Plant parasitic nematodes are an increasing threat to organic farming in Germany. Especially taxa with broad host spectra and high multiplication rates such as Meloidogyne hapla and Pratylenchus spp. can cause severe damage up to total loss of the crop. The control of these nematodes is extremely difficult. Resistant cultivars are not available and only few non-host crops are known. Weed control is another important issue as most weeds are excellent hosts. In 2003 and 2004 two on-farm trials aimed at controlling M. hapla and Pratylenchus spp. were conducted in Niedersachsen, Germany. Results from these trials can be summarized as follows. For M. hapla, best control was achieved with black fallow and maize in combination with weed control. Fodder radish 'Siletina' grown as trap crop and fodder radish 'Commodore' inhibited population increase of M. hapla. Clover/grass-mixtures and fodder radish 'Siletina' increased population densities of M. hapla. Regarding Pratylenchus spp., all treatments increased the nematode population; however, population increase was less pronounced for black fallow, fodder radish 'Siletina' grown as trap crop and clover/grass-mixture
