• Cultivating switchgrass.old rail switch image by Alex White from Fotolia.com
  
  Herbicides are chemicals that are used for the control of weeds and other invasive plants. Herbicides vary in their effectiveness, levels of safety and methods of application. Switchgrass or Panicum virgatum is a warm season perennial grass and attains a maximum height of 3 to 6 feet. Switchgrass is currently being managed and harvested as an energy crop for biopower and biofuels. The herbicides used in switchgrass cultivation include broad-spectrum herbicides like glyphosphate, broadleaf herbicide such as 2,4-D Amine, atrazine and simazine.
  
  

Broad-Spectrum Herbicides

• Weed control is important for the successful establishment of switchgrass, particularly in the first year. If competition from weeds like crabgrass, nutsedges and Johnsongrass is not eliminated, it becomes one of the most common causes of seedling failure. One of the best ways to suppress weeds is to delay the planting of switchgrass until the emergence of the dominant grassy weeds and then spray them with a broad-spectrum herbicide like glyphosphate before the switchgrass is planted.
  
  

Broadleaf Herbicides

• Broadleaf herbicides are considered selective herbicides because they are formulated to control a specific type of weed. Broadleaf herbicides are usually not considered a major concern for newly establishing switchgrass. Although the application of glyphosphate controls broadleaf and grassy weeds before planting, some broadleaf weeds like pigweeds can emerge later and shade out the new seedlings. These can be effectively controlled with a broadleaf herbicide like 2,4-D Amine after switchgrass has reached a four-leaf stage.
  
  

Atrazine

• After the switchgrass has reached full maturity, there is often little pressure from weeds. But in some cases, weed control is required in the second year. This can be controlled with another application of glyphosphate to control the winter weeds and atrazine to control the annual grass weeds. Simazine is also an effective weed control in the young crops, and isoproturon is also often used during the dormant plant period in winter.