INFLUENCE OF MAIZE ROW SPACING ON INFESTATION AND DAMAGE OF INTERCROPPED BEANS BY THE BEAN APHID (APHIS-FABAE SCOP) .2. REDUCTION IN BEAN YIELDS

Field studies were conducted to assess the effects of intercropping common beans (Phaseolus vulgaris L.) with maize (Zea mays L.), at two growth stages and four row spacings (0.5, 1.0, 1.5 and 2.0 m), on Aphis fabae infestation of beans and on the magnitudes of bean yield losses due to aphid attack and to competition by maize. The first maize planting (Old maize) was carried out 3 weeks earlier than beans, while the second planting (Young maize) was done simultaneously with beans. Significantly (P<0.05) fewer plants were infested by A. fabae when beans were intercropped with older or densely planted maize. Aphid colonies on beans were also smaller, and there was reduced aphid damage to beans in the intercrops. However, whereas bean yield loss from aphid attack was less than 3.5% in all intercrop situations, yield loss from competition by maize was very high, being up to 98% when beans were intercropped with early-planted maize at 0.5-m row spacing. Yields of intercropped maize planted at row spacings of 0.5, 1.5 and 2.0 m were also depressed. The results show that both maize growth and row spacings could be exploited for the control of A. fabae on intercropped beans. However, adequate consideration must be given to the negative effects of maize planting density and growth on yields of both crops.