
- Post-emergent herbicide must be selective in areas where weeds are growing within your St. Augustine grass. Gardeners must use a post-emergent herbicide that is chemically formulated to kill the weeds without harming the St. Augustine grass. Also, a post-emergent herbicide for broad-leafed weeds must be used within the yard. Refrain from mowing for two days before and after you apply you post-emergent herbicide, so that the chemicals have enough leaf surface to absorb into the plant.
- Spray a non-selective herbicide that contains glyphosate onto weeds growing near non-target plants, such as in the driveway or on the sidewalk. Glyphosate becomes almost completely inert when it contacts the soil, so you don't have to worry about runoff. To be safe, place plastic on top of St. Augustine grass or other ornamental plants to protect them from the spray. Spray your non-selective herbicide on a dry, wind-free day.
- Weeds can be prevented with proper cultural practices such as mowing. Keep your St. Augustine grass 2 1/2 inches tall, according to Texas A&M University. Mowing any lower can put stress on your St. Augustine grass. Avoid taking off more than one-third of the grass blade at a time to prevent causing a weak root system. Weak root systems can lead to thinning grass or bare areas where weeds can take advantage of the lack of competition.