Monday, June 9, 2008

Weed of The Week


Thistle is the common name of a group of flowering plants characterized by leaves with sharp prickles on the margins, mostly in the plant family Asteraceae. Prickles often occur all over the plant - on surfaces such as those of the stem and flat parts of leaves. These are an adaptation to protect the plant against herbivorous animals, discouraging them from feeding on the plant.

The two most problematic Thistle species we deal with are Canada and Bull thistle. You will routinely see our staff out spraying these weeds throughout the growing season.

Canada Thistle (Cirsium arvense): is an aggressive, creeping perennial weed that infests Crops, pastures, rangeland, roadsides and non crop areas. Generally, infestations start on disturbed ground, including ditch banks, overgrazed pastures, tilled fields or abandoned sites. The Thistle crowds out and replaces native plants, changes the structure and species composition of natural plant communities and reduces plant and animal diversity. This highly invasive thistle prevents the coexistence of other plant species through shading, competition for soil resources and possibly through the release of chemical toxins poisonous to other plants.

Bull Thistle (Cirsium vulgare): It is a biennial, and sometimes annual or perennial in the sunflower family, a widespread weed that can grow in a wide range of environments but is most troublesome in recently or repeatedly disturbed areas such as pastures or home construction sites. It is found on dry and wet soils, but is most common on soils with intermediate moisture.