### The role of reproducible research tools in quantifying a decade-long survey of Sclerotinia disease prevalence, in South Africa. ---------- ##### Rothmann, L.A. (1), McLaren, N.W. (1) and del Ponte E.M. (2) ##### (1) University of the Free State, Department of Plant Sciences, Plant Pathology. ##### (2) Federal University of Viçosa, Phytopathology Department, Epidemiology. ---------- _Sclerotinia sclerotiorum_ is a polyphagous fungal pathogen that occurs globally and causes diseases locally known as Sclerotinia stem and head rot of soybean and sunflower, respectively. Oilseed crops contribute significantly to the area planted across South Africa and are considered economically important. This study aimed at summarising, through the use of reproducible research tools, the Sclerotinia disease intensity across soybean and sunflower production regions in South Africa based on a survey with data collected over a 10-year period (N = 1331). Sclerotinia disease intensity was assigned as a percentage of the farmer's perceived field area affected by Sclerotinia, as well as either healthy (0) or diseased (1) enabling the calculation of Sclerotinia disease prevalence. Disease intensity as well as prevalence were mapped. The extent to which the survey was representative of the population was determined and mapped. The responses reflected prominent production regions; Free State, KwaZulu Natal and Mpumalanga and the Free State and North West provinces for soybean and sunflower production, respectively. The survey represented between 1.3 and 16.7% of the area planted to soybean, while sunflower representation ranged between 0.4 to 94.3%. The lowest prevalence of 15.2 and 3.2% was recorded in 2015 (n=112) and 2013 (n=95) for soybean and sunflower, respectively. The North West (n=57) and Limpopo (n=49) had the lowest mean prevalence, of 7 and 10.2%, for the duration of the survey in soybean and sunflower, respectively. Whereas, the highest mean Sclerotinia disease prevalence of soybean and sunflower, of 55.7% and 100%, was reported in Mpumalanga (n=244) and the Northern Province (n=3). The association between mean January, February and March weather parameters and Sclerotinia disease was investigated, through correlation analysis, to determine parameters potentially responsible for variation observed. A negative association between Sclerotinia disease and maximum and minimum temperature, as well as a positive association between precipitation and relative humidity was reported. The relationship between the previous crop planted and Sclerotinia disease intensity was explored through a conducting a Mann-Whitney U test (n = 379). There was no significant reduction in Sclerotinia disease where maize was planted in the previous year. The sporadic nature of this pathogen, the current epidemics observed across South Africa, and potential spread to canola in the Western Cape further underpin the urgency required to understand the underlying processes driving epidemic development. ##### **Keywords**: _Sclerotinia sclerotiorum_; national survey; epidemiology; disease distribution; temporal distribution; rotation