Horseweed

Image by: James Altland, USDA-ARS
Horseweed sometimes branches low near the soil, but rarely branches above.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Horseweed basal leaves are pubescent and lobed.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Horseweed forms a rosette in spring.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA-ARS
Flower heads are small with yellow disk flowers and tiny white ray flowers.
Image by: James Altland, USDA-ARS
Image by: James Altland, USDA_ARS
Seed heads are spherical and about 1 cm in diameter with is dirty white pappus.
Image by: James Altland, USDA_ARS
Conyza canadensis
Family: 
Asteraceae
Life cycle: 
Annual
Habit: 
Horseweed forms a small rosette in early late winter or early spring. Plants develop slowly in early spring. From the rosette, plants grow almost completely vertical. Horseweed often grows as a single vertical shoot up to 7 feet tall, with a large panicle of flowers on top. Sometimes the plant will branch low near the soil, but it rarely branches above. Leaves are dark green, hairy and without petioles.
Flowers: 
Horseweed flowers heads are small with yellow disk flowers and barely noticeable white ray flowers. Flowering occurs generally June through September, but can vary slightly. Flower heads occur in large terminal panicles. Seed heads are spherical and about 1 cm in diameter. The pappus is dirty white.
Favorable environments: 
Field
Favorable environment notes: 
Horseweed grows in areas of disturbed soil such as orchards, field nurseries, agronomic crops and unmanaged areas such as roadsides and ditches.
Dissemination: 
Seeds are dispersed mainly by wind. Very small single seeds are (1.0-1.5mm), tipped with small dirty white bristles are caught in wind currents and transported.
Management link: 
PNW Weed Management Handbook
Weed and Vegetation Management in Christmas Trees
Of interest: 
Horseweed can be confused with hairy fleabane (Conyza bonariensis), especially in the seedling stage. The seedlings of horseweed have wider leaves and are greener than fleabane’s narrower, gray-green colored leaves. In mature plants, horseweed can grow much taller than hairy fleabane. Horseweeds leaves have short stiff hairs while hairy fleabane has a combination of short, stiff and long soft hairs.
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