Sub-Saharan Africa (SSA) has the world's largest human population growth rate, some of its poorest soils, and a high incidence of crop pests. Weeds are the major pest in virtually all of the agro-ecological zones of SSA. Parasitic and perennial weeds dominate the savanna vegetation zones whereas rapidly growing annual weeds overwhelm crops in the forest vegetation zones. High weed pressure coupled with inefficient weed control practices have tied up a disproportionate percentage of SSA's economically active population in the primary task of food production and also have kept crop yields down. In the absence of organized weed research and professional training in weed science to meet the needs of the region, improved cultivars of virtually all crops fall prey to weeds, and available arable land becomes limited to that area that can be kept free of weeds. A preponderance of annual weeds in humid parts of SSA together with hard-to-kill perennial grasses and parasitic weeds in the subhumid and arid agro-ecological zones hamper crop production and frustrate farmers throughout the region. Sustainable food production in the region can be achieved by introducing improved weed management technologies and by addressing other food production constraints of the region.

Introduction. Small-scale bananaproducers in Tanzania are facing constraints caused by the destructiveactivities of the banana weevil (Cosmopolites sordidus Germar).Many currently used methods of addressing the problem are ineffective ortoo expensive for local farmers to implement. Materials and methods.A combination of two integrated pest management (IPM) tools (regulartrapping in combination with field sanitation) was tested at twofarmer-managed sites (Bujela and Kyimo) and one researcher-managedsite (SUA-Morogoro). Treated areas were surrounded by untreatedcontrol areas where no trapping and limited sanitation was done.Changes in population densities were estimated by the mark-recaptureprocedure and the Lincoln index. Results and discussion. Aftereight months, weevil populations in the cleaned and trapped areashad been reduced by 33% (Bujela), 33% (Kyimo) and 74% (SUA). Thechange in population sizes in the control areas differed greatly,possibly due to discrepancies in field management between farmers’ andresearchers’ practice. Trap types, areas and sites affected thenumber of weevils captured. Disc-on-stump (DOS) traps captured moreweevils than corm disc (CD) and pseudostem (PS) traps. Weevils respondedmore strongly to traps in the clean area at SUA compared with theother two sites, probably because the more rigid sanitation practicesat SUA meant that volatiles from the traps were less likely to bemasked by volatiles from surrounding residues. Conclusion.Regular trapping with field sanitation can greatly reduce populationsof banana weevils, but strict adherence to method execution is requiredin order to gain favourable results.

In 14 forest plots (36 m2) all terrestrial plant species were recorded before slashing and burning of the vegetation. During subsequent cultivation with rainfed rice all resprouting plants were registered in permanent plots (72 m2). The fields studied (one per forest) covered all combinations of forest type and soil usually cultivated on local farms. Forest plots (total 409 species) and field plots (358 species) had 226 species in common. Most resprouting plants were woody. Though nine forests in the sample were secondary, 70% of resprouting plants belonged to primary forest species and with three exceptions, these species did not regenerate by seed.

Experiments in one field inlcuded: different intensities of initial burning, weeding (none, once, twice) and length of the rice cultivation period (1, 2, 3 y). Resprouting plants were monitored in permanent plots (108 m2) during 3 y of cultivation and 2 y of fallow. More plants resprouted after a mild initial burning (5.8 plants m−2) than after a burn of normal intensity (1.4 plants m−2). Weeding and prolonged cultivation strongly reduced species diversity but plant densities were less affected because some climbers and trees were apparently stimulated and expanded.

Fields abandoned after one rice harvest had, within six months, a closed forest canopy of pioneer trees emerging from the pre-existing seed bank and from the growth of resprouting trees. Prolonged cultivation (3 y) destroyed the pre-existing seed bank but affected sprouting plants less, these being the only component in the vegetation able to shade out weeds and forbs such as Chromolaena odorata.

A millet farm was divided into five treatment plots of three replicates. The population of the grasshoppers was assessed by flushing and the percentage leaf damage on the millet was estimated by visual grading of the defoliated area. Weeding discouraged oviposition and reduced the vegetative shelter and the population of the grasshoppers. The unweeded plots had high levels of defoliation and low grain yield of millet relative to the weeded plots. Oedaleus spp were the most numerous grasshoppers and probably caused the greatest damage on pearl millet. The common weeds on the farm were Brachiaria xantholeuca, Cenchrus biflorus, Ipomoea vagans and Mitracarpus scaber.