Relationships between cassava root yields and crop infestations by the mealybug,Phenacoccus manihoti

Abstract Reductions in cassava root yield were related to infestations of the crop by the cassava mealybug, Phenacoccus manihoti Mat.‐Ferr. in field trials that combined several varieties, dates of planting and dates of onset of infestation. Reductions in root yields of up to 84.4% and 54.4% were measured in late‐ and early‐planted cassava respectively. There was a gradual increase in yield loss due to pest attack with every delay in planting. Root yields for December, February and April plantings were reduced by 2.6, 11.2 and 31.2% respectively when compared with the first planting in October. However a delay in the onset of mealybug infestation results in a decrease in yield loss. A correlation coefficient of r = 0.77 was obtained between root yield and date of initial pest infestation. While peasant farmers are unable to offset early pest attacks on their crop, they can reduce crop damage by avoiding late plantings. In the absence of highly resistant varieties, cassava varieties that are able to offset early peaks in pest populations are recommended.