An invasive weed with close relatives among native species is a challenge for biological control. Houndstongue was introduced accidentally to North America from Eurasia in the mid-19th century. It has since invaded most Canadian provinces and adjacent US states. There are many native plants in the USA in the same family as houndstongue. CABI staff in Switzerland are investigating specialized natural enemies in the area of origin of the weed that could be introduced as biological control agents.
Trade in seed brought crops to new regions, but many weeds were spread by this route too. Whitetops, also known as hoary cresses, arrived in the USA as contaminants of seed from Eurasia. They are now aggressive invaders of crops, rangeland and riverbanks. One reason for this is the absence of the natural enemies that keep them in check in their area of origin. CABI staff in Switzerland are looking into the prospects for biological control of these invasive plants.
Dyer’s woad is an ancient source of blue dye and was grown as a textile dye crop in Europe and Asia for centuries. It was introduced to North America by early colonists, but escaped cultivation. Today, it is recognized as a serious weed in the western USA. One reason for its impact is the absence of the natural enemies that keep it in check in its area of origin. CABI is searching for specialist natural enemies in Europe that could potentially be introduced for its biological control.
Despite the name, Canada thistle’s natural home is Eurasia. It has spread throughout the temperate world to become one of the worst weeds in rangeland and crops. One reason for this is the absence of the natural enemies that attack it in its area of origin. In North America six insect natural enemies have been introduced as biological control agents to try to control the weed but they have had little impact. CABI has been investigating whether disease-causing fungi might be the answer.
Swallow-worts (Vincetoxicum nigrum and V. rossicum) are Eurasian plants that have become invasive in North America. The overall goal of the project is to identify specific natural enemies that can be introduced to North America as biological control agents for swallow-worts.
Native to Europe, toadflaxes were introduced to the USA and Canada over 100 years ago as ornamental plants. They now occur over much of temperate North America and are declared noxious in eight US states. CABI identifies specific natural enemies that can be introduced into North America as biological control agents to reduce the vigour, density and spread of this invasive plant.