University of Maryland Extension

Canada thistle *

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Canada thistle *
Cirsium arvense

canada thistle in field
Flowering Canada thistle

Life cycle: invasive* perennial broadleaf weed with deep root system
Growth habit: clump-forming; grows to 2 - 5 ft. high; leaves long and narrow, alternate, irregularly lobed with spiny margins; spineless stem

 canada thistle seedling
Thistle seedling

canada thistle 
Canada thistle infestation

Reproduction: spreads by fleshy, creeping rhizomes; lavender disk flowers followed by fluffy pappus capable of floating long distances in the wind; 680 seeds produced per stem; seeds remain viable in soil from 10 - 20 years
Conditions that favor growth: infertile area without plants covering soil
Cultural control: keep vacant areas covered with turf or ground cover; maintain soil fertility appropriate for the growing crop

Additional Information 

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