Intercrops, Cicadulina spp., and maize streak virus disease

Intercrops of bean and finger millet were tested as a possible means of con trolling maize streak virus disease (MSVD) in maize by disrupting the matin g behaviour of the insect vectors of the maize streak virus, Cicadulina mbi la and C. storeyi. A series of three trials were done. In the first, MSVD i ncidence 2 months after sowing was reduced to 14.9% and 17.4% in millet and bean intercrops compared to 29.5% in the pure maize stand. The number of m ale Cicadulina spp. caught on sticky pole traps was also significantly redu ced relative to the control, but there was little effect on the catch of fe males. There was no significant yield penalty for the millet intercrop but maize yield was 49% lower in the bean intercrop treatment than in the pure stand. In the second trial, there were two millet and two bean intercrop tr eatments and a maize only control. Fewer male Cicadulina spp. were caught i n the intercrop treatments relative to the control but MSVD incidence was r educed in one millet intercrop treatment only for which the associated maiz e yield penalty was 89%. In the final trial the bean intercrop was again te sted but it had no effect on MSVD incidence. These experiments demonstrated that intercropping maize with bean or millet decreased vector activity and /or vector numbers. Vector catches were predominantly male, and catches of males but not females were reduced in the intercrop treatments compared wit h pure stands. However the lower vector catch was not consistently associat ed with a significant reduction in MSVD incidence, and when it was there wa s often an associated yield penalty in the maize due to the intercrop.