Several postemergence options for annual bluegrass control exist for warm-season lawns, with bermudagrass and zoysiagrass having more control options than centipedegrass and St. Augustinegrass. Atrazine and Simazine formulations have existed for several decades and are labeled in all the listed warm-season turfgrasses. Generally, Atrazine is applied from November 15 to December 31, and Simazine is applied from November 15 to December 15. These herbicides provide preemergence and early postemergence control not only of annual bluegrass, but of many of the common winter annual broadleaf weeds as well. Perennial broadleaf weed control is usually weak. When applied early in November, Atrazine and Simazine can control small annual grass and broadleaf weeds with 1 lb ai/A. Rate increases up to 2 lb ai/A due to weed size are usually needed if applied to large weeds in December. Expect annual bluegrass to germinate and break through these herbicide treatments in March and April if the turfgrass stand is thin and spring rainfall is plentiful. To fight against this, Simazine can be applied at 1 lb ai/A from October 15 – 30 and then again from December 15 – 30.
In the early 2000’s, sulfonylurea herbicides such as Monument and Revolver were developed. These herbicides provide excellent postemergence annual bluegrass control and also control a fair amount of winter broadleaf weeds. Monument even controls perennial broadleaf weeds such as dandelion and white clover. Bermudagrass and zoysiagrass are tolerant to both herbicides. Unlike Atrazine and Simazine, annual bluegrass control is usually season-long, regardless of spring rainfall amounts. Apply Monument at 0.33 to 0.45 oz/A and Revolver at 17.4 fl oz/A.
Leon Warren and Dr. Fred Yelverton