Effect of Initial Nematode Density on Managing Globodera rostochiensis with Resistant Cultivars and Nonhosts.

Cropping systems in which resistant potato cultivars were grown at different frequencies in rotation with susceptible cultivars and a nonhost (oats) were evaluated at four initial nematode population densities (Pi) for their ability to maintain Globodera rostochiensis at a target level of <0.2 egg/cm(3) of soil. At a Pi of 0.1 to 1 egg/cm(3) of soil, cropping systems with 2 successive years of a resistant cultivar every 3 years of potato production reduced and maintained G. rostochiensis at <0.2 egg/cm(3) of soil. At a Pi of 1 to 4 eggs/cm(3) of soil, 2 successive years of a resistant cultivar followed by 1 year of oats for every 4 years of production were necessary to reduce and maintain G. rostochiensis populations at <0.2 egg/cm(3) of soil. At a Pi greater than 4 eggs/cm(3) of soil, 2 successive years of a resistant cultivar plus 1 year of oats reduced G. rostochiensis densities to <0.2 egg/cm(3) of soil, but the population increased above that density after cropping 1 year to a susceptible cultivar. The numbers of cysts and eggs per cyst in the final population (Pf) of G. rostochiensis were influenced by initial density and the frequency of growing a susceptible cultivar in a cropping system. The lowest number of cysts and eggs per cyst in the final G. rostochiensis population occurred with a cropping system consisting of 2 successive years of a resistant cultivar followed by oats with a susceptible cultivar grown the fourth year of production.