Nimblewill
Click for larger image Nimblewill (dull, blue-green patch) in lawn

Nimblewill, Muhlenbergia schreberi, is a warm-season perennial grass, which forms dense mats one or more feet in diameter in sun or shade. Patches look fuzzy, somewhat like a scouring pad, with a dull, blue-green tinge making them quite noticeable against the greener lawn grasses. Its stoloniferous growth pattern makes it resemble creeping bentgrass and Bermuda grass. Because it is a warm-season grass, patches of nimblewill appear as brown, dead spots early in the year and can be confused with actual dead spots. During the growing season its blue-green color and "fuzzy" faded appearance helps to differentiate it from other grasses. It is weakly attached to its roots and pulls up easily. It grows well in either sun or shade and often invades shady areas of turf where other more desirable grasses find it difficult to grow.

Symptoms and Diagnosis

Nimblewill has thin flat leaves with four veins on the upper surface; its leaves are usually less than 2 inches long and are blue-green. Leaves are rolled in the bud with a very short membranous ligule and only a few hairs near the ligule. The hard thin stems begin growing upright but later often lie flat on the ground near the base and become upright farther up the stem. It can be confused with creeping bentgrass which is finer in texture with narrow green leaves, a large, pointed ligule and no hairs around the ligule. Another look-a-like is Bermuda grass, which can be distinguished by its fringed ligule of fringed hairs.

Life Cycle

Nimblewill is a warm-season perennial grass, which flowers from August to October. It turns brown at the first frost and is very slow to green up in the spring. It spreads by seeds and spreading stems.

Integrated Pest Management Strategies

1. Maintenance. Maintain a dense, healthy lawn through proper turf selection, establishment, and maintenance. Improve soil drainage, reduce shade and increase air movement.

2. Chemical control. Presently only one herbicide available to homeowners, Tenacity (active ingredient mesotrione), provides selective control of nimblewill in cool-season lawns such as Kentucky bluegrass, tall fescue, fine fescues and perennial ryegrass. Application rates can vary so follow label directions. It is not approved for use on warm-season grasses such as zoysia grass. Several applications are needed for good control and a non-ionic surfactant should be added to the mix. Nimblewill will become bleached and white as it dies.

A cheaper control method is to apply a non-selective, post-emergent herbicide such as glyphosate (Roundup) to patches of nimblewill and then replant the areas. Apply the herbicide when the nimblewill is actively growing during the summer. Applying in late autumn to early spring when it is dormant will not provide control. Glyphosate, being a non-selective herbicide, will kill desirable lawn grasses as well.

3. Watering. Improve drainage as nimblewill thrives in poorly drained moist soil.

Organic Strategies

Strategies 1 and 4 are strictly organic approaches.

More images

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Lawn grass thins out in shade allowing weeds like violets and nimblewill to take over.
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Nimblewill turning white after an application of the herbicide Tenacity.

Pests and Problems

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