Witchweed, a destructive parasitic plant that preys on crop plants of the grass family, such as corn, sorghum, and sugarcane. It was originally confined to Asia and southern Africa but now grows in the United States as well.
Witchweed is hard to eradicate because one plant can produce up to 500,000 tiny seeds, which may lie in the ground up to 20 years before sprouting. A seed germinates only when stimulated by chemicals secreted by a host root growing near it. Then the parasite penetrates the host root and sucks out water and food.
After growing underground for several weeks as a complete parasite, witch weed sends green shoots, which bear fuzzy leaves and reddish flowers, above ground. Once leaves develop, witchweed begins to make its own food. But it still takes water and minerals from the host plant, and eventually kills it.
Among methods used to fight witchweed are the spraying of chemical pesticides and the planting of catch crops. Catch crops consist of plants, such as corn, that witchweed normally feeds on. Before the witchweed goes to seed both the crop plants and the witchweed are destroyed.
Witchweed is Striga asiatica of the figwort family, Scrophulariaceae.