Canada thistle (Cirsium arvense (L.) Scop.)
Perennial. Emerges in spring and flowers when days are the longest. Plants die after the first killing frost.
Seedlings produced from seeds emerge from soil depths of 1/4- to 1/2-inch. However, seeds have been found to germinate from 3-inch soil depths. Adventitious shoots (vegetative propagules) from creeping roots can come up from greater depths.
Mode(s) of Reproduction: Most local reproduction is from creeping roots. Seed production allows for local and long distance reproduction.
Production Range: Seed production ranges from 1,500 to 5,300 seeds per plant.
Dispersal Mechanisms: Creeping roots can be moved from field to field on tillage equipment. Each seed has an attached pappus which allows for wind dispersal.
Longevity: Low to moderate persistence - when buried 1 to 3-inches in the soil 45 to 60% of seed germinates the first year and less than 1% survives after 3 to 5 years. When buried at greater depths (7-inches or more) and left undisturbed seeds have been found to be viable for up to 30 years.
Dormancy: Though most seed is capable of germinating upon dispersal in the fall it enters secondary dormancy during the winter months.
Moderate shoot densities have been shown to reduce spring wheat yield and alfalfa seed yield by up to 50%.
Preferred Soil/Field Conditions:
Prefers perennial and no-till cropping systems and rangelands.
Predation/grazing: When present Orellia ruficauda (i.e. a seed-head fly found in Canada and the United States) can be responsible for 20 to 80% seed predation. Other agents have been studied, but eliminated for various reasons. Some livestock have been known to graze on Canada thistle at different life stages (see Chapter 5).
Decay: No information.
Tillage: Tillage, mowing and other forms of mechanical control have been deemed ineffective for control. Tillage can increase the problem by spreading vegetative propagules.
Rotary Hoeing: Not effective.
Flaming: Not effective
Crop rotation: Canada thistle populations have been shown to be reduced by the use of a summer annual cover crop such as sudangrass (See the cover crop chapter in IWM: Fine Tuning the System).
Planting date: Most likely will not affect Canada thistle infestations.
Application timing and effectiveness: Most susceptible to herbicides between the bud and flower stages of Canada thistle. Sequential herbicide applications may be necessary for control. Please refer to E-434, "MSU Weed Control Guide for Field Crops," for herbicide recommendations.