Giant Ragweed, Horseweed, Great Ragweed

(Ambrosia trifida L.)

Asteraceae (Aster Family)

▲ seedlings

▲  young plants

▲ leaves

▲ immature plant

▲ ▼ inflorescences

▲ ▼ mature plants

Giant Ragweed: (pp. 68-69, Weeds of the Great Plains; pp. 110-111, Weeds of the Northeast)

*    is a moderately-branched, large summer annual weed (3-8' tall)

*    spike inflorescence larger, longer than common ragweed, not as broad as lanceleaf ragweed; also allergenic

*    leaves are 3-5 lobed and much larger than other two annual species of ragweed (common ragweed and lanceleaf ragweed)

*    prefers moist, well-drained soils (becomes truly giant in riverbottom soils)

*    often seen along ditches and on woodland perimeters

*    also a fast-growing, aggressive competitor in agronomic, vegetable crops