Crop density affects weed suppression in organically managed Sunflower

A field experiment in central New York evaluated the effect of sunflower (Helianthus annuus L.) density on weed biomass and yield in organic sunflower production. Two varieties of sunflower, Badger DMR and N5LM307, were seeded at 6.1 and 8.6 seeds m−2, and grown using organic management practices at one site in 2016 and two sites in 2017. Sunflower density, weed biomass, and sunflower yield were quantified at crop maturity. Weed biomass was lower (P < .05) in plots with sunflower seeded at 8.6 seeds m−2 compared to 6.1 seeds m−2 in only one variety in one site-year. However, a negative relationship (P < .05) was observed between sunflower density and weed biomass when data were pooled over site-years. No difference was observed in sunflower seed yield between varieties or seeding rate treatments. Sunflower seed yield was higher in 2016 (354 g m−2) when conditions were extremely dry, and in one site-year in 2017 (308 g m−2), when conditions were extremely wet and seeding was delayed by a month. In the other site-year in 2017, sunflower seed yield was lower (225 g m−2), which was likely due to weed competition as weed biomass was an order of magnitude greater in this site-year than the other two site-years. Although more research is needed to refine management recommendations for organic sunflower production, our results suggest that increasing sunflower density can contribute to weed suppression