Worldwide, the majority of the plant species that are developing herbicide resistance are those that occur as weeds in agricultural environments, on roadsides and in other rights-of-way. In contrast, herbicide resistance is not nearly so common in weeds of natural areas or rangelands. A search of the International Survey of Herbicide Resistant Weeds ( weedscience.com ) revealed no herbicide-resistant weeds (i.e., invasive nonnative species) listed for terrestrial natural areas anywhere in the world, and only two resistant weeds listed for aquatic areas, both of them in Florida. In pastures, 15 species worldwide have developed resistance, eight of which are considered primarily as agricultural weeds. Only two of those 15 are found in pastures within the United States, and none occurs in any Western state.

Stinkwort (Dittrichia graveolens) is a Mediterranean native that has become a weed in areas of Europe as well as in Australia. This strongly aromatic weed was first reported in California in 1984 in Santa Clara County, and it had spread to 36 of the 58 California counties by 2012. Stinkwort is not palatable to animals, and can be poisonous to livestock and cause contact allergic dermatitis in humans. In California, this weed is found primarily along roadsides. However, the biology of this annual plant suggests that it could also invade open riparian areas and overgrazed rangelands. Stinkwort has an unusual life cycle among annual plants: Unlike most summer or late-season winter annuals, stinkwort flowers and produces seeds from September to December. Such basic biological information is critical to developing timely and effective control strategies for this rapidly expanding weed.

Native plants of California's chaparral are adapted to natural wildfire, re-establishing within a few years after a fire. Non-native plants can upset this balance and allow wildfires to recur too soon. Learn to recognize and control these problem plants.

An herbicide ceases to be a useful tool for farmers when its target weeds develop resistance to its effects. This publication helps you understand resistance: what causes it, and how you can slow or prevent its development.

Small smutgrass is a grass that grows well in irrigated pastures but is not palatable to livestock. So what happens if it grows well and it doesn't get eaten? It takes over the pasture! Learn some simple control measures that will keep this weed in check

Preventing plant invasions or eradicating incipient populations is much less costly than confronting large well-established populations of invasive plants. We developed a preliminary determination of plants that pose the greatest risk of becoming invasive in California, primarily through the horticultural industry. We identified 774 species that are invasive elsewhere in Mediterranean climates but not yet invasive in California. From this list, we determined which species are sold through the horticulture industry, whether they are sold in California and whether they have been reported as naturalized in California. We narrowed the list to 186 species with the greatest potential for introduction and/or invasiveness to California through the horticultural trade. This study provides a basis for determining species to evaluate further through a more detailed risk assessment that may subsequently prevent importation via the horticultural pathway. Our results can also help land managers know which species to watch for in wildlands.

Barb goatgrass is a winter annual grass native to Europe and western Asia. It first appeared in California in the early 1900s, but only recently has it begun to spread widely, crowding out native vegetation. Learn to identify and manage this hardy weed.

The expected production of biomass-derived liquid fuels in the United States may require cultivation of millions of acres of bioenergy crops, including perennial grasses such as switchgrass. Switchgrass is not native to California and possesses many qualities in common with other perennial grasses that are invasive. To evaluate the potential invasiveness of switchgrass in California, we conducted risk analysis and climate-matching models as well as greenhouse and field evaluations of switchgrass, looking at its environmental tolerance and competitive ability against resident riparian vegetation. We concluded that dryland regions of California are not suitable to vigorous establishment and invasion of switchgrass. However, riparian areas appear to be far more likely to support switchgrass populations. With effective mitigation practices in place throughout the development, growth, harvest, transport and storage processes, it should be possible to minimize or eliminate the movement of seeds and vegetative propagules to sensitive habitats. Consequently, we believe that switchgrass is unlikely to become a significant problem in California, even with widescale production.

Horses, goats, sheep, and cattle can sicken or die if they eat from a poisonous plant. The best strategy is just to keep these plants out of reach. Here are photos, ID info, and poisoning symptoms for more than 30 hazardous ornamental and range plants.