Johnson grass is a tall, coarse, grass with stout rhizomes. It grows in dense clumps or nearly solid stands and can reach 8 feet (2.4 meters) in height. Leaves are smooth, 6-20 inches (15.2-50.8 cm) long, and have a white midvein. Stems are pink to rusty red near the base. Panicles are large, loosely branched, purplish, and hairy. Spikelets occur in pairs or threes and each has a conspicuous awn. Seeds are reddish-brown and nearly 1/8 inch (0.3 cm) long. Johnson grass should be accurately identified before attempting any control measures. If identification of the species is in doubt, the plant's identity should be confirmed by a knowledgeable individual and/or by consulting appropriate books.
Sorghum halepense with its white leaf vein, wide leaves, and reddish seedhead is distinguished from (1) eastern gamagrass (Tripsacum dactyloides), which has flowers in a spike rather than a loose panicle; (2) switchgrass (Panicum virgatum), which has no white vein and a greenish-yellow seedhead; 3) big bluestem (Andropogon gerardii) and Indiangrass (Sorghastrum nutans) which both have narrower leaves and usually lack a prominent vein.
Originally native to the Mediterranean, this grass now occurs in all warm-temperate regions of the world. It is widely distributed in tropical America, common in the southern U.S., and distributed throughout most of Illinois. It is particularly common in cultivated river bottoms in the southern 1/4 of the State, especially along the Mississippi, Ohio, and Cache River bottoms.
This species occurs in crop fields, pastures, abandoned fields, rights-of-way, forest edges, and along streambanks.
It thrives in open, disturbed, rich, bottom ground, particularly in cultivated fields.
Johnson grass is a very aggressive, perennial grass. It occurs in dense clumps that spread by seed and rhizomes to form nearly pure stands. The grass emerges late in spring and forms seed by July 1, reaching a height of 8 or more feet. Stems and leaves die back after the first frost, but the dead litter often covers the ground all winter. Rhizome cuttings commonly form new plants, making it very difficult to eradicate. It spreads rapidly and is not affected by many of the agricultural herbicides.
Effects Upon Natural Areas
Johnson grass invades riverbank communities and disturbed sites, particularly fallow fields and forest edges, where it crowds out native species and slows succession. It quickly dominates the herbaceous flora, reduces plant diversity, and is unsightly to observers. It occurs in disturbed parts of several natural areas such as Lower Cache, Horseshoe Lake, and Robeson Hills. This grass is a serious potential threat in many old fields where succession to forest communities is desired.
RECOMMENDED PRACTICES IN NATURAL COMMUNITIES OF HIGH QUALITY
Initial effort in areas of heavy infestation
Johnson grass does not infest areas of high natural quality heavily except for the naturally disturbed environment along river banks in southern Illinois where it is difficult to control selectively. Seed panicles should be cut and removed from the area where practical. Dense patches can be controlled by spraying the foliage with 2% Roundup (a formulation of glyphosphate) during June, just prior to seed maturity. Care should be taken to avoid contacting nontarget plants, since Roundup is a nonselective herbicide. Do not spray so heavily that herbicide drips off the target species. The herbicide should be applied while backing away from the area to avoid walking through wet herbicide. By law, herbicides may only be applied as per label instructions and by licensed herbicide applicators or operators when working on public properties.
Effort in areas of light infestation
Clumps and individual plants may be hand pulled during June, just after a rain when the ground is soft. All plant parts should be removed from the area. Broken stems and roots left in the ground should be dug up if only a small area is involved. It is more effective to spot-treat the individual plants with herbicide than to pull them, and large clumps can be sprayed with 2% Roundup using a hand sprayer or backpack sprayer. Herbicide treatment may need to be repeated for several years to ensure good control.
Preferred treatment is hand pulling of individual plants immediately upon discovery. All plant parts, including rhizomes, must be removed. It may be necessary to hand pull a population several times to obtain control. Surrounding seed sources should be eliminated where possible to prevent continual reinvasion.
RECOMMENDED PRACTICES ON BUFFER AND SEVERELY DISTURBED SITES
Initial effort in areas of heavy infestation
Repeated and close mowing kills Johnson grass seedlings, prevents seed production, and reduces rhizome growth and regrowth of shoots. Sites may be tilled where it is practical (e.g. abandoned cropland) and the exposed roots left to winter kill. Repeated tillage (e.g. 6 times at 2- week intervals during the growing season) prevents rhizome development and reduces Johnson grass populations. Limited early season tillage, however, encourages rhizome growth by spreading pieces of the rhizomes. In a monoculture, livestock may be used to eliminate the Johnson grass by grazing. Spraying 2% Roundup on foliage using a tractor and power sprayer provides effective control.
Effort in areas of light infestation
Cutting and removal of seed heads during early July and then spot application of 2% Roundup to the foliage usually will be effective if continued for 3-4 years.
Preferred treatment is same as given above for high-quality areas. Another treatment is spot application of 2% Roundup to eliminate invading individuals the first year and to eliminate all surrounding seed sources.
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Written for the Illinois Nature Preserves Commission by:
Natural Land Institute
Belknap, Illinois 62908