To Study the Effects of intercropping of maize with beans on weeds and plant diseases suppression in the Southern Highland region of Yemen, two intercropping experiments were carried out at Ibb experimental farm of the Southern Uplands Regional Agricultural Research Station, Yemen. The first experiment was conducted on two consecutive rainy seasons of 2003 and 2004 that included different ratio of intercropping with Randomized Complete Block Design (RCBD). The second experiment was conducted on Rabi season (January 2005) with Split Plot Design where the first factor was bean cultivars, the second factor was intercropping ratio and the third factor was intercropping spacing. Results showed strong relation in intercropping potential on suppression of weeds and diseases of Maize and Bean. It was found that as the Bean plant density increased and Maize plant density decreased the degree of maize infection with blight, spotting, virus and rust were decreased significantly; In contrast, as the Bean plant density decreased and Maize plant density increased the degree of bean infection with blight, spotting, virus and powdery mildew were decreased. In addition, it was observed that the weed dry weight increased as the intercropping spacing was increased and that the Bean local variety (Yemen-1) had shown higher competitive ability comparing to the variety (A-48). The efficient intercropping ratio was obtained from 1:1 Maize : bean ratio at spacing of 60 cm for the local variety (Yemen-1) and 50 cm for the variety (A-48). At this ratio and spacing, weed and disease were significantly depressed.

Key Words :Intercropping potential, suppression, blight, spotting, viruses, powdery mildew, weed dry weight