Striga, commonly known as witchweed,[1] is a genus of parasitic plants that occur naturally in parts of Africa, Asia, and Australia.

Witchweed parasitizes maize, millet, sorghum, sugarcane, rice, legumes, and a range of weedy grasses.

[5] Host plant symptoms, such as stunting, wilting, and chlorosis, are similar to those seen from severe drought damage, nutrient deficiency, and vascular disease.

[16] Finger-like structures on the haustorium, called oscula (from Latin osculum, "little mouth") penetrate the host xylem through pits in the membrane.

[5] Seeds have been shown to survive in frozen soil of temperatures as low as −15 °C (5 °F), attesting to their aptitude as overwintering structures.

[5] These findings, while limited to the Carolinas in the United States, seem to suggest that the pathogen could successfully infect the massive corn crops of the American Midwest.

Striga in the United States has been controlled through the use of several management strategies, including quarantines imposed on affected areas, control of movement of farm equipment between infected and uninfected areas, herbicide application, and imposed "suicidal germination".

For the latter, in fields not yet planted in crops, seeds present in the soil are induced to germinate by injecting Ethylene gas, which mimics the natural physiological response tied to host recognition.

Unfortunately, each mature Striga plant can produce tens of thousands of tiny seeds, which may remain dormant in the soil for many years.

Another method called trap cropping involves planting a species in an infested field that will induce the Striga seeds to germinate but will not support attachment of the parasite.

[23][24] Increasing nitrogen levels in the soil, growing Striga-tolerant varieties, trap-cropping, and planting susceptible crops harvested before witchweed seed is produced, are proven tactics.

Because of Striga, the Animal and Plant Health Inspection Service (APHIS) of the U.S. Department of Agriculture established a research station and control methods.

[13] Through infestation mapping, quarantine, and control activities such as contaminated seed destruction, the acreage parasitized by witchweed has been reduced by 99% since its discovery in the United States.

[13] APHIS has even offered cash rewards those who identify and report the weed, and encourages landowners to check their own acreage.

[31] The majority of crops in Africa are grown by subsistence farmers who cannot afford expensive witchweed controls, who therefore suffer much as a result of this pathogen.