Scouting for weeds: Perennial sowthistle
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Perennial sowthistle: Sonchus arvensis L. (view photos)
Life cycle: Erect, patch-forming perennial.
Leaves: Seedling leaves initially develop from a basal rosette
from a deep taproot. Lower leaves are alternate, blue-green, 4 to 12
inches long with two to five lobes with prickly teeth on each side,
gradually becoming smaller toward the top with a clasping base. Leaves
have a thickened midvein and exude a milky sap when damaged. Leaf
midvein is not prickly underneath.
Stems: Erect, herbaceous stem up to 5 feet tall that branches
only near the flowers. Stems are hollow and smooth with ridges and exude
a milky sap when damaged. Upper stems may have gland-tipped hairs.
Flowers and fruit: Bright yellow ray flowers are 1 to 2 inches
wide and found in clustered heads. The seed is enclosed in a
single-seeded, narrow, oval, reddish brown, ribbed, wind-disseminated
fruit.
Reproduction: Seeds and extensive creeping roots.
Similar weeds: Annual sowthistle (S. oleraceus L.) Differs by
having an annual life cycle and short taproot, less prickly leaf
margins, and pale yellow, 0.5- to 1-inch-wide flower heads. Leaf midvein
is not prickly underneath. (view photos)
Prickly lettuce (Lactuca serriola L.) Differs by having an annual or
biennial life cycle; fine prickles on leaf margins and sharp prickles on
the underside of the leaf midvein; and a many branched, spreading
panicle with numerous pale yellow flower heads less than 0.5 inch wide. (view photos)
Spiny sowthistle [S. asper (L.) Hill] Differs by having an annual life
cycle and short taproot, leaf margins with many sharp prickles, earlike
lobes where the leaf attaches to the stem, and flower heads 0.5 to 1
inch wide. Leaf midvein is not prickly underneath. (view photos)