The effects on spring wheat (Triticum aestivum L., cv. Mario) of nine isolates of the Gaeumannomyces/Phialophora complex, ranging from non-pathogenic to pathogenic, were studied under different conditions of soil moisture, soil temperature, and photoperiod in growth chambers which simulated different autumn weather conditions. The experimental conditions were based on data (e.g. temperature) from representative sites (loamy sand, Muencheberg, Northeast Germany) collected in the last three decades. The results of seedling inoculation tests for four nonpathogenic isolates were partly in agreement with results from field trials done over 4 years. One non-pathogenic G. graminis var. tritici isolate (G 33) increased consistently dry weight of shoots in the simulation, and grain yield in field experiments. For non-pathogenic isolates, warm temperatures with moderate soil moisture most often stimulated plant growth, with less effect in cold dry soil conditions. The decrease in seedling growth caused by pathogenic isolates was influenced only slightly by temperature changes, but was often enhanced by increased soil moisture.