Wirestem Muhly Biology and Management

Jerry Doll

Unlike most of our weeds, wirestem muhly [Muhlenbergia frondosa (Poir.) Fern.] is native to North America. It has generally remained on the fringe of agricultural systems, with rather limited appearances as a significant weed problem. The Muhlenbergia genus has over 50 species in the United States and this is the only one of agricultural significance. A 1960 article labeled wirestem muhly as "a new cornfield weed menace" (Scott and Slife, 1960) and alerted producers in the upper Midwest of the potential problem. Little changed for the next 20 years but since the mid 1980s, and especially in recent years, wirestem muhly has invaded new areas and has increased in frequency and density where it already existed.

The increased abundance of wirestem muhly is due to several factors, including less thorough tillage than previously, excellent control of other species, loss of diversity in crop rotations (especially less forages), and the production and spread of wirestem muhly seeds. The use of chisel plows and other toothed or tined tillage tools in stead of moldboard plows and disks may have increased the spread of wirestem muhly rhizomes and the adoption of no-till systems removes the suppressing effect that seedbed preparation has on wirestem muhly.

Description

Wirestem muhly can be easily confused with quackgrass because both are perennial grasses with rhizomes. However, as the following table illustrates, there are significant differences between them.

Biology and Ecology

Because wirestem muhly is a warm season species, growth starts later in the spring than for quackgrass and other cool season plants. In Ontario, Canada, 80% of the plants had emerged by June 4, 1984, (Swanton, 1984) and similar staggered and delayed emergence is seen in Wisconsin. Flowers do not appear until late July or August. Wirestem muhly rhizomes are very shallow and are new ones are not formed until July. Rhizomes are very shallow and wirestem muhly growth peaks in July and August. As Table 2 illustrates, once rhizome production begins, many new ones rapidly appear. Even more striking is the rate of inflorescence production. Single plants can form over 800 seed heads and counts taken in Wisconsin in 1995 found and average of 175 seeds per inflorescence (Doll, unpublished data). Thus a plant can produce 140,000 seeds per year.

Control

Cultural/preventative. The most important cultural practices to suppress wirestem muhly are (1) routine field scouting to detect infestations early, (2) crop rotations that include soybeans or alfalfa and (3) careful cleaning of tillage and grain harvest equipment. The fact that wirestem muhly is appearing in new fields is worrisome and early detection is the best way to minimize this because the problem can be managed before large areas are infested. A more diversified rotation is better than less diversified ones. The most difficult wirestem muhly management situation would be fields in continuous corn, especially in no-till fields where cultivation is seldom done.

Plants arising from seed are commonly seen in fields. Thus we know some infestations occur because wirestem muhly seeds arrive on combines or tillage equipment. Seedlings observed in the field in southern Wisconsin in 1995 had 4 to 5 leaf collars but had not formed rhizomes by late July. These plants had rhizomes at the end of August. If seedlings are killed mechanically or chemically before plants have rhizomes, the development of perennial clusters of wirestem muhly is prevented.

Mechanical. Wirestem muhly rhizomes are relatively shallow and if repeated, shallow tillage can be done at the right time, the results can be dramatic. Slife (1964) noted that vigorous tillage just as growth begins in the spring can be highly detrimental to wirestem muhly. Where planting can be delayed 10 to 20 days, this approach may be feasible. And perhaps wirestem muhly starts growing sooner than we realize. In two different years, spring non-moldboard plowing in heavily infested areas of fields decimated the wirestem muhly infestation to the point I was unable to conduct research on this weed (Doll, per. observation). Illinois' agronomists reported that periodic tillage after small grain harvest eliminated wirestem muhly in a single year (Scott and Slife 1960). They appropriately caution that this does not eradicate the problem as new plants may establish in fallowed fields from seed.

Rotary hoeing and cultivation will control wirestem muhly seedlings. Between row cultivation in corn and soybeans can be effective in reducing the density and vigor of wirestem muhly originating from rhizomes. Heavy duty cultivators with sweeps will be needed in most cases as the mass of rhizomes is less affected by cultivators with tines or narrow shovels.

Chemical. Wirestem muhly coming from seed is susceptible to many soil-applied herbicides including atrazine, cyanazine (Bladex), alachlor (Lasso, Partner and others), metolachlor (Dual), pendimethalin (Prowl), trifluralin (Treflan), and EPTC and safener (Eradicane) (Doll, 1986; Labovitch et al. 1984). Metribuzin (Sencor/Lexone) did not provide adequate control of wirestem muhly seedlings. These herbicides and other soil-active compounds have little effect on wirestem muhly coming from rhizomes. Glyphosate (Roundup) kills plants coming from seeds and the sulfonylureas (Accent and Beacon) stunted seedlings (Nandula et al. 1995).

Seedlings and established plants are controlled by the selective postemergence graminicides such as sethoxydim (Poast Plus), clethodim (Select), fluazifop (Fusilade) and quizalofop (Assure). Glyphosate is generally effective in killing treated plants but was the least treatment effective in no-till corn because it was applied pre-plant ahead of corn planting and considerable wirestem muhly emerged after the application (Nandula et al. 1995). In the greenhouse, Nandula et al. (1995) observed better control and more kill of rhizome buds with the 1x and 2x rates than half rates of these herbicides and when treated plants were 3 to 4 inches tall rather than 6 to 8 or 12 to 16 inches tall. When treated on June 4 to wirestem muhly 8 inches tall and with 8 leaves, control with glyphosate was excellent (Labovitch et al.1984)

While glyphosate and the selective graminicides kill emerged vegetation, reinfestation following application is more likely with wirestem than quackgrass. This may relate to the number of rhizome buds per unit area or to physiological differences between the warm and cool season grasses. The use of glyphosate in Roundup Ready crops may prove to be more effective than glyphosate applications in other settings because we can apply an effective rate at the ideal growth stage and have full season crop competition after treatment. Trials were started in 1995 to test the effectiveness of glyphosate in these conditions and results are very promising to date (Doll, 1995).

Doll (1995) observed better wirestem muhly control with earlier rather than later Accent application and there was little advantage to split or 2X applications (Table 4). Cultivation improved control significantly in June and July but there was no difference in end-of-season wirestem muhly pressure between cultivated and non-cultivated treatments.

References

Doll, J.D. 1995. Weed control results. (in preparation).

Doll, J.D., R.F. Klockow and J.L. Kutil. 1986. Control of quackgrass and wirestem muhly originating from seed. NCWCC Proc. 41:88-90.

Labovitch, L., R. Becker and J. Bohn. 1984. Wirestem muhly (Muhlengergia frondosa) - its biology and control. NCWCC Proc. 39:107.

Nandula, V.K., W.S. Curran, G.W. Roth, and N.L. Hartwig. 1995. Effectiveness of nicosulfuron and primisulfuron on wirestem muhly (Muhlengergia frondosa) in no-till corn. Weed Tech. 9:331-338.

Scott, W.O. and F.W. Slife. 1960. A new cornfield weed menace. Crops and Soils. June/July. pp. 19-20

Slife, F.W. 1960. Wirestem muhley, a new weed. NCWCC Proc. 19:57-58.

Swanton, C.J. 1984. Seasonal development and control of wirestem muhly. NCWCC Proc. 39:92.

1995