What is a Noxious Weed

 an aggressive, creeping perennial weed that infests crops, pastures, rangeland, roadsides and noncrop areas. Generally, infestations start on disturbed ground, including ditch banks, overgrazed pastures, tilled fields or abandoned sites.

Cheatgrass is an annual invasive plant that crowds out native plants in sagebrush range. Why is it bad? Wildfires, for one. Unlike perennial native grasses, cheatgrass is an annual grass that grows in the spring and then dies off between late April and June, depending on local precipitation patterns.

 Common tansy is reported to be poisonous to livestock, though it is seldom grazed due to its strong odor. It displaces forage plants, reduces wildlife habitat and species diversity. 

 Dalmatian toadflax is a perennial with extensive roots that grows up to 3 feet tall and spreads by seed and lateral roots. The overall form of the plant is narrow and upright, with multiple stems growing from a single woody base. Dalmatian toadflax causes negative impacts in pastures, rangelands, and natural areas, where it outcompetes natives or other desirable species. 

 Spotted knapweed is an aggressive, introduced weed species that rapidly invades pasture, rangeland, and fallow land and causes a serious decline in forage and crop production. Spotted knapweed has few natural enemies and is not preferred by livestock as forage. The sap of spotted knapweed can cause skin irritation in some people. 

 It is noted to invade pastures, out-compete beneficial plants and quickly spread through stressed areas. It has been noted for animal poisoning and potentially cause death. Livestock are known to become intoxicated after eating green or dried plants. 

 Houndstongue is a very strong competitor of desirable forage and is poisonous. It contains pyrrolizidine alkaloids that stop the reproduction of liver cells and is toxic to cattle, horses, goats and other livestock. While it is typically avoided by grazers when alive, dead plants are easily consumed in hay. Plants can also cause dermatitis in humans. 

 Once land becomes infested by leafy spurge, it will immediately start producing dense colonies, and use up all the water from the soil. This poses a potential threat to native plants of that region since they will have a very hard time competing with leafy spurge. With the help of its deep root system, it can extend up to 15 ft (4.5 m) under the soil as well. Leafy spurge reproduces through seed production and as many as 250 seeds can be produced by each parent plant. Once the seeds are dispersed, they can survive for up to eight years. The seeds are further dispersed by humans and water.  

 Ox-eye daisy is an aggressive invasive species. Once established, it can spread rapidly by means of roots and seeds into undisturbed meadows, woodlands, and riparian areas. It forms dense stands that tend to displace native vegetation, especially wildflowers. The end result is a species-poor plant community of use to few wildlife species.  

 Ventenata dubia is a nonnative, invasive, annual grass that has rapidly expanded in perennial grass systems, in disturbed areas and managed areas in the past two decades throughout the Pacific Northwest. Ventenata dubia is increasingly becoming a problem in managed grass-hay systems where infestations can cause yield reductions of 50% or more within a few years. 

 This plant forms dense monocultures, which displace native plant species and reduce biodiversity, wildlife habitat, and forage production. Its very extensive root system makes it very difficult to control once it has become established. All roots can develop buds that can turn into rhizomes and shoots. It is also toxic to cattle. 

 This perennial plant in the figwort family (Scrophulariaceae) occurs throughout most of temperate North America and is listed as a noxious weed in several western U.S. states and Canadian provinces. Because it contains a poisonous glucoside that may be mildly toxic to livestock, it is a particular problem in rangeland (although it is also unpalatable, so reports of livestock poisoning are rare). It is typically found in open, disturbed sites such as roadsides and waste areas or in fields, pastures, edges of forests and rangeland, where it can displace desirable grasses.