Scouting for weeds: Giant ragweed

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Giant ragweed (Ambrosia trifida L.)

Life cycle

Erect, branching summer annual.


Cotyledons are thick and oval to spatula-shaped and differ from those of common ragweed by being three to four times larger. Initial leaves are entire; successive leaves have three to five lobes and leaves are opposite in arrangement. Leaves are hairy and rough.


Usually hairy and rough to touch, erect and branched and up to 15 feet in height.

Flowers and fruit

Flowers are generally inconspicuous, found on terminal branches. They produce prolific amounts of pollen. The seed is enclosed in a single-seeded, woody fruit with five spikes encircling a long point, resembling a crown. Seeds are found in the axils of the upper leaves.



Editor’s note: This and more weed identification information is available in the field guide An IPM Pocket Guide for Weed Identification in Field Crops. To order, call 517-353-6740.

Young plant
Photo 1. Young giant ragweed plant.

Flowering bra
Photo 2. Giant ragweed flowering branch.

Photo 3. Giant ragweed seedling.

Photo 4. Giant ragweed leaf.

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