Effect of Nonhost Cultivars on Heterodera schachtii Population Dynamics.

Broadcast plantings of nonhost cultivars (alfalfa, barley, bean, onion, potato, and wheat) in soil in redwood boxes (4.2 x 30 x 14 cm) infested with Heterodera schachtii reduced the initial nematode populations (P = 0.05). The reduction was greater with sugarbeets, a host, than with all other cropping treatments except onion, bean, and fallow (P = 0.05). After 80 days, when the root growth of all treatments had completely penetrated the soil, the nematode population was lower under onion than under wheat and barley (P = 0.05). The terminal nematode population (160 days) was lowest under onion, followed by bean, potato, fallow, and alfalfa. The nematode population was less under onion than under fallow, alfalfa, barley, and wheat (P = 0.05). Bean, potato, and fallow nematode populations were less than barley populations (P = 0.05). When broadcast plantings of these cultivars were simulated in microplots, the terminal population (100 days) was significantly lower under onion and bean than fallow (P = 0.05). However, no significant differences in reduction of H. schachtii population density were obtained when commercial row plantings of these crops were simulated in microplots. H. schachtii suppressed growth of barley, tomato, and sugarbeet, but not of bean, onion, alfalfa, or wheat in the greenhouse. Only the growth of sugarbeet was suppressed significantly in the field (P = 0.05).