Johnsongrass continues to spread into new areas in northwest Missouri. This weed is a perennial grass weed that spreads by seeds and rhizomes. Johnsongrass is listed as a noxious weed by the Missouri Department of Agriculture. More information about noxious weed law can be found at https://agriculture.mo.gov/plants/pdf/missouri-noxious-weed-law.pdf.

A single plant of johnsongrass may produce more than 80,000 seeds in a single growing season and more than 275 feet of rhizomes. Seeds can remain dormant and produce plants for several years. Seed may remain viable in the soil for more than 10 years.

Prevention is the best way of avoiding johnsongrass movement into new areas and fields. Typically, johnsongrass has been found in soybean and corn fields and field borders. Now it is making its way into cool season grass pastures.

In pastures, methods of control are limited. Spot herbicide treatments that translocate to control roots are critical for control. If left untreated, the johnsongrass will take over the cool season grass pasture.

In row crops, control plants before harvest to reduce rhizome and seed production in following rotational crops. Always follow herbicide label directions. Control will take sustained effort and a focus on marginal field areas such as ditch banks.

For more information, contact Wayne Flanary, Field Specialist in Agronomy, at 816-279-1691, University of Missouri Extension.