Abstract

Cassava (Manihot esculenta Crantz) is an important crop for food, feed and income security. Cassava productivity is limited by poor weed management. Field trials were conducted in Zambia to determine the Critical Period for Weed Removal (CPWR) on 3 cassava varieties (Chila, Mweru and Nalumino), with contrasting canopy structure, using a split-plot design in randomized blocks. Nine weeding treatments, i.e., control, 21, 42, 63, 84, 105, 126, 147, 168 days after planting (DAP), were applied on two sets of weeding regimes. In one set, weeds were allowed to grow followed by a weed free period while in the second, plots were kept weed-free followed by a period of natural weed infestation at Kabangwe and Kaoma. Cassava varietal means were in the order Chila (10,199 kg ha^-1) > Nalumino (9,047.6 kg ha^-1) > Mweru (8,429 kg ha^-1). Chila, a branching cassava variety, significantly out-yielded (P < 0.05) other varieties. Fresh cassava root yields were higher at Kabangwe (23,270 kg ha^-1) compared to Kaoma (21,347 kg ha^-1). The CPWR was determined to be 60 DAP (48-73 DAP), at both sites. Yield differences among weeding treatment ranged between 18% and 75%. The determined CPWR is a determinant of weed management strategy for branching cassava varieties. The branching canopy architecture smothered weeds and hence is considered an important cassava varietal attribute. The yields in the current study are doubled the regional yield average of 8000 kg ha^-1 and four times the Zambian average of 5000 kg ha^-1.

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