Last Updated on October 14, 2020 by Caroline Warwick
Welcome to Weed Science Wednesday, a weekly series aimed at helping homeowners and horticulture professionals to better identify and manage common landscape weeds in Florida.
The weed of this week is ragweed parthenium (Parthenium hysterophorous). This weed is thought to have originated from the area surrounding the Gulf of Mexico and is native to Central and South America. It is mostly found in semi-arid, subtropical, tropical, and warmer temperate regions. It is found on roadsides, along railways, pastures, open woodlands, waste areas, disturbed sites, lawns, gardens, and in any area in which the soil has been disturbed. It is particularly aggressive in disturbed and degraded pastures in semi-arid environments.
Ragweed parthenium is an erect and much-branched herbaceous plant. It forms a basal rosette of leaves during its juvenile phase. The stems are erect and commonly grow 11 to 40 inches tall. The leaves are simple, alternate, whitish-green, and covered with hair on the surface. Flowers are small, borne on the stem tips, and white in color. Flowering occurs 4–8 weeks after germination and it continues until drought or frost kills the plant.
For more information on ragweed parthenium, including specific recommendations for chemical, physical, and cultural weed controls, please consult: Biology and Management of Ragweed Parthenium (Parthenium hysterophorous L.) in Ornamental Crop Production.