Scientists recommend additional herbicides for weed control in cassava farming

6 June 2020

Cassava is the second most-consumed staple food after maize in sub-Saharan Africa, feeding more than 300 million people. Nigeria is the world’s biggest producer of cassava at 59 million tons per year.

However, this food security crop that can tolerate prolonged droughts is yet to attain its yield potential. Smallholder farmers in Africa harvest 8‒12 tons of cassava per hectare against a potential of 25 tons or more per hectare. Weeds are the leading cause of this poor yield.

Manual weeding is labour intensive and cumbersome which causes farmers to delay weeding their cassava fields. Weeds account for over 30% in yeild loss
Manual weeding is labour intensive and cumbersome which causes farmers to delay weeding their cassava fields. Weeds account for over 30% in yeild loss

The most damaging effects of weeds on cassava occur during two periods: the first two-three weeks after planting when the growth rate is still low and in the third month after planting as the roots start forming. The recommended weeding schedule for cassava is at 4, 8, and 12 weeks after planting in the first growth phase. However, most farmers do not weed their fields on time, given the costly and backbreaking nature of hand-hoe weeding, on which the majority of African farmers depend. Delayed weeding leads to reduced yields since weeds compete with cassava for nutrients.  Given the difficulties of using hand-held hoes, several farmers in  Nigeria are resorting to herbicides for weed control.

The most common pre-emergence herbicides used in Nigeria by cassava farmers are formulations containing atrazine, diuron and S-metolachlor. These herbicides need to be applied at high doses if they are to be effective, which makes them quite expensive for smallholder farmers. It is, therefore, essential to provide farmers with an efficient and affordable weed management system to enhance cassava yields.

A study was carried out by researchers at the International Institute of Tropical Agriculture (IITA) to identify safe and environment-friendly pre-emergence herbicide options for weed control in cassava production in Nigeria. The results are published in a paper titled: Screening pre-emergence herbicides for weed control in cassava. The authors Friday Ekeleme, Alfred Dixon, Godwin Atser and Stephen Hauser, identified several pre-emergence herbicides (Fierce 75 WG, Merlin 75 WG, Bullet 700 SC, Gardoprim Plus Gold 500 SC, and Lagon 575 SC). These herbicides have excellent efficacy against broadleaf weeds and grasses for up to eight weeks after planting cassava when combined with good agronomic practices. “These treatments plus one post weed control at 10 weeks after planting resulted in root yields that more than doubled the national average in Nigeria.” The pre-emergence herbicide applications alone, at rates safe for cassava, did not provide adequate season-long weed control. Therefore, the researchers recommend one supplemental post weed control to supplement the herbicides.