
Learn more about Johnson Grass
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. This grass is a serious potential threat in many old fields where succession to forest communities is desired.
To eradicate Johnson grass, control measures must be thorough. Various cultural practices and chemical herbicides will effectively control germinating seed, seedlings, and established plants. Objectives of a good control program include:
Johnson grass does not infest areas of high natural quality heavily except for the naturally disturbed environment such as along river banks 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 percent Roundup (a formulation of glyphosate). Best results are obtained when glyphosate is applied to plants that are 18 inches tall to early flowering stage.
During this period the herbicide will be most effectively translocated to the roots and rhizomes. Care should be taken to avoid contacting non-target 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.
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 percent 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 re-invasion.
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. six times at two-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 percent Roundup on foliage using a tractor and power sprayer provides effective control.
Cutting and removal of seed heads during early July and then spot application of 2 percent Roundup to the foliage usually will be effective if continued for three to four years.
Preferred treatment is the same as given above for high-quality areas. Another treatment is spot application of 2 percent Roundup to eliminate invading individuals the first year and to eliminate all surrounding seed sources.
The following practices should be avoided: