Many common weeds are not native to the areas where they are growing. Non-native plants often are not exposed to pests and diseases that they would come in contact with in their native environments. As a consequence, they tend to grow out of control. This can cause issues such as blocking water navigation, smothering native species and lowering the productivity level of farmland. Some weeds are also poisonous.
Kudzu (Pueraria lobata) is native to Japan and was imported to the warm climate of southeasten United States around 1876. It was used as livestock feed and for erosion control. Kudzu is a deciduous twining vine that grows very rapidly, adding up to 60 feet a year. It tends to inhabit disturbed areas around roadsides, fields and along waterways. The vines grow along the ground and up the trunks of trees and utility poles. Kudzu will smother all of the native plant life in a heavily infested area. It has green leaves that consist of three leaflets, each 6 inches long. The late summer flowers are pea-like and purple that later develop into flat seed pods containing hundreds of seeds. Kudzu eradication takes persistence. A heavily infested strand may take several seasons of burning, manual removal and herbicide applications to eliminate it. Because of kudzu's potential negative impact on local habitat, governments within its growing range have organized eradication guidelines on how to comply with local herbicide and burning laws and are the best sources for landowners seeking help controlling infestations.
Japanese knotweed (Polygonum cuspidatum) is another weed native to Japan that was introduced to American gardeners as an ornamental landscape plant in the mid-1800s. It since has spread to almost every state in the union. It prefers disturbed areas that are moist and will grow in full sun and full shade. It grows on canes 3 to 9 feet tall and resembles bamboo. The leaves are a rounded, triangular shape growing from the nodes on the canes. In the summer it produces large sprays of small, white-green flowers that turn to seed, which is spread by the wind. The canes die off to the ground in the winter and re-sprout in spring. Japanese knotweed spreads by underground rhizomes that reach dozens of feet from the main clump. When trying to eradicate Japanese knotweed, every single portion of root needs to be removed or it will sprout a new plant. If grown unchecked, it can smother out large tracts of native plants and clog rivers and streams.
Tansy ragwort (Senecio jacobaea) is a biennial weed that is common in pastures and disturbed areas along roadsides. It grows to 6 feet tall on a single herbaceous stem topped with a flat array of small, yellow flowers. The abundant seeds are covered with fuzzy hairs that allow them to be dispersed by the wind. Tansy ragwort is toxic to humans and animals and can cause liver damage. The toxic effects last well after the plant is dried and has the potential to contaminate hay crops. Tansy ragwort can be controlled with herbicides and by prevention. A healthy pasture will out compete tansy ragwort and removal of new plants prevents infestation. Care should be taken to remove all of the deep tap root or the plant may come back.