Onion stemphiliosis in the South of Ukraine

Abstract

Onion stemphiliosis is a relatively new disease in Ukraine, so a deeper study of Stemphylium, the species composition of the pathocenosis, and isolation and determination of the species belonging of pathogens of the disease are relevant. The purpose of the study was to examine the species composition of pathocenosis, the biofenology of the causative agent of stemphiliosis, and determine the effectiveness of fungicides for further control of stemphiliosis in onion crops. The main research methods were: field – to determine the spread, development, and harmfulness of stemphiliosis; laboratory – to examine pathogens of onion diseases; visual and mathematical – statistical. The method of mycological crops on potato-dextrose agar (PDA) was used in the work. Field surveys in 2019-2021 established the spread and development of stemphiliosis in onion plantings in the Odesa District of the Odesa region. It was identified that the growing season of 2021 was the most favourable for stemphiliosis, when against the background of high humidity and air temperatures, the spread of the disease was 100%, and the development of the disease reached 79%. In onion crops, the disease developed unevenly, its spread was low in June, with rapid growth in July. At the beginning of August, the percentage of the disease reached 80%. Eight types of fungi were identified, of which Stemphylium vesicarium (Wallr.) Simm, Stemphylium botryosum Wallr, Stemphylium herbarum Simm. – are pathogens of onion stemphiliosis. Laboratory studies established the frequency of their distribution in samples. It is proved that five-time spraying with fungicides helps to reduce the further development of stemphiliosis in onion plantings. The high effectiveness of spraying plants with appropriate fungicides with the active substance fluopyram (200 g/l) + tebuconazole (200 g/l) and fluoxastrobin (100 g/l) + prothioconazole (100 g/l) to suppress the development of spores of pathogens is proven. The provisions and conclusions on the phytosanitary condition of onion plantations in the Odesa region are further developed. The results of the research can serve to develop recommendations for production on the implementation of measures to protect onions from stemphiliosis.