MSc. Dissertation 2018Cassava (Manihot esculenta Crantz) is one of the important crops in the world for food and income security. Cassava production is challenged by weeds as they reduce yield to 100%. Effective weed management in cassava production depend determination of weed species diversity and determination of Critical Period for Weed Removal (CPWR). A study was conducted in Zambia, to document weed species diversity in cassava growing areas of Chongwe and Kaoma districts in Zambia, determine the critical period for weed removal in three cassava varieties (Nalumino, Mweru and Chila) commonly grown and estimate yield losses caused by weeds on cassava farms in the two districts. Farmer survey was done to get farmers experience in weed management. The experiment was established whereby, two weeding regimes were applied; weed free (WF) and weed infested (WI). Sampling of weeds for density, species diversity and yield components was done within the period of 21 days until 168 Days After Planting (DAP). Weed species diversity index in Kaoma was 2.12 and Chongwe was 3.487 (Shannon diversity index) Forty weed species in Chongwe and 33 in Kaoma were identified. Findings reveal that CPWR was between 42 and 105DAP. Cassava root yield 6 months after planting in weed free plots was significantly higher than in weed infested treatments. All varieties were affected by weeds, and under un controlled weed condition the loss of 99.9% was recorded. Therefore, keeping the crop weed free during the first four months of growth is important for all varieties in order to reduce significant yield penalty. Additionally, further studies on weed seed bank and herbicide screening is important to postulate appropriate weed management and reduce drudgery respectively.