Short- and long-term response of sunflower to airborne bromoxynil-octanoate under controlled and field conditions.

Wind tunnel studies and a field study were conducted to investigate the impact of the airborne herbicide bromoxynil-octanoate on non-target plants. Sunflowers at the two-leaf stage were used as test plants and exposed for 24 h in a wind tunnel to a range of concentrations of airborne bromoxynil-octanoate. Quantum yield of electron transport at Photosystem II (phiPSII) of exposed leaves and leaves developed after exposure, plant height, days to flower and head diameter were used to determine the short- and long-term response of sunflowers to bromoxynil-octanoate. Quantum yield of exposed leaves and of the second leaf pair, determined 1 h and 2 days after exposure, was reduced at concentrations >0.449 and >1.159 microg/m3, respectively, but no effects on further leaf pairs developed after exposure were observed. Growth parameters were partly affected when exposed to >1.448 microg/m3. In a field study a maize plot was treated with bromoxynil-octanoate and parathion-methyl, used as a tracer compound. Afterwards, potted sunflowers were placed inside the maize plot and at different distances (2, 4, 8 and 16 m) from the treated plot. The highest concentrations of bromoxynil-octanoate and parathion-methyl collected in air samples at a distance of 8 m outside of the treated plot were 0.100 and 0.055 microg/m3, respectively. Little of the breakdown product bromoxynil phenol was detected in the air. Detectable concentrations of bromoxynil-octanoate and bromoxynil phenol were found only in a few leaf samples, whereas parathion-methyl was detected in almost 50% of the leaf samples up to 16 m from the treated plot. Quantum yield and growth of sunflower were not affected due to low concentrations of bromoxynil-octanoate in the air.