War on Weeds—weeds are everybody’s problem

  Johnsongrass (Sorghum halepense) is an invasive perennial grass that is native to the Mediterranean area. It was introduced to the United States as a forage crop but has proved to be a competitive weed. It invades pastures, ditch banks, and cultivated fields. Johnsongrass spreads by seed and rhizomes, allowing it to invade new areas quickly. 

Johnsongrass can grow up to 6 feet tall, has an extensive fibrous root system, and it produces rhizomes (underground stems) that aid in its spread. Leaves are flat, broad, and smooth with a prominent white mid-vein. Auricles are not present while ligules are membranous and have fringed hairs at the top. Johnsongrass has large, open panicles that form in a pyramid shape and contain red to purple-colored spikelets. The seeds are oval and reddish-brown in color. One plant can produce up to 80,000 seeds in a growing season and seeds can remain viable in the soil for up to 10 years. Seeds are dispersed by humans, animals, wind, and water.  

Integrated Pest Management (IPM) Options: 

• Prevention— Learn to identify this plant. Never transport unknown plant material.  
• Mechanical— Tillage is usually not a recommended method of control for weeds that spread from rhizomes, but it can be effective if used with chemical control options. 
• Cultural— Mowing or grazing closely for multiple years can weaken Johnsongrass stands making other forms of control more effective. Establishing a healthy stand of desirable plants is extremely important.      
• Chemical—Visit the Pacific Northwest Weed Management Handbook website (https://pnwhandbooks.org/weed), and search “Johnsongrass”. Always read and follow herbicide label directions.

Justin Hatch, University of Idaho Extension Agriculture Educator in Caribou and Bear Lake Counties. 208-547-3205 [email protected]