Issue 4, May 17, 2011

Selective Control for Nimblewill Now Available

For years, homeowners and professional lawncare applicators have had to rely on non-selective herbicides such as glyphosate when controlling nimblewill (Muhlenbergia schreberi) in residential lawns. Along with the nimblewill, non-target desirable plants such as bluegrass may be seriously injured or killed if contacted by glyphosate. Finally, we have a selective herbicide option for nimblewill.

Nimblewill is a warm-season perennial grass that is fairly common in Illinois. Typically found growing in shady or wet lawns and landscapes, it creeps by aboveground, horizontal stems that can root at the nodes and readily form patches. Its leaves are smooth, quite narrow, and short compared to many grass species. Individual plants look almost wiry. In fact, another name for this grass is wire-grass. A closer look at this plant will reveal a very short, membranous, toothed ligule. The leaves are rolled in the bud. The flower is a fine, slender panicle.

Nimblewill patches should have been obvious about a month ago when the cool-season grasses first started to green up. Nimblewill, being a warm season-grass, is much slower to green up and goes dormant earlier in the fall. While dormant, its appearance is that of very light tan-colored, "puffed up" patches (the patches look like buff-colored scouring pads). When nimblewill greens up to a grayish- or bluish-green in late spring, its appearance is more inconspicuous. In Illinois, Nimblewill may be confused with zoysiagrass which has a similar growth pattern. However, dormant zoysiagrass is more of a golden tan in color and unless planted it is very unlikely for it to suddenly appear as a weed.

For optimal control when using postemergent herbicides, nimblewill should be treated when it is young and actively growing in the late spring to early summer. It is recommended that you extend spray coverage beyond the immediate patches as creeping stems are prone to lurk in these areas. Stolons missed by applications may form subsequent patches.

Tenacity herbicide by Syngenta was approved this spring for use on most cool-season residential lawns. The active ingredient is mesotrione. It can control over 40 weed broadleaf and grass species including nutsedge. It can be used pre- or postemergence as well as at the time of seeding. Be sure to carefully read and follow all label directions. Spot treat patches of nimblewill with 2 to 3 applications (2 to 3 weeks apart) of Tenacity mixed with non-ionic surfactant. Avoid broadcast applications unless reseeding. Use a flat fan nozzle for even coverage. Affected plants will turn white as it is a bleaching herbicide. Whitening of turfgrass may last for several weeks which can be alarming to the uninformed. Be sure to prepare clients before using Tenacity on their lawn.

Tenacity is now available in 8 oz. bottles. Some professionals were leery about making the 1 gallon investment as the price is reportedly on the more expensive side. The use rate is quite low at 5 fl. oz. per acre. Additionally, Tenacity was granted "Reduced Risk" status by the EPA; compared to many registered herbicides it has favorable ecotoxicity and human health profiles.

Proper cultural practices can significantly aid in controlling lawn weeds. Be sure that watering, fertilizing, and cultivating are done properly and at the right time.

Many of our cool season turf grasses are dormant during hot summer days. Meanwhile, nimblewill is actively growing and enjoying the lack of competition. This unbalance can allow nimblewill to be a serious weed problem. Therefore, controlling patches while they are smaller is recommended. For up-to-date lawn weed control recommendations, consult with the University of Illinois Extension publication, "Illinois Commercial Landscape & Turfgrass Pest Management Handbook" as well as the "Home Yard and Garden Pest Guide." (Michelle Wiesbrook--adapted from an article by Michelle Wiesbrook & Tom Voigt)

Michelle Wiesbrook

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