Conyza canadensis

Scientific Name Conyza canadensis (L.) Cronquist
Synonyms Erigeron canadensis
Common Names English: Horseweed, Canadian Fleabane; German: Kanadisches Berufkraut; French: Vergerette du Canada; Spanish: Erígero del Canadá, hierba carnicera
Description Annual or over-wintering (facultative biennial), stinking, seed-propagated weed, often forming only one leaf rosette in the first year.

Descriptions

Characteristic Features

Leaves with toothed margins whereas the upper leaves will tend to have smooth margins, exudes a "carrot-like" odor.

Young Plant

Round-oval, rounded at the top, petiolate.

Stems

Erect, heavily foliated, ramified in the flower area, also bristly ciliate, 30-100 cm (11.81 - 39.37 inch) high.

Leaves

Undivided, linear-lanceolate, dark-green, bristly ciliate. The lower leaves tapered into the stem, the upper leaves sessile.

Propagatio Organs

Flowers

Capitulums numerous, small, in paniculiform inflorescence.
Disk florets tube-like, yellowish, several rows of ray florets, filamentous, usually dirty white.

Flowering Period

Summer - autumn.

Fruit

Achenes flattened, 2-ribbed, ivory to light brown, 1-1.2 mm (0.039 - 0.047 inch) long, appressed-puberulent. Pappus of numerous, dull white capillary bristles.

Seeds

Germination from spring-autumn.

Viability Of Seeds

2-3 years.

Propagation

Wind-dispersed seed, transportation of seeds over more than 100 km (62.13 miles).

Occurrence

Habitat

Invades shorelines and drawdown zones, roadsides, fields, waste places.

Soil

Dry, warm, sandy, loamy, and stony soils.

Agricultural Importance

C. canadiensis is slightly poisonous. It contains volatile oils, tannic acids and gallic acid that cause skin irritation in humans and livestock. The weed originates from North America and has become a troublesome weed in North America due to resistance to glyphosate.

Control

Integrated Crop Management

Tillage or a pre-plant burndown will provide season long control. A dense crop canopy prevents severe weed infestations.

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