Prevention is the key to controlling lawn weeds. Once established, weeds can quickly dominate, set seeds, and spread their colony. Many weeds, imported from all over the world, have found the Southwest’s climate very inviting. Invasive weeds have many disagreeable attributes–many disperse clouds of irritating pollen, others have incredibly deep roots, spreading rhizomes, or prickly spines and thorns.
A number of spurges are invasive weeds in the Southwest. Spurges are related to poinsettias, but are much less desirable. All spurges can be identified by white latex sap in the stems. Leafy spurge is characterized by its narrow needle-like leaves. This spurge can grow up to three feet tall with spreading roots that extend 25 feet below the surface. Spotted spurge is another common lawn weed. This leafy plant grows along the ground, colonizing bare spots in turf grass. Spotted spurge is easily recognized by the reddish purple spots on the predominately green leaves. Spotted spurge is a shallow-rooted plant that can be pulled or hoed when young. To remove leafy spurge or mature spotted spurge use a broad spectrum weed killer like glyphosate (RoundUp or KleenUp.) Re-seed bald patches with a perennial ryegrass after applying weed killer.
Dandelions are the most-common and most-easily recognized lawn weed across the US and in the Southwest. Unfortunately, they are one of the hardest to remove. Dandelions have notoriously long taproots. In the spring they will grow back after a weed killer application. Instead use weed killer in the fall when dandelions are less vigorous, or use a mechanical device like the Weed Hound or Weed Popper, which spear the root and pull it out of the ground.
Scotch Thistle and Musk Thistle are two of the most pesky turf weeds across the Southwest. Both have purple flowers, large spiny leaves, up to two feet long, which grow around a central taproot. Thistles invade turf grass, fence and property lines indiscriminately. Cut flower buds to prevent seed dispersal. Thistles require the most powerful weed killers on the market. Look for weed killers with 2,4-D and at least one other active herbicide ingredient. Tordon and Curtail are approved for managing these thistles. For smaller populations use boiling water to kill the leaves, then sever the taproot with a trowel or shovel.
When applying weed killer read all directions carefully and follow safety recommendations.
New Mexico State University, The University of Arizona, & Utah State University, and U.S. Department of Agriculture, “Leafy Spurge” Invasive Weeds of the Southwest.
PBI/Gordon Corporation ,”Spotted Spurge” WeedAlert.com.
Sunset Publishing Corp. and Gale Group, “Time to Battle Spotted Spurge” BNET.
Dawn West, “Weed Control Tips to Defeat Dandelions” All About Lawns.
Northwest Coalition for Alternatives to Pesticides, “Dealing with Dandelions” NCAP Northwest Coalition for Alternatives to Pesticides.
New Mexico State University, The University of Arizona, & Utah State University, and U.S. Department of Agriculture, “Scotch Thistle” Invasive Weeds of the Southwest.
New Mexico State University, The University of Arizona, & Utah State University, and U.S. Department of Agriculture, “Musk Thistle” Invasive Weeds of the Southwest.
New Mexico State University, The University of Arizona, & Utah State University, and U.S. Department of Agriculture, “Musk Thistle Management” Invasive Weeds of the Southwest.