Spatial distribution of cabbage root maggot (Delia radicum) and clubroot (Plasmodiophora brassicae) in winter oilseed rape crops in the Czech Republic

Abstract

The amount and spatial distribution of plants afflicted with cabbage root maggot (Delia radicum; CRM) and clubroot (Plasmodiophora brassicae) in winter oilseed rape crops were assessed in the Olomouc region (Northern Moravia, Czech Republic) over the course of 2012–2014. A total of 16 commercial rape fields were included in the assessments. Plants with tumours showed a significantly lower (P < 0.001) level of infestation induced by CRM (24% of plants infested) compared to plants without tumours (37% of plants infested). According to a generalised linear mixed model, plants with thicker hypocotyls are predisposed to significantly higher levels (P < 0.001) of root surface damage induced by CRM. The correlation analysis indicates rather weak or intermediate levels of correlation between the two variables (hypocotyls thickness × root surface damage induced by CRM). Both CRM and clubroot symptomatic plants showed a significant tendency for aggregation in rape crops, but not in all cases. Distributions of CRM and clubroot symptomatic plants were either significantly spatially dissociated or not associated in crops. Ovipositing D. radicum females showed some tendency to avoid zones with higher number of plants infected by P. brassicae. Distributions of CRM and hypocotyl thickness levels were significantly spatially associated in crops in several cases.