Johnson grass (Sorghum halenense) is a perennial grass weed that reduces crop yield in cotton, grain, soybeans and other forages. According to the U.S. National Forest Service, the troublesome grass is among the top 10 noxious weeds in the world because of its negative ecological effects. Although chemical methods of killing the grass exist, instead consider environmentally safe and organic alternatives that do not have a harmful impact on the soil.
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The U.S. Department of Agriculture suggests hand-pulling individual plants or small infestations of the grass. Pull out the complete plant along with the rhizomes because the smallest pieces can stimulate new growth. The best time to pull out grass plants is in early spring when the soil is moist and chances of rhizome breakage are minimal. Grasp the stem of the plant firmly in the middle and pull it so that it slides out of the soil. Loosen the soil with a hand trowel or moisten lightly if necessary to make sure the plant does not break. Collect dead plants in a bag and dispose of them.
Use newspapers to smother and kill unwanted Johnson grass in your yard. Mow the grass down as short as possible and discard clippings. Spread piles composed of eight to 10 sheets of black and white, nonglossy newspaper over the grass. Overlap edges of adjacent sheets by 3 to 4 inches to prevent sunlight, air or watering from reaching the grass below. Spread a 2- to 4-inch-thick layer of organic mulch such as wood chips over the sheets of newspaper to weigh them down and hold them in place. You also could sprinkle water over the chips to keep them from blowing away. This newspaper mulch kills unwanted Johnson grass in two to four weeks and begins to decompose in the soil, enriching it with beneficial organic matter.
Pour household white vinegar over Johnson grass for an inexpensive, effective means of killing it. Because the acetic acid in the vinegar burns the grass, check the percentage of the acid the particular brand of vinegar contains. The higher the acid content, the more effective it is in eradicating the weed. Apply vinegar in spring when the grass is young or during fall when it is building food reserves in its rhizomes. Spray vinegar directly over each grass plant, dousing it completely. Cover any desirable plants nearby with a cloth or tarp to protect them in case of accidental spray. Repeat application every other day until stubborn plants die.