The objective of this study was to determine the periods of weed interference in sunflower cultivation, and its effects on the head diameter, oil content, oil yield and its productivity. The experimental design was in the randomized blocks with three replications. The treatments were arranged in a factorial 2 x 2 x 5, with the following factors: cultivar (Embrapa 122 and Hélio 358), modality of competition (in the presence and absence of weeds) and periods of coexistence and control of weed from the emergence until the 15, 30, 45, 60 and 110 days. The measured variables were head diameter, oil content, oil yield and productivity. Weeds interfere negatively in the head diameter, in the productivity, and in the yield of oil, but the coexistence with the weeds increases the oil content of seeds, as well as reduces in 76.83 and 92.68% the productivity of cultivars Embrapa 122 and Hélio 358, respectively. Assuming a 10% loss in productivity, the PAI, PTPI and the critical period of prevention and interference (PCPI) for the cultivar Embrapa 122 were 16, 37 and 21 days, respectively. For the hybrid Hélio 358 the period before interference (PAI), the PTPI and the PCPI were 24, 43 and 19 days, respectively.
Helianthus annuus L.; interspecific competition; model Boltzmann sigmoidal
