The aim of the investigation was to determine the effect of weed infestation and the date of application of a set of herbicides on the functional activity of the photosynthetic apparatus according to the parameters of the chlorophyll fluorescence of common winter wheat. The investigations were carried out during 2013–2014 at the Dobrudzha Agricultural Institute. The following herbicides were used: Derby super VG (33 g/ha), Granstar 75DF (15 g/ha), Lintur 70VG (150 g/ha), Secator ОD (100 ml/ha), Mustang 306,25 СК (800 ml/ha), Palace 75WG + oil (250 + 1000 g/ml/ha), Husar Max ОD (1000 ml/ha) from the group of sulfonylureas with various mechanism of action. The preparations were applied in two stages of the common winter wheat cultivars Aglika and Enola (stages 29 and 32 according to Zadoks). The indices of chlorophyll fluorescence were as follows: zero (minimum) chlorophyll fluorescence in dark-adapted leaves (F0), maximum fluorescence in dark-adapted leaves (Fm), maximum photochemical efficiency of PS2in dark-adapted leaves (Y0), moment chlorophyll fluorescence in light-adapted leaves (F`), maximum fluorescence in light-adapted leaves (F`m), actual photochemical efficiency of PS2 in light-adapted leaves (Y) and electron transportation rate in light-adapted leaves (ETR). The results from the analysis showed that the treatment with the herbicides did not have negative effect on the potential photosynthetic activity of PS2 in all variants of the two cultivars on both dates of application. The data from the light-adapted leaves in stage 32 revealed a decrease in the values of the actual photochemical efficiency (Y) and lower rate of electron transportation (ETR) after the use of Derby super VG, Lintur 70VG, Husar Маx ОD, Secator ОD and Mustang 306,25 СК in the Aglika cultivar. In the Enola cultivar, the factor “stage” was of a better statistical significance compared with the ETR factor, which was characterized by a lower effect according to the Yindex (0,096*).
Changes in the Chlorophyll fluorescence of common winter wheat depending on the weed infestation and the date of application of a set of herbicides