PURDUE UNIVERSITY
Agricultural Experiment Station
Circular No. 32
LaFayETTE, Ind., January, 1912
AGRICULTURAL EXTENSION XV
CANADA THISTLE AND ITS ERADICATION
A. G. Johnson1
Canada thistle (Carduus arvensis (L) Robs.) is one of the worst weeds to eradicate when once it becomes established. The greatest care should be taken to avoid introducing it, and every effort put forth to eradicate it where it has already found a foothold.
THE PLANT AND ITS HABITS
Canada thistle is a perennial plant, that is, it grows an indefinite number of years from the same root system. The root is of the underground, running root-stock type. At varying depths in different types of soil, and under varying conditions, these cylindrical running root-stocks, almost white in color, and one-fourth inch or more in diameter, are sent out from the main upright root. On these root-stocks, at varying intervals, buds are developed from which new upright shoots are thrown up, and above ground these develop other upright flowering shoots. When broken up by farm implements, the pieces of the root-stock have the ability of starting new plants, and where they are dragged about they start new centers of growth. The shoots that are thrown up from the root-stock early in the season, develop upright flowering shoots that same year, while those that are thrown up late in the season remain in the rosette stage until the next season, when they develop upright stalks, which bear the flowering heads. From the character of the
Resigned