Weather dependence of grey rot occurrence in win-ter 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 hu-midity 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 condi-tions 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 Re-search Institute of Oil Crops in 2010–2020. Pathogen extraction into pure culture from diseased plant tis-sues was carried out under laboratory conditions ac-cording to generally accepted methods. During the survey of winter rapeseed and brown mustard sowing, HTC (hydrothermal coefficient) and relative air hu-midity were taken into account. The relationship be-tween the spreading, HTC and relative air humidity was determined by simple correlation. A strong cor-relation 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 ob-served in years with HTC = 1.1–2.7 (optimal and ex-cessive humidity of environment) in combination with high relative air humidity (63–77 %). An addi-tional factor contributing to the spreading and devel-opment of B. cinerea on winter rapeseed and brown mustard was the large number of stem cracks that oc-curred during the repeated alternation of positive day-time and negative nighttime temperatures in mid and late March.