Witchweed

Witchweed is a common name for several parasitic plants in the family Orobanchaceae, especially the genus Striga. These obligate parasites attach to the roots of host plants, extracting water and nutrients and causing severe yield losses in crops such as maize, sorghum, millet, cowpea and groundnut. The best known species are Striga hermonthica and Striga asiatica, with others including Striga gesnerioides that parasitize different hosts.

Biology: Witchweeds are parasitic plants that typically lack or have only reduced chlorophyll and rely on their hosts for most nutritional needs. They germinate when seed coats sense chemical signals—strigolactones—released by nearby host roots. After germination, the seedling forms a haustorium that penetrates the host-root tissue and withdraws water and nutrients, completing their life cycle only in association with a host.

Impact and distribution: Witchweed is most problematic in sub-Saharan Africa and parts of Asia where cereals and legumes are major crops. Infestations can reduce yields drastically, and seed banks in soil can persist for many years, allowing re-infestation after harvest and complicating control efforts.

Management: Control relies on integrated strategies, including growing crop varieties that resist infection, rotating with non-host crops, and using trap crops or cultural practices to deplete the seed bank. Sanitation to remove parasite heads, proper fertilizer management, and, in some systems, targeted herbicides or biological controls have been explored, with effectiveness varying by region and crop.