Witchweed

Striga asiatica, commonly known as witchweed, and other Striga species parasitize important crops such as corn, sorghum, pearl millet, sugarcane and rice.  Striga is also known to parasitize crabgrass in residential areas.   Severe attack can cause leaf wilting and chlorosis, stunted growth and death, resulting in up to 54% reduction in corn crop yields and 92% loss in sorghum. 

Native to Africa, witchweed was first found in the adjoining areas of North and South Carolina in the 1950s.  An obligate hemiparasite, witchweed must be associated with an appropriate host.  Witchweed is typically found in gardens, vacant fields, roadsides, yards and around farm buildings.  Witchweed has been found in Cumberland, Robeson, Bladen and Columbus Counties in North Carolina, and in Horry, Dillon, Marion and Marlboro Counties in South Carolina.  

Striga species have a complex life cycle that depends on finding a host plant.  Each capsule produces thousands of tiny, dust-like seeds that are dispersed after the rains at the end of the growing season.  The seeds lie dormant until host roots exude chemicals that stimulate mycorrhizal fungi colonization and signal to the parasite what type of host is present and how far away it is.  Then the mature witchweed seed germinates and develops root-like hair structures that glue the parasite to its host. The most damage occurs once the seedling penetrates the host roots, deriving all sustenance from the host.  Witchweed then emerges from the soil, develops chlorophyll, flowers, and produces seeds.

Witchweed has slender, 4-sided stems with narrow leaves emerging opposite each other.  Bright red, bilabiate flowers bloom in mid-July until a frost so it is most easily detected July through September.  Unfortunately, most of the damage caused by Striga occurs before the parasite is visible above ground.

Witchweed

DPI partners with USDA-APHIS-PPQ for the detection and eradication of witchweed in South Carolina.  If you think you have found witchweed, please contact DPI at 864.646.2140 or invasives@clemson.edu.  Please do not try to uproot the plant!

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Publications

Witchweed Poster

Witchweed ID Card

Related Links

USDA Species Profile

US Distribution Map

SC Distribution Map

Invasives.org