Control of Pratylenchus penetrans on Potato with Metam-sodium Applied in Irrigation Water.

In 1986, metam-sodium broadcast at 152, 76, 38, 19, and 9.5 kg a.i./ha suppressed the population density of 19,600 Pratylenchus penetrans/kg soil at planting by 100, 90, 63, 23, and 14%, respectively, and in 1987, with 1,370 P. penetrans/kg soil, by 99, 88, 57, 11, and 1%. At harvest, soil population densities increased 2.2-fold in 1986 and 13.9-fold in 1987. Rate of population increase was similar at all rates of nematicide except it was slower at 152 kg a.i./ha in 1987. In both years, shoot and root weights did not differ (P = 0.05). In 1986 the number of tubers in plots treated with 76 and 152 kg metam-sodium a.i./ha and the marketable tuber weight at the three highest rates did not differ significantly from the untreated control. However, 76 and 152 kg a.i./ha resulted in larger numbers of tubers relative to the three lowest rates of metam-sodium and in higher tuber weight relative to the two lowest rates. Yield differences were not statistically significant in 1987, probably because of low infestation levels.