Field investigation of topsoil moisture and temperature as drivers for decomposition or germination of sclerotia (Sclerotinia sclerotiorum) under winter-killed cover crops

ABSTRACT Cover cropping provides versatile benefits for sustainable agriculture, but many cover crops are potential host plants for pathogens such as Sclerotinia sclerotiorum (Lib.) de Bary. Therefore, 14 cover crops were investigated for their interaction with sclerotia, topsoil moisture and temperature in two consecutive field trials in East Austria. In July, after the cover crops were sown, sclerotia were inoculated at 3 cm soil depth in two mesh tubes per plot with 1×1 mm and 3×10 mm mesh size and remained until March. Cover crops did not affect decay of sclerotia, but sclerotia declined faster in 3×10 mm mesh compared to 1×1 mm (75.7 and 54.7%; respectively). Degree days reached the required 500 °C for apothecia development in September in both years, but only in year 1 was topsoil moisture sufficient for apothecia development. Nonmetric dimensional scaling revealed that, among others, topsoil temperature in March was significant for sclerotia germination in spring and was independent of plant biomass. There are indications that Poaceae such as sorghum × Sudan grass and Sudan grass can stimulate early germination under cover crops, causing vulnerability of sclerotia to degradation. This could reduce the pathogen pressure for the subsequent irrigated cash crops.