P. penetrans poses a problem for carrot production in both Germany and The Netherlands. Farmers have to meet the desired quality set by the canning industry. Currently, suitability of land for carrot production is based on an arbitrarily set pre-plant nematode density of 100 and 75 P. penetrans (100 ml)-1 of soil in both countries, respectively.
For yield loss prediction, one needs to establish the relation between nematode density and both -yield and quality loss. A glasshouse experiment, at varying seed densities of carrot cv. Nerac, at a large range of population densities, was carried out. P. penetrans caused more quality damage than yield loss. A tolerance limit for quality (Tq) and yield damages (Ty) of 0.4 and 1.6 P. penetrans (g dry soil)-1, respectively independent of seed density, was estimated. The quality damage threshold, approx. 50 P. penetrans (100 ml)-1 soil, deviated a little from the current standards. According to the population dynamics parameters, carrot cv. Nerac proved to be a good host for P. penetrans.