Modern insecticidal protection of peas against major pests in the conditions of the Ukrainian Steppe

Abstract

The purpose of the article is to determine the economic and biological (technical) effectiveness of modern insecticides for spraying pea seedlings in order to limit the number of bulb weevils in crop crops. Research methods. A set of general scientific methods and approaches of empirical and theoretical knowledge was applied: abstract-logical, statistical, modeling, generalization. Research results. Protection of pea crops from pests is based not only on agrotechnical, biological, economic and other measures, but also on the use of chemical preparations, which are an integral part of integrated crop protection systems. Taking into account the biological characteristics and seasonal dynamics of the number of tuber weevils (Sitona spp.), one of the most effective preventive measures is pre-sowing treatment of pea seeds in order to protect seedlings from imagoes of these phytophagous insects. It was found that seedling pests were effectively controlled by pre-sowing seed treatment with modern systemic insecticides Nominal Ultra (thiamethoxam, 350 g/l) at a rate of 6.0 l/t and Greenfort Confi (imidacloprid, 500 g/l) at a rate of 2.0–2.5 l/t in combination with the fungicidal insecticide Greenfort KT 170 (carboxin + thiram) at a rate of 6.0 l/t. The plant damage coefficient on these variants on the 7th day after emergence was 0.34–0.41, while in the control it reached 1.48–1.56. A somewhat higher level of seedling damage was observed in the variants with the use of only imidacloprid-containing insecticides, however, the percentage of damaged plants and the integral indicator of harmfulness remained 2.5–3.0 times lower than in the untreated control, which indicates the high biological effectiveness of modern systemic insecticides for pre-sowing protection of peas from tuber weevils. Seed treatment with the studied insecticides provided not only a biological, but also a clearly expressed economic effect. The yield of pea grain in the variants with insecticides increased by 0.33–0.53 t/ha compared to the control, which corresponded to an increase of 12.8–20.6 % depending on the drug and the year of the studies. The highest yield indicators were obtained in variants with the use of thiamethoxam-containing insecticide, where the survival of plants at the early stages of development was combined with an increased number and functional activity of nodules, which contributed to the intensification of symbiotic nitrogen fixation and improved nitrogen nutrition of the crop. Analysis of the yield structure showed that the increase in yield was formed by increasing the density of the productive stem, the number of beans per plant and the weight of 1000 grains, which indicates a complex positive effect of insecticidal treatment on the formation of pea productivity elements. Conclusions. In the steppe zone of Ukraine, nodule weevils (Sitona spp.) are dominant and economically dangerous pests of pea seedlings, the number of which during the years of research consistently exceeded the economic threshold of harmfulness, which caused a significant decrease in plant survival and damage to nitrogen-fixing nodules. It was established that pre-sowing treatment of pea seeds with modern systemic insecticides – Nominal Ultra (thiamethoxam, 350 g/l) at a rate of 6.0 l/t and Greenfort Confi (imidacloprid, 500 g/l) at a rate of 2.0–2.5 l/t in combination with the fungicidal treatment agent Greenfort KT 170 (6.0 l/t) – provides a high level of protection of seedlings from imago and larvae of tuber weevils during the most vulnerable phases of crop development. The biological effectiveness of treatment was manifested in a 2.5–4.5-fold reduction in damage to seedlings compared to the control and a reduction in the proportion of damaged tubers from 65.5 % to 11.1–20.5 %, which contributed to the preservation of a functionally active symbiotic apparatus and an increase in the level of nitrogen fixation. The economic effect of the use of insecticidal treatments was confirmed by a significant increase in pea grain yield by 0.33–0.53 t/ha (14.8–25.4 %) with the formation of the highest indicators – 2.41–2.61 t/ha, which was due to an increase in the density of the productive stem, the number of beans per plant and the weight of 1000 grains. Thus, pre-sowing treatment of pea seeds with systemic insecticides is an agronomically feasible, economically effective and environmentally sound element of an integrated system of crop protection against tuber weevils in the steppe conditions of Ukraine and is recommended for widespread introduction into production.