Modern sunflower hybrids have significant environmental sensitivity. The development of average and intensive agrotechnical models is becoming an increasingly urgent task which makes it possible to increase yield safety, while yield quantity and quality can also be improved.

Of the various agrotechnical elements, crop protection is significant in sunflower production, while the main sowing technological factors are crop density and sowing date. Optimal sowing technology and crop protection makes it possible to maximise the yield potential of hybrids.

The field experiment was carried out in the experimental crop production site of the Centre for Agricultural and Applied Economic Sciences of the University of Debrecen. Two hybrids were involved in the examinations in 2008-2009 (2008: NK Delfi, PR64D82; 2009: Petunia, NK Kondi) and one hybrid (NK Kondi) was examined in 2010.

The experimental plots were established with randomised block design and four replications. Three sowing dates (2008: 1st early sowing date: 29th March; 2nd optimal sowing date: 9th April; 3rd late sowing date: 4th May; 2009: 1st early sowing date: 31st March; 2nd optimal sowing date: 18th April; 3rd late sowing date: 5th May; 2010: 1st early sowing date: 26th March; 2nd optimal sowing date: 9th April; 3rd late sowing date: 3rd May) and four different theoretical plant numbers were used (35 000–65 000 plants per ha) in 10 000 plants per ha steps. The fungicide treatment of the experiment was performed at the 8 pair leaf stage on plots treated once and both at the 8 pair leaf and at the flowering stage on plots treated twice.

The agrotechnical and crop protection treatments in the experiment and the crop year effect strongly affected yield quantity and yield safety. Based on the average values of the three examined crop years, it can be established that crop year, population density, sowing date and the protection against fungal diseases act in correlation with each other – strengthening or weakening each other’s impact. In the wet crop year, maximum yield was obtained in the case of lower population density (35 000–55 000 plants per hectare), while yield was more favourable in the dry crop year if higher population density was used (55 000–65 000 plants per hectare). Fungicide crop protection made it possible to use higher crop density. In the wet crop year, the yield increasing effect of the one-time protection was higher than in the dry crop year. The yield increasing effect of the first fungicide treatment was more significant in 2008 (wet) and 2009 (dry) than the second treatment. In 2010, the significant amount of precipitation resulted in a high plant pathological pressure; therefore, the effect of both the first and the second fungicide treatment was shown to be significant. Based on the obtained findings, it was established that later sowing dates result in increasing yield in the rainy and extremely rainy crop years of 2008 and 2010. In 2009, drought in April resulted in lower yields in the case of the early sowing date in comparison with the optimal and late sowing dates. The highest yield was ontained in the optimal sowing date in the middle of April.

Keywords: sunflower, yield, plant number, sowing date, fungicide crop protection