How to Kill Barnyardgrass


Barnyardgrass is an aggressive annual grassy weed with the potential to reach 5 feet in height if you allow it to grow uncontrolled. In the summer months, it produces red to purple flowers. As they fade, they drop their seeds, guaranteeing a new crop of weeds to replace the current one after it dies. The first step to prevent barnyardgrass is to follow the recommended maintenance schedule for your lawn species. But if barnyardgrass is already present, you have a few other options to try.

Things You'll Need

  • Lawn mower
  • Water
  • Preemergence herbicide
  • Nonselective postemergence herbicide
  • 1- to 4-mil. clear plastic mulch
  • Rocks or bricks
  • Kill barnyardgrass seeds before they germinate by blocking sunlight, a requirement for embryo development. Mow your lawn at the highest height recommended for your grass species. Keep the blades no shorter than 2 inches to create enough shade among them.

  • Irrigate your lawn deeply and as infrequently as possible, but according to the recommended schedule for the grass species, as barnyardgrass thrives in consistently moist soil. If you have bermudagrass, for instance, give it 1 inch of water when the blades begin to wilt, allowing the soil to become somewhat dry between irrigation sessions. Barnyardgrass seeds also die before germination unless they receive regular moisture.

  • Ask your local cooperative extension office or nursery when barnyardgrass seeds usually germinate in your growing zone. Buy a preemergence herbicide labeled for use with your lawn species. Broadcast it two weeks before you expect the weed seeds to sprout. Read the manufacturer's label of the brand you selected and follow its instructions for application.

  • Spray a nonselective postemergence herbicide directly on actively growing barnyardgrass. But understand that all vegetation the chemical touches will also die. If you apply it to barnyardgrass in your lawn, you'll need to reseed the area. If you spray it in a garden bed, you might be able to protect the plants you want to keep by surrounding them with pieces of cardboard to block the herbicidal mist.

  • Kill with heat barnyardgrass growing in areas you have yet to cultivate as a lawn or garden. Mow the weeds and remove large debris from the site. Turn the soil over with a rototiller or spade and pickax. Rake the surface to a smooth bed and moisten it. Stretch a sheet of plastic mulch over the planting bed so there are no wrinkles and the material touches the ground. Use clear plastic 1 to 4 millimeters thick. Bury the edges into the soil and weigh them down with rocks or bricks. Leave the plastic mulch undisturbed for two months of summer to kill barnyardgrass. This method is known as solarization.

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