The Critical Period of Weed Control Influences Sunflower (<i>Helianthus annuus</i> L.) Yield, Yield Components but Not Oil Content
Edita Stefanic,
Sanda Rasic,
Pavo Lucic,
Domagoj Zimmer,
Anto Mijic,
Slavica Antunovic,
Bozica Japundzic-Palenkic,
Marin Lukacevic,
Dinko Zima,
Ivan Stefanic
Affiliations
Edita Stefanic
Faculty of Agrobiotechnical Sciences in Osijek, Department of Plant Medicine, J.J. Strossmayer University in Osijek, 31 000 Osijek, Croatia
Sanda Rasic
Faculty of Agrobiotechnical Sciences in Osijek, Department of Plant Medicine, J.J. Strossmayer University in Osijek, 31 000 Osijek, Croatia
Pavo Lucic
Faculty of Agrobiotechnical Sciences in Osijek, Department of Plant Medicine, J.J. Strossmayer University in Osijek, 31 000 Osijek, Croatia
Domagoj Zimmer
Faculty of Agrobiotechnical Sciences in Osijek, Department of Agromachinery and Renewable Energy Resources, J.J. Strossmayer University in Osijek, 31 000 Osijek, Croatia
Anto Mijic
Agricultural Institute Osijek, Južno Predgrađe 17, 31 000 Osijek, Croatia
Slavica Antunovic
Biotechnical Department, University of Slavonski Brod, Trg I. B. Mažuranić 2, 35 000 Slavonski Brod, Croatia
Bozica Japundzic-Palenkic
Biotechnical Department, University of Slavonski Brod, Trg I. B. Mažuranić 2, 35 000 Slavonski Brod, Croatia
Marin Lukacevic
Faculty of Agrobiotechnical Sciences in Osijek, Department of Plant Medicine, J.J. Strossmayer University in Osijek, 31 000 Osijek, Croatia
Dinko Zima
Faculty of Tourism and Rural Development in Pozega, J.J. Strossmayer University in Osijek, 34 000 Pozega, Croatia
Ivan Stefanic
Faculty of Agrobiotechnical Sciences in Osijek, Department of Bioeconomy and Rural Development, J.J. Strossmayer University in Osijek, 31 000 Osijek, Croatia
Field studies were conducted in the northeastern part of the Republic of Croatia to determine the influence of the critical period of weed interference on sunflower (Helianthus annuus) yield, yield components, and oil content. For this purpose, different durations of competition were established, allowing weeds to infest the crop for increasing periods of time after planting or maintaining plots weed-free for increasing periods of time after planting. The beginning and the end of the critical period of weed control (CPWC), based on a 5% and 10% loss of sunflower yield, were determined by fitting the four-parameter log-logistic equations to the relative seed yield. The total weed biomass increased progressively in relation to the increase in the competition. The beginning of the CPWC period, based on a 5% acceptable yield loss, ranged from 141 to 234 growing degree days (GDD), which corresponded to the two-to-four true leaf development stage (the V2–V4 growth stages) across both sites and years. The crop had to be kept weed-free until a period when sunflower inflorescence began to open and flower (the R4–R5 growth stage) or from 1365 to 1932 GDD. The sunflower yield and yield components varied between the years and among locations. An increasing duration of weed interference negatively affected crop height, head diameter, and 1000-kernel weight, but not seed oil content.