The effect of the term of application of growth regulators on selected traits of winter wheat

In 2017/18 and 2019/20, experiments were established with growth regulators containing the active substances trinexapac-ethyl, chlormequat chloride and ethephon in the winter wheat variety AF Jumiko susceptible to lodging. The effect of growth regulators in the maximum allowed doses applied in the recommended terms (RT) was monitored, in comparison with the maximum and reduced doses applied after the recommended terms (RT) on selected features (canopy height, lodging, grain yield, thousand kernel weight). In the average of the experimental years, the Retacel (1.0 l) + Moddus (0.2 l) tank mix in RT and after RT had the strongest effect on the shortening of the canopy, the level of lodging in 2020 was most markedly reduced by Moddus (0.4 l in RT and after RT) and the least by Retacel (1.5 l in RT and 1.5 l and 0.8 l after RT). In 2018, with low density and short non-lodging canopy stressed by high temperatures and drought, growth regulators either did not affect the grain yield or caused it to decline. An exception was Retacel (1.5 l) applied in RT. In this case the grain yield was increased slightly. In 2018 all regulators reduced thousand kernel weight. On the contrary, in 2020, with dense and high lodged canopies in wet and cold weather, the use of growth regulators led to a reduction in lodging and, despite a smaller effect on shortening the canopy, to an increase in grain yield. The highest grain yield levels were achieved in 2020 by the tank mix Retacel (1.0 l) + Moddus (0.2 l), and the variant Moddus (0.2 l) and Cerone (1.0 l) in the maximum allowed dose, both variants in RT. In both years, the applications of growth regulators after RT led to lower grain yields compared to the applications on RT. Reduced doses of regulators applied after RT shortened the canopy less, in case of lodging they lodged more than the maximum allowed doses after RT.