Weather dependence of grey rot occurrence in winter rapeseed and brown mustard sowings in the steppe zone of the Western Ciscaucasia

Grey rot, or botritis disease, is a harmful disease of many agricultural crops, the most common pathogen being Botrytis cinerea Pers. (teleomorphic stage of Botryotinia fuckeliana (de Bary) Whetzel). Infection of plants with B. cinerea under conditions favorable to the development of the disease (high humidity of sowings due to high rainfall or heavy dew combined with average air temperatures of 10–25 °C) can lead to yield losses of up to 100%. The aim of the research was to study the influence of weather conditions on grey rot infestation of winter rapeseed and brown mustard sowings in the steppe zone of the Western Ciscaucasia. Studies were conducted in breeding and seed nurseries of winter rapeseed and brown mustard at V.S. Pustovoit All-Russian Research Institute of Oil Crops in 2010–2020. Pathogen extraction into pure culture from diseased plant tissues was carried out under laboratory conditions according to generally accepted methods. During the survey of winter rape-seed and brown mustard sowing, HTC (hydrothermal coefficient) and relative air humidity were taken into account. The relationship between the spreading, HTC and relative air humidity was determined by simple correlation. A strong correlation was found between the grey rot spreading on winter rapeseed and brown mustard and the HTC and relative air humidity in the mid-June. This correlation is positive (direct) and has a linear character. Signs of plant infestation of the studied sowings were observed in years with HTC = 1.1–2.7 (optimal and excessive humidity of environment) in combination with high relative air humidity (63–77 %). An additional factor contributing to the spreading and development of B. cinerea on winter rapeseed and brown mustard was the large number of stem cracks that occurred during the repeated alternation of positive daytime and negative nighttime temperatures in mid and late March.