Ontario Weeds: Perennial sow thistle

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Excerpt from Publication 505, Ontario Weeds, Order this publication

Table of Contents

  1. Scientific name
  2. Other Names
  3. Family
  4. General Description
  5. Habitat
  6. Seedlings
  7. Stems
  8. Leaves
  9. Flowers and Fruit
  10. Often confused with/Distinguishing features
  11. Herbicide resistance
  12. Photos
  13. References
  14. Related Links

Name:

  • Sonchus arvensis L.,

Other Names:

  • laiteron des champs, creeping sow-thistle, field sow-thistle, glandular-hairy perennial sow-thistle

Family:

  • Composite or Aster Family (Compositae)

General Description:

Perennial sow-thistle is a perennial weed reproducing by seed and by buds on underground roots.

Habitat:

Perennial sow-thistle occurs throughout Ontario in cultivated fields, pastures, meadows, woodland, waste places, roadsides, gardens and occasionally in lawns.

Seedlings

  • Leaves are broadly club-shaped
  • Leaves have irregularly toothed margins with prickles at the end

Stems:

  • Stems are erect
  • Reaching a height of 60-150 cm
  • Smooth and hairless on the lower part but glandular-hairy towards the top and on branches
  • Each hair has a tiny gland at its tip

Leaves

  • Leaves are alternate (1 per node)
  • Leaves are variable in shape
  • Lower leaves are lobed and irregularly toothed
  • Middle and upper leaves are similar but have shorter stalks and clasp the stem
  • Uppermost leaves are small and narrow, have no lobes and very few teeth

Flowers & Fruit:

  • Flower heads are bright yellow and 2.5-4 cm in diameter
  • Each flower has strap-shaped ray florets
  • Flowers from June to late autumn.

Often confused with/Distinguishing features:

The perennial sow-thistle is often confused with several weeds. The hairs with glands on its tips do not occur in smooth perennial sow-thistle which is often confused with perennial sow-thistle. It is also commonly mistaken for annual sow-thistle, spiny annual sow-thistle and dandelion.

Herbicide Resistance

No documented cases of herbicide resistance to date.

Photos:

Figure 1: Perennial sow-thistle seedling at the 2-leaf stage

Figure 1: Perennial sow-thistle seedling at the 2-leaf stage

Figure 2: Perennial sow-thistle leaf

Figure 2: Perennial sow-thistle leaf

Figure 3: Perennial sow-thistle before flowering

Figure 3: Perennial sow-thistle before flowering

Figure 4: Perennial sow-thistle flower head

Figure 4: Perennial sow-thistle flower head

References

http://www.weedinfo.ca/en/weed-index/view/id/SONAR

http://www.omafra.gov.on.ca/english/crops/facts/ontweeds/perennial_sowthistle.htm

Related Links

... on general Weed topics
... on weed identification, order OMAF and MRA Publication 505: Ontario Weeds
... on weed control, order OMAF and MRA Publication 75: Guide To Weed Control

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