Effect of intercropping beans with maize on the severity of angular leaf spot of beans in Kenya

Angular leaf spot severity was evaluated on Phaseolus beans which had been planted alone (monocrop) and also simultaneously with maize (intercrop) at Kabete, Kenya, in November 1986 (short rains), and at Kabete and Thika in April 1987 (long rains). Intercropping reduced the area under the disease progress curve (AUDPC) in the short rains at Kabete and at Thika in the long rains by 23–33% at bean: maize proportions of 2:1 for some leaf positions, but did not reduce AUDPC significantly at Kabete in the long rains. Additional treatments to evaluate bean density and planting pattern (row against random) conducted in the short rains had no effect on AUDPC, although disease was reduced by 12–17% at higher bean densities when maize was not present. Fertilization increased AUDPC by 135–205% in the long rains at both sites. Microclimatological observations made at Kabete during the long rains indicated reductions in leaf temperature and air temperature, and increases in relative humidity, in most plots. These changes were small, averaging 0·6°C, 0·2°C, and 1·8%, respectively. Wind velocity was reduced by 55–63% in the intercrop in relation to the monocrop. The results reflect the variable response of angular leaf spot to maize intercrops seen in other studies.