Perennial sowthistle (Sonchus arvensis L.)
Perennial. Emerges in the spring, flowers throughout the summer, and sets seed in the fall. Aboveground plant tissue dies after the first frost.
Germination is reduced at depths greater than 0.25 inch, with no seeds germinating from depths greater than 1 1/4 inches.
Mode(s) of Reproduction: Reproduces by seed and the vegetative buds of roots.
Dispersal Mechanisms: Each seed has an attached pappus which allows for wind dispersal. Hooked cells on the pappus hairs can also cling to fur or clothing to help disperse seed.
Longevity: Though longevity is largely dependent on environmental conditions, seed viability has been shown to be reduced by up to 90% three years after dispersal.
Dormancy: Little to no seed dormancy.
Densities of 17 and 32 shoots per yards2 reduced wheat yield by 15 and 45%, respectively. High densities (over 83 plants per yard2) have been shown to reduce soybean and dry bean yields by 49 and 36%, respectively. In dry years these effects are exacerbated resulting in over 80% reductions in the yields of both crops.
Preferred Soil/Field Conditions:
Grows in a variety of soil types with slightly alkaline to neutral pH, preferring fine to slightly-course soils rich in nutrients.
Predation/grazing: Due to the palatability of this weed, grazing cattle and sheep help reduce populations.
Decay: No information.
Tillage: Tillage at the seven to nine leaf rosette stage reduces the reproductive capacity of root systems. Burial of plants 12-inches deep reduced new shoot emergence by 90%.
Rotary Hoeing: Not effective.
Flaming: Not effective.
Crop rotation: In South Dakota drilling crops such as soybeans, sudangrass, buckwheat, and forage sorghum after three tillage passes reduced perennial sowthistle populations by 70 to 80%. A complete year of fallow which includes spring plowing and cultivating every two to four weeks can reduce perennial sowthistle densities by 99%.
Planting date: Most likely will not affect perennial sowthistle infestations.
Application timing and effectiveness: Most susceptible to herbicides at the in the fall at the rosette stage or between the bud and flower stages of perennial sowthistle. Sequential herbicide applications may be necessary for control. Please refer to E-434, "MSU Weed Control Guide for Field Crops," for herbicide recommendations.