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Giant Ragweed, Horseweed, Great Ragweed

(Ambrosia trifida L.)

Asteraceae (Aster Family)

▲▼ seedlings

▲  young plants

▲▼ leaves

▲▼ leaves

▲▼ immature plants

▲ stem, showing hairs, ridges

▲ ▼mature, flowering plants

▲▼ mature, flowering plants

 

▲▼ mature, flowering plants

 

▲▼ inflorescences

▲▼ inflorescences

▲▼ male inflorescences (above) at top of spike; female inflorescences (below) at bottom

 

Ambrosia trifida L., Giant Ragweed: (Bayer Code:  AMBTR; US Code AMTR)

         Is a moderately-branched, large summer annual weed (normally 3-8 feet tall, but can grow up to 15 feet tall or more)

         Spike inflorescence larger, longer than common ragweed; also allergenic

         Leaves are 3-5 lobed and much larger than common ragweed or lanceleaf ragweed

         Prefers moist, well-drained soils (becomes truly giant in river bottom soils)

         Often seen along ditches and on woodland perimeters

         Is a fast-growing, aggressive competitor in agronomic, vegetable crops

 

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Updated 19 January 2019