The effect of netted scab (Streptomyces spp.) and Verticillium dahliae on growth and yield of potato

The effect of Streptomyces spp. (netted scab) on the growth of potato was investigated in three pot experiments, in two of which the effect of Verticillium dahliae was also assessed. The netted scab organisms attacked all underground plant parts of susceptible potato cultivars early in the growing season; the roots were especially seriously attacked, markedly reducing tuber yield and number but prolonging the duration of the growing season. The nematicide oxamyl had little effect on the incidence of netted scab. Repeated growing of the susceptible cv. Bintje greatly increased soil contamination with the netted scab pathogens. V. dahliae reduced haulm growth before wilt symptoms were evident and it reduced tuber yield but not number. Oxamyl delayed infection by V. dahliae by controlling parasitic Pratylenchus nematodes (mainly P. thornei).