The Ob-noxious Johnson Grass

Johnson Grass, Sorghum halepense, is a tall grass that is native to the Mediterranean.  In many regions of the world, including Kansas, it is considered a noxious weed.  This essentially means that it is invasive to Kansas and that it is harmful to both animals and other plants in the environment.  It is difficult to keep from spreading, and is especially hard to eradicate a population of this grass species once established.

Johnson grass is sturdy, rough, and can grow as tall as eight feet tall.  Its leaves can be anywhere from six to twenty inches and have a white vein along their midline.  Johnson grass also has reddish-brown seeds that are around one-eighth inch long.  These qualities help identify it from similar native species of grasses in Kansas such as eastern gamagrass, switchgrass, big bluestem, and indiangrass.  The plant flourishes in numbers.  This fact is essentially due to its system of reproduction.  Its rhizomes allow it to develop many different individual plants underground.  Many shoots above ground can pop up above ground, originating from the same root.  This makes it hard to get rid of this noxious weed.

Driving on the road, looking out of a window into an open field, or just walking along a path in nature all result in one inevitable sight: Johnson grass.  The costly, tedious process of removing this unsettling thought is often deemed futile.  The main ways it can be removed are mechanical and chemical, although neither are guaranteed effective.  The mechanical means involve hand-pulling, hoeing, mowing, plowing, disking, and cultivating.  Hand-pulling is a method used when attempting to control just a small group of plants because it cannot be used on a large scale effectively.  It is very important when using this method to dig up all of the rhizome, as just small pieces of the root can result in propagation of another plant.  It is the most thorough of any procedure but also takes the most time.  Mowing can be an efficient process but it only controls the seeds, and this only helps for a short time before the plant regrows.  Only controlling the top half of the plant also does not account for the rhizomes through which the plant also spreads.  Tilling into the ground is commonly the most effective, large scale solution to mechanical Johnson grass removal because it disrupts both processes of Johnson grass dispersion.  Chemical removal of Johnson grass most commonly comes in the form of herbicides.  This grass is so durable that only the strongest of chemicals can effectively kill it.  These inhibit the process of photosynthesis so entirely that even the rhizomes eventually wither and die due to a lack of nutrients.  Regrettably, however, the strength of these herbicides kill everything they touch.  Selective herbicides exist that only will affect Johnson grass, although they are of the most expensive on the market.  It is not hard to understand, in this sense, why local governments do not invest much money in eliminating Johnson grass.  Unfortunately, this only further contributes to the spread of Johnson grass.

About Mr. Mohn

Biology Teacher

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