Glasshouse experiments were conducted to evaluate the effect of initial population densities (Pi) of Ditylenchus destructor and D. dipsaci on potato tuber damage and nematode reproduction. Ditylenchus destructor did not influence tuber numbers but influenced tuber weight at high Pi levels. Ditylenchus dipsaci influenced tuber numbers and weights at a Pi level of 14.29 (g growing medium)−1. Tolerance limit estimates according to the Seinhorst model were very low indicating both nematode species have a major impact on potato tuber weight. External and internal tuber rot caused by both species increased with Pi levels. Ditylenchus destructor caused more tuber rot than D. dipsaci at all Pi levels. Reproduction rates of D. destructor were higher at all Pi levels studied compared to D. dipsaci. The equilibrium density of 1.3 and 0.6 for D. destructor and D. dipsaci, respectively, was observed at Pi level of 14.29 (g growing medium)−1.