• What is a Weed Management Area
• Why is it important to control invasive weeds
• Who belongs to the Los Angeles County WMA
• Weed Management Area Activities
• Major Invasive Weeds in Los Angeles County
• Other weeds of concern
• What can you do to help?
• Download the LA County WMA Information Pamphlet
• Children's book on invasive weeds
• Download:"Best Management Practices for Vegetation Management" (PDF/6.5 MB/56 Pages)
• Links

There are many species of invasive weeds known to exist in Los Angeles County. Of these only three (that we know about) are considered highly invasive and are listed as "A" rated by the California Department of Food and Agriculture (CDFA). All three are targets of eradication efforts aimed at completely eliminating them from the County. Sightings should be reported to the County Agricultural Commissioner's Office. They are:

Alligatorweed (Alternanthera philoxeroides)

Alligatorweed is an aquatic weed that grows in shallow water and forms dense interwoven floating mats that extend over the surface of deeper water. Mats become dense enough to support the weight of a person. Floating mats can break away and spread the infestation to new sites. These dense mats can disrupt the ecology of the body of water they infest by reducing light penetration and crowding out native species. Serious infestations can create anoxic, disease, and mosquito breeding conditions. Alligatorweed was first discovered in LA county in the 1960's behind the Whittier Narrows Dam. Extensive surveys were conducted over several years, including door to door, when it was found infesting residential neighborhoods, and over 200 acres were eventually identified as infested. Today, after thirty years of hard work and millions of dollars, the area of known infestation is less than 1/4 of an acre.

Halogeton (Halogeton glomeratus)

Halogeton invades disturbed arid and semi-arid sites with alkaline to saline soils. Plant tissues accumulate salts from deeper in the soil and become concentrated in the plant. These salts leach out of dead plant material, increasing topsoil salinity and favoring halogeton seed germination. Some salt in the foliage contains soluble oxalates toxic to livestock, especially sheep. Animals in poor condition are at greater risk of poisoning than well-nourished ones. As little as 12 ounces of foliage can be fatal to animals in poor condition. The current Halogeton infestation is found near Highway 14 in the Antelope Valley.

Spotted Knapweed (Centaurea maculosa)

Spotted Knapweed is a non-native thistle introduced from Europe, probably as a contaminant of animal feed. It is an aggressive biennial or short lived perennial that forms dense infestations in disturbed sites that eventually move into undisturbed areas. Spotted Knapweed reduces biodiversity by out competing native vegetation, may cause soil erosion, reduce forage for wildlife and livestock, and reduce appraised land values. Spotted Knapweed currently infests the Tanbark Flats area of the San Dimas Experimental Forest and a small area near a hiking/equestrian trail in Charmlee Park in Malibu. Recently, a single plant was detected in Lancaster near the Kern County border. Spotted Knapweed is considered to be one of the most serious weeds in the Western U.S.