Modelling the impact of cabbage stem flea beetle larval feeding on oilseed rape lodging risk

Background: Cabbage stem flea beetle (CSFB, Psylliodes chrysocephala L.) is a major pest of oilseed rape (OSR, Brassica napus L.) in the UK and low availability of effective chemical control has increased the need for integrated pest management approaches. The risk of OSR to lodging is strongly related to stem strength, however, the impact of CSFB larval tunnelling on stem strength and subsequent risk to stem lodging is unknown. The study investigated this by applying the Generalised Crop Lodging Model to conventionally grown OSR crops scored for varying levels of CSFB larval tunnelling. Lodging risk mitigation strategies including plant growth regulators (PGR) and varying nitrogen regimes were tested under high CSFB larval pressure.

Results: Stems of OSR plants were categorised by the proportion of visual damage (< 5%; 5-25%; 26-50%; 51-75%; 75-100%). Stems of 26-50% damage had significantly lower breaking strengths and diameters compared to plants that scored < 5%, with the associated reduction in stem failure windspeed equivalent to an order of magnitude increase in the risk of a lodging event occurring in the UK. PGR use reduced plant height and subsequently lodging risk variably across the sites.

Conclusion: Estimating the proportion of stem tunnelling alongside larval pressure may be a useful tool in considering the contribution of CSFB pressure to lodging risk. The research demonstrates that the use of canopy management principles to optimise canopy size through nitrogen management and PGR use may help offset increased lodging risk caused by CSFB tunnelling. © 2024 Society of Chemical Industry.