Problem statement. In Ukraine, the loss of legume crops caused by diseases of various etiologies is on average 15-20%, but the product shortages can reach 50% with epiphytic development. Since the infestation of plants with pathogens and the further development of the pathological process depend entirely on agro-climatic factors, the study of the development of the most common and harmful diseases of soybeans depending on agro-climatic conditions is relevant.
Analysis of recent research and publications. Studies of the leading phytopathologists of Ukraine indicate a further deterioration of the phytosanitary status of soybean crops due to crop damage by diseases [4,5,10]. Extensive management, unjustified chemicalization, impoverishment of crop rotations, climate change and other factors create extremely favorable conditions for pest infestation [1,8]. Agroclimatic conditions are decisive for the development of pathogens of soybean diseases.
Research methodology. The research was conducted according to the methods of research  at Ustymivska research station of crop production in Poltava region from 2016 to 2019.
The aim of the research was to determine the dependence of phytosanitary condition of soybean crops from agro-climatic conditions in order to optimize the use of agrochemicals, which will reduce the pesticide load on agrocenoses, increase their biological efficiency and competitiveness of the products.
Presentation of the main research material. The species composition of pathogens of soybean diseases significantly depended on the agro-climatic conditions of the growing season. The response of the varieties to infections was similar.
Among the crops, fungi of the genera Alternaria, Fusarium, and Septoria, and bacteria of the genus Pseudomonas were predominant.
According to the peculiarities of the biology of the pathogen causing fusarium wilt, the agro-climatic conditions of 2016 and 2019 were the most favorable for its development. The prevalence of the disease by varieties ranged from 2.8% to 5.2% (2016) and from 4.5% to 5.6% (2019). Increased development of fusarium wilt was observed in conditions that cause stress to plants.
The maximum prevalence of bacteriosis associated with warm humid weather was observed in 2019 in the flowering – beginning of the formation of beans phase (4.5-4.7%).
Significant prevalence of Alternaria was observed only in 2019. The infection increased during flowering – beginning of bean formation (13.5-25.5%) and ripening phases (18.5-22.7%); the intensity of the disease development did not exceed 9.5%. Droplet moisture is optimal for the pathogen. It is tolerant to temperature.
During the unfavorable for Septoria years of 2017 and 2018 (low humidity), the spread of infection was 1.9-3.3%, and the intensity of the disease did not exceed 2%. In 2016 and 2019, the prevalence of the disease during the flowering – beginning of formation of beans phase varied from 9.8 to 12.5%, and the maximum level was observed in the maturation phase – 18.7%. The intensity of Septoria development did not actually differ in the phases of ontogenesis.
Conclusions. The connection between the development and spread of diseases and hydrothermal environmental conditions has been identified.
The establishment of a correlation between the biology of pathogens and agro-climatic indicators allows to predict their development and to use pesticides only when necessary, which will reduce the pesticide load on agrocenoses, increase their biological efficiency and competitiveness of the crop products.
Keywords: soybean, alternariosis, septoria, fusarium wilt, bacterial burns, disease development, disease prevalence.
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