Influence of chemical fungicides on amount of soil micromycetes in spring rapeseed agrocenosis in the central zone of the Krasnodar region

Different soil fungi infect many agricultural crops. They cause infectious diseases of plants and can be a serious threat for crop yield that leads to significant losses in the agricultural economics all over the world. Currently, a chemical method of Brassicaceae oil crops protection is the most spread. An important technique of this method is pre-sowing seed treatment decreasing a level of internal and external infections. Fungicides must be both effective against diseases and environmentally friendly. Currently, there is no unequivocal opinion how the chemical fungicides influence on soil microflora. The purpose of the research was to study impact of some seed protectants on an amount of suppressor fungi from species Trichoderma Pers. and pathogenic fungi from species Fusarium Link. in soil in spring rapeseed agrocenosis. The research was conducted at the V.S. Pustovoit All-Russian Research Institute of Oil Crops in 2020-2022. Before sowing, the seeds were treated with protectants with active ingredients: thiram, WSC (400 g/l) (etalon), carboxin + thiram, WSC (200 + 200 g/l), imazalil + tebuconazole, OE (100 + 60 g/l), and fludioxonil, SC (25 g/l). Soil was sampled before planting of treated rapeseed seeds and in crop phases of 2-4 true leaves and yellow pods. The soil layer from 0 to 10 cm was studied as it contains the most amount of lateral roots of this crop. To the rapeseed maturation, amounts of suppressor fungi in variants with application of preparations was at the level of the control; it increased by 1.8-2.4 × 103 CFU/g and reached 7.3-8.0 × 103 CFU/g, maximal meaning was in variant with an active ingredient fludioxonil (25 g/l). The amount of pathogenic micromycetes Fusarium spp. was by 1.7-2.0 times lower the control to the rapeseed maturation in variants with application of preparations.