Evaluating the problem of spotwise appearing cereal growth depressions 23 fields of 10 organic managed farms were investigated. Potential causes were soil nutrients and other chemical and physical soil properties as well as high abundance of the plant parasitic nematodes Heterodera avenae and Pratylenchus-, Tylenchorhynchus and Trichodorus species. In two on-farm field experiments different catch crops and a black fallow treatment caused a decrease of Pratylenchus and Tylenchorhynchus species. However, the yields of the following spring wheat were low, possibly due to H. avenae infestation. Fertilization with compost and potassium had no effect but the H. avenae resistant variety Isotta produced much higher yields. The conclusion drawn was that farmers with spotwise appearing growth depressions should watch them closely for nematode infestation to take regulation measures as early as possible
