Reduction of potato scab, verticillium wilt, and nematodes by soymeal and meat and bone meal in two Ontario potato fields

Abstract

Soymeal (SM) and meat and bone meal (MBM) were incorporated into soil to a depth of 15 cm at a rate of 37 t/ha at two commercial potato (Solatium tuberosum) fields in Ontario in the spring of 1996. The incidence of verticillium wilt and potato scab, the population of plant parasitic nematodes, and the soil chemistry and microbiology were monitored in three subsequent crops of potatoes in 1996-1998. Verticillium dahliae microsclerotia (MS) were buried in the soil immediately after incorporation of the amendments, both in the field and in a concurrent laboratory assay using soil from the field placed in test tubes, and the viability of the MS was determined 4 weeks later. Both treatments reduced the incidence of verticillium wilt, potato scab, and the nematode population to near zero levels in 1996. Reduced disease levels were still evident in the 1997 crop, but by 1998, disease levels were equal to or higher than those in the control treatments. Nematode numbers remained below control levels for the 3 years of this study. Yields were significantly reduced in treated plots in the first year but because tubers were scab free, the marketable yield did not differ from the control plots. In the second year, total yields were higher in treated plots but the increase was significant from the control only with MBM at one site. The overall population of soil bacteria increased 100-fold immediately after the addition of SM and MBM and returned to control levels by the end of the first season. There was an initial elevation of soil pH from 6.0 to 8.5 at both sites and a corresponding increase in ammonia levels 2 weeks after incorporation. Nitrite and nitrate levels were also higher than those of the control treatments after 4 weeks. SM and MBM reduced MS viability by 72-100% of the control treatments at both sites, which was positively correlated with the incidence of verticillium wilt of the crop in the first season (r = 0.9, P < 0.0001). Thus, the V. dahliae MS bioassay, in conjunction with the laboratory assay, predicted the efficacy of these amendments for reducing verticillium will in the field.