Although many homeowners are at war with broadleaf weeds like dandelions, sometimes grasses are backyard enemy number one. Weeds in the grass family often don't respond to broadleaf weed killers such as 2,4-D, and quickly take over unattended corners of the yard. Even in maintained landscapes, particularly aggressive lawn grasses constantly invade flowerbeds. Choose the right chemical for your landscaping arsenal, and make quick work of unwanted grass.
Developed by the Monsanto company and originally marketed as the liquid weed killer Roundup, glyphosate is a nonselective herbicide. When homeowners spray it on a plant, the plant absorbs the chemical and shifts it to growing vascular tissue. This process is called translocation. It interferes with the plant's metabolism, destroying the nutrient-transporting vascular system and killing the plant in a matter of days.
Many manufacturers use glyphosate in their formulas, but the EPA has reopened research into the effects of it on the human endocrine system. For perennial grasses that are hard to kill, such as Bermuda grass, glyphosate is more effective than grass-specific herbicides, but may require repeat applications. Use glyphosate products on actively growing grasses. It does not usually affect dormant grasses.
Diquat dibromide, or simply diquat, is a contact herbicide. It is not translocated to growing areas of the grass, but instead kills only the portion it contacts. Like glyphosphate, diquat is nonselective and rapidly dessicates any plant's foliage. Use diquat to spot-treat annual grasses such as foxtail and crabgrass, but remember that it also damages turf grasses. It dries out the blades of perennial grassy weeds or turf, killing the top growth. However, roots survive and push out new blades. Diquat bonds rapidly with soil particles and is not likely to leach into groundwater or remain toxic.
MSMA (monosodium methanearsonate) is an arsenic-based grass killer. It kills grassy weeds such as crabgrass and goosegrass without harming most turfgrasses. It contains organic arsenic that, according to the University of Tennessee Extension, is less harmful than aspirin. Inorganic arsenic, on the other hand, is extremely toxic.
The EPA restricted the sale and production of MSMA after lakes in an MSMA-treated Florida golf course was found to contain high levels of inorganic arsenic. Retailers may sell existing stocks of MSMA until December 2010. Homeowners may use it until it's gone. The chemical is prohibited for use on sod farms and golf courses after 2013. It cannot be used in centipedegrass, St. Augustine grass or bahiagrass, and usually requires multiple applications for effective weed grass control.