Comparative assessment of the effectiveness of contact and systemic fungicides for treating soybean seeds in the forest-steppe of the Novosibirsk Region

Abstract

The study aimed to evaluate the biological and economic effectiveness of fungicidal soybean disinfectants of different mechanisms of action in a tank mixture with inoculants in the forest-steppe of the Novosibirsk region. The studies were carried out in 2019–2022. Generally accepted methods are used in the conditions of the northern forest steppe of the Novosibirsk region. For the studies, we used the systemic protectant Baritone (prothioconazole 37.5 g/l + fluoxastrobin 37.5 g/l) at a rate of 1.5 l/t and contact Maxim (fludioxonil 25 g/l) at a rate of 2.0 l/t t, the inoculant was HiCoat Super Soybean (HCSS) 1.42 l/t together with the nutrient medium HiCoat Super Extender (HCSE) 1.42 l/t. On average, over four years, the development of soybean root rots, according to the predecessor winter wheat, exceeded the harmfulness threshold in the control variant by 1.3–2.7 times over the years; the maximum indicator was noted in the dry year of 2022 when soybean plants experienced double stress - hydrothermal and biotic. F. oxysporum, F. poae, F. equseti, F. sporotrichioides, and F. solani were isolated from the underground soybean organs during the growing season. The pathogenic complex of soybean root rots also included fungi of the genera Pythium and Rhizoctonia. The biological effectiveness of seed treatment against root rot was 40.2–76.4% and was higher when soybean seedlings developed in moist conditions. The economic efficiency of seed treatment was 103–347% over the years, with a maximum in wet years. The best option for pre-sowing seed treatment is the contact disinfectant Maxim, 2.0 l/t in a tank mixture with the inoculant HiCoat Super Soya (HCSS), 1.42 l/t together with the nutrient medium HiCoat Super Extender (HCSE), 1.42 l/ T. Both fungicidal disinfectants showed a bactericidal effect on symbiotic nitrogen-fixing bacteria, reducing the number of nodules to 43.2% and their weight to 38.1%. Treatment and vaccination of soybean seeds positively affected the quality of the resulting crop. The protein content was the highest in the Baritone variant together with the inoculants HCSS + HCSE and amounted to 41.4% versus 36.8% in the control. Dressing agents had a significant positive effect on the quality of soybean seeds of the new crop; the best aftereffect was found in the Maxim variant, 2.0 l/t + inoculants, where the prevalence of all phytopathogens was below the ETH (economic threshold of harmfulness), and germination was maximum.