Chemical weed control has been researched in Africa since the 1960s but adoption has been
low or non-existent for decades. Recent evidence suggests that herbicide use in some parts of
Africa is reaching significant levels and may be on the rise more generally. Little is known
about which farmers are using herbicides in Africa and what factors drive their use. This
study aims to document trends in herbicide use and analyze the drivers of those trends in SubSaharan
Africa.
Herbicide use rates are generally increasing but vary widely by country, from 1% in Malawi
to 55% in Ghana. Kenya and Tanzania both experienced a jump in herbicide use rates from
less than 2% to about 10% in 2007 and 2009, respectively. Since then both countries have
seen minor reductions in herbicide use. In contrast, in Ghana and Zambia herbicide use is
increasing steadily. In Ghana there has been a dramatic rise from 4% in 1998 to 55% in 2013.
In Zambia there has been a moderate increase over a shorter time: from 1% in 2009 to 5% in
2013.
We used a probit model with pooled cross-sectional data from Ghana and Zambia to analyze
the factors associated with household herbicide use. The results show that increased herbicide
use is not associated with increased agricultural wage rates. Instead, in both Ghana and
Zambia households that are male headed, have more adult workers, and own more land are
more likely to use herbicides. In Ghana herbicide use is also higher among younger farmers
and in communities that are farther from extension centers, where there are tractors, and
where farming is the primary economic activity. In Zambia farmers were more likely to use
herbicides if they had received subsidized fertilizer, if the cost of commercial fertilizer was
lower, and if their previous maize price was higher. Also farmers in cotton growing areas of
Zambia, and who use minimum tillage were more likely to use herbicides.
Together these results suggest that increased use of herbicides is driven by increased
awareness, availability, and demand by better off, commercially oriented households. This
often happens in areas where agricultural productivity is rising and where the opportunity
cost of labor may be higher. This may explain why in Zambia there is a significant negative
relationship between herbicide use and agricultural wages. In Ghana there was no significant
relationship between wages and herbicide use. One way to interpret the insignificant effect of
wages on herbicide use is that agricultural wages may always be high enough to make
herbicides profitable. The use of herbicides, then, depends on their availability and farmers’
ability to invest in a labor reducing technology.
Based on this analysis, herbicide use is expected to increase in areas where agriculture
becomes more commercial. Policies to prepare for these changes should include training
farmers on safe and effective herbicide application and monitoring for contamination in water
supplies.