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Featured Pest: Common Groundsel
(Senecio vulgaris)
Common groundsel is widespread across Canada in cropland,
disturbed sites, hay land, pastures and roadsides. Generally not
a competitive weed in crops it will take advantage of distribed
or untended sites.
Biology: An annual or winter annual reproducing by seed. The
stems are erect or reclining 10 to 60 cm in height. The leaves
are alternate, fleshy, and deeply lobed and may appear
greenish-purple on the undersides. The lower leaves have
petioles and the upper leaves clasp the stem. The stems are
branched, hollow, smooth and the flower heads occur in a
cluster at the ends of branches. The seeds have a pappus of
fine white hair attached. Common groundsel is a prolific seed
producer.
Weed Act Status: Common groundsel is a noxious weed in
Manitoba. It is a non-regulated nuisance weed in British
Columbia.
Herbicide Resistance: Common groundsel is resistant to Group
5 and Group 6 herbicides in a number of countries including
resistance to atrazine (Group 5) in Ontario. Herbicide
resistance in Common groundsel is not known in Western
Canada.
Effects On Crop and Forage Quality: Common groundsel is
toxic to humans, horses, swine and cattle as it contains
pyrrolizidine alkaloids that livestock convert on ingestion into
toxic pyrroles. Sheep and goats are less susceptible. Chronic
cases result from small daily doses over a period of weeks or
months. Common groundsel is also a host for black root rot
(Thielaviopsis basicola) that affects peas, alfalfa, chickpea,
soybean and red clover.
Figure 1. Flowering Stalk
Identification: Groundsel seedlings have oblong shaped
cotyledons. Young plants can be distinguished by irregularly
lobed and toothed leaves lacking the white milky juice of many
other thistle weed species. The older plants can be identified
by their small flower heads with black-tipped involucral bracts
around the base of each flowering head.
Scouting Techniques: Since it is an annual or winter annual
weed, the emergence can extend from the fall throughout the
next season. Groundsel is very cold tolerant and will
continually flower until fall frost; hence scouting must be done
repeatedly over the season. Due to the wind borne nature of
seed spread watch for seed sources adjacent to your control
area.
Issue Date: March 18, 2015
Figure 2. Mature Plant
Similar Weeds: Common groundsel is shorter and has smaller
flowers than the sow thistle species. It has involucel bracts
which are black tipped and has fleshy lobed leaves. The
inconspicuous flowers lacking ray or strap flowers differentiate
it from the ragworts.
Tansy (Senecio jacobaea): it is a biennial or perennial but also
taller 30 to 183 cm then Common Groundsel. It has broader
and more finely divided leaves with both ray and tubular or
discoid flowers.
Tansy Ragwort (Tanacetum vulgare): is easily distinguished by
its button like yellow flowers, aromatic, fern-like leaves and
short rhizomes and it is greater height at 46 to 183 cm then
common groundsel at 10 to 60 cm.