Thursday, March 26, 2015

Weed of the month for March 2015 is Tall Fescue

Tall Fescue  

Biology: Tall Fescue (Festuca arundinacea) is perennial grass that can be both desirable as a lawn species when using improved cultivars or undesirable when forage-type (wide-bladed) tall fescue plants a contaminant other primary species in a lawn.

For all of you nerds out there like me, you might be interested in know that there has been much recent debate about the scientific name of tall fescue. While tall fescue has used the above scientific name consistently for over 60 years, it is now being classified by scientists formally as Schedonorus arundinaceus (Schreb.) Dumort. (also = Lolium arundinaceum (Schreb.) S.J. Darbyshire; formerly = Festuca arundinacea Schreb.). I know, very confusing even for me. Remember that there are many grasses called “fescues”. I wrote about this in a previous turf tip that I would encourage you to read (click here).

Identification: Tall fescue is a coarse-textured (wide-bladed), bunch-type grass. Improvements in tall fescue leaf texture have resulted in more fine-bladed varieties/cultivars that have helped to increase the turf quality and use of this drought-tolerant turf in Indiana. We often recommend improved turf-type varieties of tall fescue as the primary species for lawns, but older, wider-bladed, forage-type varieties of tall fescue such as Kentucky 31 (KY-31) still exist, and can be problematic weeds in lawns. This forage-type tall fescue can be easily spotted in lawns in early spring when they green-up faster than Kentucky bluegrass and by its bunch-type growth habit, which results in a clump of turf when present as a weed. Also, forage-type tall fescue can be easily spotted in lawns during drought as tall fescue stays green and actively growing during drought whereas Kentucky bluegrass will often enter a drought-induced summer dormancy.  

Kentucky 31 (KY-31) tall fescue makes a poor lawn.

Improved "turf-type" tall fescue

Sometimes tall fescue blends well into your lawn. Notice tall fescue clump in center of photo.

Weedy, forage tall fescue clumps are easily visible in Kentucky bluegrass turf in early spring.

Tall fescue in bermudagrass turf in the spring during green-up.

Tall fescue (green clumps) in a Kentucky bluegrass turf during a summer drought.

Tall fescue will often lack a ligule or possibly have a short membranous ligule. 

A very short ligule is barely visible.

Auricles are usually short and blunt but some can also be classified as short-clasping meaning that the auricle may wrap-around the stem but may not fully clasp or cross one another. You may also see small hairs protruding from the auricle. 

See the short auricle and small hairs?

The vernation (how the leaf is oriented inside the stem) is rolled on tall fescue and the collar is conspicuous (obvious) and usually wide.

Broad collar is easily visible.

Broad collar is easily visible.

The leaf blade is wide but variable in length with a pointed leaf tip. In some cases you can actually feel little barbs along the leaf margin when you run your fingers from the leaf tip down the leaf blade.One last helpful identification is the prominent veins in tall fescue compared to Kentucky bluegrass (only midrib is clearly visible).

For more on tall fescue identification, see this page in our turfgrass identification tool (click here, requires flash player).

Cultural control: When there are few weedy patches of bunch-type grasses like tall fescue, it is best to cut them out with a shovel or knife. Be sure to cut down a couple of inches into the soil to get all the stems. Refill the holes with soil and seed immediately with the desirable turf species similar to the existing turf.

Biological control: None known.

Chemical control: If the area has a large number of tall fescue plants, chemical control will be more efficient. A nonselective herbicide such as glyphosate (Roundup and others) can be spot-applied. These herbicides will also kill the surrounding desired turf species, so be careful to treat only the clump of tall fescue. Two applications may be needed for complete control and the area should be reseeded 7 to 14-days after the final application. Thoroughly rake the area to be seeded to remove dead plant material and ensure good seed-soil contact. For more information about complete renovation, refer to Turfgrass Renovation (Purdue Extension publication AY-13-W).

Chlorsulfuron (Corsair) was a selective herbicide registered for the control of tall fescue in many turf species. Some quantities of Corsair (labeled for most major turf areas) may still exist but this herbicide is no longer sold. Telar XP and Chlorsulfuron 75DF contain the same ingredient as Corsiar and can be used on turf in industrial sites and roadsides but not in managed turf areas like golf courses, lawns, and athletic fields. Spot apply chlorsulfuron according to label instructions. The tall fescue will slowly thin and die, allowing the desired species to fill in. Reseeding should not be needed if Kentucky bluegrass is present. Chlorsulfuron will kill perennial ryegrass, so do not apply it to perennial ryegrass.

To control tall fescue in warm-season lawns and athletic fields, apply a nonselective herbicide like glyphosate in late winter while bermudagrass is dormant. Alternatively, many sulfonylurea herbicides are labeled for the selective removal of cool-season grasses such as tall fescue from bermudagrass and zoysiagrass.

For more information on weed control, search this blog and check out our Turfgrass Weed Control for Professionals Publication.

For archives of past weed of the month postings, visit our Weed of the Month Archive.

Aaron Patton, Turfgrass Extension Specialist


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