Common ragweed (Ambrosia artemisiifolia) is an annual weed throughout the northern hemisphere in cropping and rangeland
areas and causes hayfever in many individuals.
Redroot pigweed (Amaranthus retroflexus) is a coarse, erect annual
that is widely distributed around the globe in cultivated lands, gardens and waste areas.
Germination can occur at any time during the growing season when soil moisture is sufficient.
Canada thistle (Cirsium arvense) is a colony-forming perennial native of south-eastern Eurasia. It has been introduced to many new areas as a contaminant of crop seed. This aggressive weed is very difficult to control as roots are often broken up by ploughing and this seems to increase the numbers of new plants.
