Kendall County (IL) Forest Preserve District
Giant Ragweed
(Great Ragweed)
Ambrosia trifida [C-value
0]
Aster family (Asteraceae)
Blooms August -
September
The native Giant Ragweed is very common in our area and is on the Illinois Noxious Weeds List. This nasty weed can be found in almost any sunny area including vacant lots, cropland, poorly drained waste areas and roadsides. In full sun and moist fertile loamy soil, this annual can develop into a huge plant up to 12' tall, branching occasionally, with green stems covered with white hairs. The opposite leaves are up to 12" long and 8" across. The larger leaves are divided into 3 or 5 lobes on long petioles. Upper stems terminate in a cylindrical spike (3-6" long) of flowers that are are yellowish green occurring in small drooping clusters less than ¼" across. The fine pollen of the male flowers is easily carried aloft by the wind causing problems for many Ragweed allergy sufferers.
Giant Ragweed in bloom along Minkler Road August 22, 2013
Giant Ragweed at Pickerill/Pigott Forest Preserve August 11, 2012
Giant Ragweed bloom spike at Baker Woods Forest Preserve August 19, 2013
Giant Ragweed pre-blooming at Baker Woods Forest Preserve August 19, 2013
Giant Ragweed foliage at Baker Woods Forest Preserve August 19, 2013
Giant Ragweed seed heads at Richard Young Forest Preserve October 14, 2015
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