Biological Justification for the Applicability of Herbicides at Different Stages of Cereal Crop Development

The biological and economic efficiency of the use of the new, combined herbicide Uniko, CSC, (100 g/L fluroxypyr + 2.5 g/L florasulam) at application rates of 1.0, 1.25, 1.5, and 1.75 L/ha is studied in field trials. Cereal crops were sprayed in three stages: tillering/early booting, flag leaf stage, and heading (the experiment using herbicides at the latest stage was performed in Russia for the first time). The trials were carried out according to the Guidelines for Registration Tests of Herbicides in Agriculture in 2016 and 2017. The use of 1.0 L/ha Uniko herbicide at early stages of cereal crop growth and development provided 66.4–83.4% of weed clearing. This was more effective than the use of 0.43 L/ha standard Demetra, EC. An increase in the application rate of the herbicide Uniko, CSC, led to an increase in its biological efficiency to 68.8–91.0% (1.25 L/ha), 72.4–95.3% (1.5 L/ha), and 76.5–97.3% (1.75 L/ha). The use of the maximum rate of standard Demetra, EC, (0.57 L/ha) proved to be less effective: the total weed infestation of cereal crops decreased by 62.4–86.7%. The advantage of the Uniko herbicide over the standard was that it had a stronger effect on weed species, such as Papaver rhoeas, Sonchus arvensis L., Cirsium arvense (L.) Scop., Chenopodium album L., and Amaranthus retroflexus L. Late treatments (at the flag leaf stage and, in particular, at the crop-booting stage) were generally less effective (up to 25%) than treatments at the tillering stage. Despite the decrease in the general efficiency of late treatments, they can be productive in some cases, taking into account the biological features of some weed species, as in the case of the late emergence of seedlings of Convolvulus arvensis L., for which the stage of its highest vulnerability to the effect of herbicides can fall on the crop-heading time. According to the study results, the herbicide Uniko, CSC, is recommended for use in the Russian Federation.