Z. Petrova1*, Z. Zlatev2

1Dobrudzha Agricultural Institute, 9520 General Toshevo, Bulgaria
2Department of Plant Physiology, Faculty of Agronomy, Agricultural University, 12 Mendeleev, 4000 Plovdiv, Bulgaria

Abstract. The aim of this investigation was to determine the effect of the date of application of a set of herbicides on the foliar gas exchange of common winter wheat. The investigations were carried out in 2013 and 2014 at Dobrudzha Agricultural Institute (DAI). 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) and Husar Мax ОD (1000 ml/ha) from the group of suflonylureas with various mechanism of action. The preparations were applied at two stages of common winter wheat cultivars Aglika and Enola (stages 29 and 32 according to Zadoks). The indices of leaf gas exchange were followed: rate of net photosynthesis (А), intensity of transpiration (E), stomatal conductivity (gs) and intercellular concentration of СО2 (ci). It was found that the later application (stage 32) of Lintur 70VG and Mustang 306.25СК caused visible signs of phytotoxicity. These were expressed as anthocyanin pigmentation of leaves and spikes and as partial to full sterility of spikes, stronger after using Lintur VG and weaker after Mustang 306.25СК. Following a delayed application of the herbicides, slower rate of growth of plants was observed, as well as disturbances in the parameters of foliar gas exchange. The high rate of A at comparatively low E and gs and the low ci in the weeded check indicated that the plants spent considerable energy resources to overcome the negative effect of weeding.