POPULATION-MODEL OF THE PARASITIC WEED STRIGA-HERMONTHICA (SCROPHULARIACEAE) TO INVESTIGATE THE POTENTIAL OF SMICRONYX-UMBRINUS (COLEOPTERA, CURCULIONIDAE) FOR BIOLOGICAL-CONTROL IN MALI

A simulation model of the population dynamics of Striga hermonthica (Del.) Benth. was developed for a millet cropping system in Mali. The potential of Smicronyx umbrinus Hustache as a biocontrol agent of S. hermonthica was investigated. The method showed that Sm. umbrinus, used as the sole control agent, would have to destroy approximately 95% of S. hermonthica seeds each year to reduce the emerged plant density by 50%. Such a high rate of seed destruction would be necessary because the S. hermonthica seed bank does not limit the parasite density in most situations. Crop rotation of 1 year of millet followed by 3 years of fallow or another crop reduces the emerged equilibrium density of S. hermonthica to 61% of that with no control, and destruction of an additional 22% of seeds by Sm. umbrinus would decrease this to 50%. Sm. umbrinus in conjunction with weeding docs not become effective until the seed bank is limiting at very high levels of weeding.