Population of Meloidogyne incognita were evaluated in the soil and by biotesting. The population fluctuation of M. incognita was also studied during the beans (Phaseolus vulgaris) life cycle. Two days after the treatments in the field, plowing, without irrigation was found to be the most efficient in reducing J2 population (P<0,01), followed by plowed-irrigated plots. The soil inoculum infectivity, however, was lower (P<0,01) in plowed-irrigated plots than in plowed soil only. At 14 days, the lowest (P<0,01) J2 population was observed in plowed-irrigated plots, followed by plowed soil. The infectivity at 14 days was different (P<0,01) for all treatments, but lowest (P<0,01) in plowed-irrigated plots. At 45 days after bean planting in the field, the J2 population in soil was, also, different (P<0,01) for all treatments, but still the lowest (P<0,01) in plowed-irrigated soil 14 days before seeding. At 90 days, in the field, the numbers of eggs and egg-masses per bean plant, and the numbers of J2 in the soil were also the lowest (P<0,01) in plowed-irrigated plots. The root and shoot weight of field bean in plowed and plowed-irrigated plots were equally (P<0,01) high, but higher (P<0,01) than in control and in only irrigated plots. Crop yield was different in all treatments (P<0,01). The greatest (P<0,01) bean yield occurred in plowed-irrigated plots 14 days before seeding with an increased productivity of four times compared to the control. Irrigation as a way of increasing effectiveness against plant parasitic nematodes has been previously postulated but never proved experimentally, as it was accomplished in this work.
