Sunflower hybrids were tested for their proneness to diseases and how they are able to realise their yield potential in the case of different climatic circumstances and sowing dates in a special experiment (without fungicide treatment) in various growing years in 2009, 2010 and 2012. The field experiment involved two sunflower hybrids of different genotypes (NK Neoma, PR64H42) and three sowing dates (early, average, late) and it was established at the Látókép Experiment Site of the University of Debrecen, Centre for Agricultural and Applied Economic Sciences, Faculty of Agricultural and Food Sciences and Environmental Management. The weather circumstances of the examined growing years strongly influenced the extent of the appearance of and damage done by pathogens. There has been significant difference between the three growing years in the extent of infection. The drought-stricken year of 2009 was not favourable for either Sclerotinia or Diaporthe. In 2012, both pathogens caused more significant infection in comparison to the dry growing year (2009) (Sclerotinia: 69.4%, Diaporthe: 71.4% higher infection rate averaged of over hybrids and stems than in 2009). The large amount of precipitation in 2010 created favourable conditions for pathogens; therefore, the infection in sunflower populations was especially high (averaged over hybrids depending on sowing date: Sclerotinia: 7.0–29.0%, Diaporthe: 38.0–89.0%). In addition to climatic conditions, different sowing dates also significantly affected the level of infection in the examined populations. During our examination, the level of Sclerotinia and Diaporthe infection decreased by protracting sowing dates. The weather circumstance of the examined growing years also determined the yield and optimal sowing dates of the tested hybrids. Averaged over the examined hybrids and sowing dates, identical yields were obtained in 2009 and 2012 (2009: 3781 kg ha-1, 2012: 3764 kg ha-1) despite the fact that there were significant differences in the level of infection within the population. The especially high infection levels in 2010 were also shown in yield data. Yield was lower than in both 2009 and 2010 (by 16.3% and 16.0%). Averaged over the examined hybrids, the optimal sowing date was the average sowing date both in 2009 (4249 kg ha-1) and 2010 (3539 kg ha-1), while it was the late sowing date in 2012 (4196 kg ha-1). Total three growing years, the lowest yield was obtained in the case of the early sowing date. In nearly all cases, there were significant differences between the yields of the two hybrids. NK Neoma had the highest yield (4772 kg ha-1) in the case of the late sowing date in 2012, while PR64H42 produced the highest yield in 2010, when average sowing date was used (4487 kg ha-1). Pearson’s correlation analysis was performed to examine the interaction between the various factors. It was concluded that protracting the sowing dates reduced the Sclerotinia and Diaporthe infection levels (r=-0.428**, r=-0.563**) in the examined growing years. Yields were slightly affected by sowing dates and the Sclerotinia and Diaporthe infection levels (r=0.274*, r=-0.488**, r=-0.396**).

Keywords: sunflower, sowing date, genotype, yield