Leaf harvesting effects on leaf retention and pest and disease incidence of cassava (Manihot esculenta Crantz)

Two field experiments were conducted in the 1996-97 crop season to investigate the effect of leaf harvest frequency on leaf retention and pest and disease incidence on cassava genotypes, at two sites in the derived (Ibadan) and southern Guinea savannah (Mokwa) zones of Nigeria. Four leaf harvest frequencies (one-, two-, and three-monthly intervals, and no harvest) were imposed on each genotype. The effects of genotype, harvest frequency, and their interaction were highly significant for the number of leaves retained at the peak dry season at both sites. Generally, as the intensity of leaf harvest increased, the number of leaves retained decreased. Genotype and frequency of leaf harvest significantly affected African cassava mosaic virus disease (ACMVD) at Mokwa with the intensity increasing as harvest frequency increased. For cassava bacterial blight (CBB) harvest frequency effect was significant. Monthly and two-monthly frequencies had the highest CBB infection. Effects of genotype and harvest frequency were highly significant for cassava green mite (CGM). Generally, as leaf harvest intensity decreased, CGM damage increased, with no-leaf harvest incurring the highest damage and the monthly harvest treatment the lowest.