Involving grain traders in determining the effect of post-harvest insect damage on the price of maize in African markets

Quantifying the loss in value of maize associated with insect damage can be difficult where commodities are sold using non-standard measures and where price is determined through bargaining, as in most African markets. This paper describes a methodology developed in Ghana in which panels of experienced maize traders priced prepared maize samples showing different levels of insect damage. The relative price of damaged maize was quite consistent across the markets studied. Of the grain characteristics evaluated, percent damaged and mould-discoloured grains was the most practical and reliable predictor of price. At harvest a 1% increase in damaged grains decreased price on average by 1%, but later more damage was tolerated as maize became more scarce.