In our experiment the reaction of six sunflower hybrids of different genotypes (NK Oktava, ES Biba, ES Diagora, ES Ballistic, EGH 8925, PR 64 H 42) towards plant density has been investigated by different fungicide treatments in the crop-year of 2011 on a chernozem soil. 
In the crop-year of 2011 sunflower populations were infected by a significant Diaporthe helianthi disease. The extent of this infection was significantly enhanced by the increment of plant density. However, regarding the average of the hybrids and plant densities the two times executed fungicide treatment has decreased the infection rate by 22%. The most susceptible hybrid was the ES Biba. Contrarily, the hybrid ECH8925 proved to be the most resistant hybrid towards this
disease according to our results. According to the results of the Pearson’s correlation analysis it has been revealed that stalk breakage and Diaporthe infection stand in a very close (r=0.782**) and middle close (r=0.523**) correlation resp. with plant density. The relationship between fungucude treatments and stalk breakage, just as Diaporthe infection showed to be middle and close respectively. Our results demonstrate the role of stalk and plate diseases (among them Diaporthe) in causing stalk breakage, for we have found a close positive correlation between stalk breakage and Diaporthe infection (r=0.624**) in our analysis.
From the aspect of yield amount the optimal plant density varied between 45 000 and 55 000 plants per hectare. Fungucude treatments enabled not only the use of higher plants densities, but they had a yield increasing effect as well. In the crop-year of 2011 the highest yield (4 559 kg ha^-1) on a chernozem soil has been measured in case of the hybrid ECH8925.