Sow-thistle, perennial, Sonchus arvensis

Life Cycle



Reproducing by seed and from buds on widely spreading, creamy white, brittle, underground roots.


Stems erect, 60 - 150 cm high, smooth and hairless on the lower part but glandular-hairy towards the top and on branches, hollow.


Leaves of seedling plants (A) broadly club-shaped with irregularly toothed margins, the teeth ending in weak prickles (c), remnants of the cotyledons (seed leaves) (d) often visible; leaves of shoots from perennial roots (B) variable in shape, the lower ones shallowly to deeply lobed and irregularly toothed, reminiscent of Dandelion leaves but the teeth ending in small, weak prickles, with winged stalks (e); alternate (1 per node); middle and upper leaves similar but smaller with shorter stalks and clasping the stem with small, rounded basal lobes (f), or sometimes with larger basal lobes similar to those of Spiny annual sow-thistle; uppermost leaves (g) small, narrow, without lobes and with only a few teeth.

Flowers and Fruit

Upper stems, branches and involucral bracts (h) surrounding the flower heads usually densely covered with dark hair (j); each hair with a tiny gland (k) at its tip (these hairs, when seen under magnification, resemble a tiny lollipop) (these glandular hairs do not occur in its sister variety, Smooth perennial sow-thistle); flower heads showy, bright yellow, 2.5 - 4 cm across; each head containing only strap-shaped ray florets (like Dandelion flower heads and similar to those of Smooth perennial sow-thistle); seeds brown with lengthwise ridges and finer cross ridges; whole plant with sticky white juice and a rather sour odour. Flowers from June to late autumn.

Roots and Underground Structures

Widely spreading, creamy white, brittle, underground roots.


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


Corn yield loss (%)*: 4 % at 1 plant/m2 15 % at 5 plant/m2 Soybean yield loss (%)*: 5 % at 1 plant/m2 20 % at 5 plant/m2 *assumes that the weed has emerged with the crop and has been left uncontrolled all season.

Distinguishing Features

It is distinguished before flowering by its variously lobed leaves with weakly spiny teeth; its soft, somewhat fleshy, bright green stems mostly arising directly from horizontal yellowish-white, fleshy, brittle, cord-like roots (b), these roots bearing many, small, whitish buds (a) able to grow into other new leafy stems; and the whitish vertical underground portion (m) of each upright stem resembling a root, but usually not tapering downwards except in first-year plants (A) which started from seed. Flowering plants are distinguished by their showy, large, bright yellow flower heads and the covering of glandular hairs (j) on the involucre (h) and the upper stems and branches.


Perennial sow-thistle is not know to be toxic.

Human Health Issues

Perennial sow-thistle is not a known allergen.

Forage Quality

No information exists at this time.

Species Benefits

"The young leaves can be added to salads or boiled for 10-15 minutes and eaten." From: Peterson, LA, 1977, A Field Guide to Edible Wild Plants of Eastern and Central North America, Houghton Mifflin Company, New York.

Often Mistaken For

Dandelion (TAROF), Annual sow-thistle (SONOL), Smooth perennial sow-thistle (SONAU), Spiny annual sow-thistle (SONAS).

Power Ranking Corn

Power Ranking

↑ 16


Power Ranking Soybeans

Power Ranking

↑ 8


Biological Control

BIOCONTROL AGENT Tephritis dilacerata (Diptera: Tephritidae) WHAT DOES IT DO? Transforms flower buds into a button shaped galls. Larval feeding of T. dilacerata causes the base of the bracts to enlarge so they cannot open. This modification gives the larvae time to complete development, but the gall is not a metabolic sink. The larvae normally consume the entire receptacle and floret primordia, so attacked heads produce no seed. The fly, which overwinters as an adult, occurs through central and northern Europe. From 1979 to 1994, around 6,000 flies were released in Alberta, and 2,000 each in Saskatchewan, Quebec, Nova Scotia and Prince Edward Island, but have not been recovered. AVAILABILITY: To find out about availability of this biocontrol agent ------------------------------------------------- BIOCONTROL AGENT Liriomyza sonchi (Diptera: Agromyzidae) WHAT DOES IT DO? Larvae mine the leaves.Liriomyza sonchi is a leaf mining fly. The females deposit an average of 140 eggs singly through the upper epidermis of the leaf. Larvae form blotch mines and sometimes several larvae occur in a mine (Peschken and Derby 1988). Most larvae pupate in the debris of the soil surface. In Europe there are two generations (Hendel 1931-1936). Females suck plant sap from wounds produced with their ovipositor. From 1987 to 1991 over 9,000 pupae and adults were released between Nova Scotia, New Brunswick and Saskatchewan, but have not been recovered. AVAILABILITY: To find out about availability of this biocontrol agent ------------------------------------------------- BIOCONTROL AGENT Cystiphora sonchi (Diptera: Cecidomyiidae) WHAT DOES IT DO? Creates pustule galls on the leaves. AVAILABILITY: To find out about availability of this biocontrol agent -------------------------------------------------

Biopesticide Control

Currently none available for this weed in corn and soybean.

Herbicide Resistance

No documented cases of herbicide resistance to date. For more information on weed resistance:


Noxious under the Ontario Weed Control Act.

Figure #1.

Perennial sow-thistle. A. Young plant from seed. B. Base of plant from perennial root. C. Top of flowering stem.

Figure #2.

A 2-leaf seedling plant.

Figure #3.

Photo taken in Spring, Southwestern Ontario.

Figure #4.

Perennial sow-thistle leaf.

Figure #5.

Perennial sow-thistle prior to flowering.

Figure #6.

Perennial sow-thistle flower head.