Nimblewill (Muhlenbergia schreberi ) is a warm-season perennial grass with a fine texture and a gray-green color. It spreads by stolons and forms a dense matt in cool-season lawns. It has a rolled vernation and a membranous ligule with jagged edges. It looks a little like creepting bentgrass, but it does not have a long membranous ligule that typifies bentgrass and has fine hairs around the collar. It forms a narrow spike-like panicle of seeds, with each seed having a fine awn (hair) at its tip (Figure 1).
It has been nearly impossible to control once it has become established in the lawn. It can be killed by nonselective herbicides, but it is also a good seed producer and it often returns from seed. It is a warm-season species and it looses its chlorophyll in the fall and takes on a bleached, straw-like appearance that makes it stand out in cool-season lawns. It is sometimes referred to as ‘wire grass’ in parts of the Midwest.
Tenacity (mesotrione), was released into the lawn care market in the spring of 2011. It had been available for a few years in the sports turf and golf markets. This material can selectively control nimblewill in Kentucky bluegrass turf. It is also labeled for the control of creeping bentgrass in Kentucky bluegrass and for the pre and postemergence control of crabgrass.
The pictures below are from the lawn of our "answer-line" person in the department, Richard Jauron. Richard gets a number of questions on nimblewill control and decided to do a test in his own lawn. These pictures are from the 5th of July, 2011. Richard will continue to update us on his experience with the material throughout the season. The material will turn susceptible weeds snow-white when it is first applied. It does take at least two applications for complete control of nimblewill, and may take more treatments. Remember too that nimblewill is a good seed producer. We will follow this through next season as well and not stop until control is complete.
Figure 1. Seed head of nimblewill with "awns".
Initial effect of tenacity on nimblewill in Richard's lawn. The white color is a typical response to this herbicide. Richard will repeat apply two weeks after the first application.