The weeds on this page were originally published on the Whitman County Weed of the Month/Invasive Weeds of Crop and Non-crop Weed Index website. They are republished here by permission of Stephen Van Vleet, WSU Whitman County Extension.
Catchweed bedstraw, Galium aparine L., native to North America and Eurasia, is an annual broadleaf plant with a shallow, branching taproot. The stems of catchweed bedstraw are square in cross-section, weak, mostly unbranched, and grow to about 6 feet long. Catchweed bedstraw prefers shady, moist sites, but tolerates full sun with sufficient moisture. Commonly found in waste sites, roadsides, and other disturbed areas, catchweed bedstraw can grow in a variety of habitats, including along fence lines and in forests and woodlands, meadows, prairies, abandoned fields and cultivated crops.
Downy brome, Bromus tectorum L., was introduced into North America from the Mediterranean area of Europe and is a winter annual that usually begins growing in the fall or early spring. It thrives in all soils. This weed has an extensive shallow root system and roots with many hairs which enable the plant to extract much of the soil water.
Field Bindweed, Convolvulus arvensis L., was introduced from Eurasia. It is a long-lived perennial with an extensive root system, reaching depths of 20 to 30 feet and repeatedly giving rise to numerous long rhizomes (horizontal roots). Field bindweed reproduces by seeds and regenerates new plants from adventitious buds on roots and rhizomes. It is spread by animals, drainage water and machinery, as well as a contaminant of crop seed.
Horsetail, Equisetum arvense L., belongs to a prehistoric plant family that was dominant in the world 230 million years ago and significantly contributed to the formation of coal deposits. The Equisetum family contains over 30 plant species and is native nearly worldwide, excepting Australia, New Zealand, and Antarctica. The Pacific Northwest is home to about 20 Equisetum species.
Horseweed, Conyza Canadensis L. Cronq., is a winter or summer annual, native to North America. The plant grows upright, tall and narrow, and is unbranched at the base unless damaged. A dense inflorescence is borne at the end of branched stems, with small white ray and yellowish disk florets. The leaves and flowers contain a terpene, which may cause skin and mucosal irritation in humans and animals and may inhibit grazing.
Italian ryegrass, Lolium multiflorum Lam., is native to southern Europe, Italian ryegrass is a cool-season, annual or biennial bunchgrass. Mature plants grow 1 to 3 feet tall. Stems (culms) are often purplish at the base, and consist of nodes and internodes. Italian ryegrass regenerates entirely by seed, and germinates readily with sufficient moisture. The plant is best adapted to cool, moist climates, and grows best between 68 and 77°F.
Jointed goatgrass, Aegilops cylindrica, is a winter annual grass native of southern Europe and western Asia. Jointed goatgrass is generally found in areas of 10 to 20 inches of annual rainfall and in elevations of 800 to 4,000 feet.
Kochia, Kochia scoparia L., native to Eurasia, is an annual plant that reproduces from seeds. It has a deep taproot and network of fibrous roots. Mature plants typically range from one to four feet tall, but can grow several feet taller. Because most kochia seeds do not live more than a year, preventing seed production for a single year will significantly reduce the following year’s infestation.
Also known as Dog Fennel, Stinkweed Description Mayweed Chamomile, Anthemis cotula L., is native to the Mediterranean region, but has been widely introduced as a weed in the temperate zones. In 1995, it could be found in almost all of the lower 48 states. Mayweed is an annual bushy, ill-scented herb.
Prickly Lettuce, Lactuca Serriola L., a native to the Mediterranean region is also called wild lettuce, China lettuce or compass plant. The plant is sometimes called the compass plant, because the leaves on the main stem are held vertically in a north-south plane, perpendicular to direct sunlight. Prickly lettuce may be mistaken for dandelion, at the rosette stage, or for sow-thistles at any stage. All of these species are members of the sunflower family, contain milky latex, and produce numerous wind-dispersed seeds.
Rattail fescue (Vulpia myuros) is believed to have originated from Eurasia. Rattail fescue establishes readily and is highly invasive in Mediterranean ecosystems, however, this weed is also widespread throughout temperate and subtropical regions. The greatest populations of rattail fescue exist in the western United States, especially throughout Arizona, California, Idaho, Nevada, Oregon and Washington.
Rush Skeletonweed, Chondrilla juncea L., originated from Eurasia and belongs to the sunflower family. Once established, rush skeletonweed can reduce crop yields by as much as 70 percent. The high fibre content and milky juice in the stems also greatly hamper harvest and tillage operations. Rush skeletonweed infiltrates roadsides, waste areas, disturbed soil, wheat and farm land.
Russian-thistle, Salsola tragus L., Salsola iberica Sennen, introduced from Russia, is a summer annual in the goosefoot family that reproduces by seed. Russian thistle plants break off at the base after maturity and tumble with the wind, scattering seeds over great distances. A single plant can produce 250,000 seeds, which typically remain viable for a year. Russian thistle is commonly found in dryland fields, along roadsides and in disturbed areas. It can reduce yield and quality of crops.
Ventenata (Ventenata dubia (Leers) Durieu) is native to central and southern Europe, Asia, and Africa. Ventenata has established itself in a number of states in the United States and provinces in Canada. It is currently increasing its expansion across the Pacific Northwest and will continue to spread, particularly as a contaminant in grass seed.