CSFB management tip: Cultivate OSR stubble

Cabbage stem flea beetle (CSFB) management in oilseed rape (OSR) requires a combination of approaches. Find out how cultivating stubble after harvest disrupts soil-dwelling pupae.

Integrated pest management (IPM) targets specific stages in a pest organism’s life cycle.

After gorging on oilseed rape stems, CSFB larvae drop to and pupate in the soil.

As most CSFB pupae reside in the top 30 mm of soil, it makes them vulnerable to tillage operations.

Originally, it was thought that CSFB adults mainly emerged from pupae during the late spring or early summer.

There is now building evidence that many adults emerge later, including after harvest of the standing oilseed rape crop.

Niab-led csfbSMART project trials provided initial evidence of the potential to target pupae after harvest.

The research assessed the impact of various post-harvest cultivations in oilseed rape stubble by comparing them with an uncultivated control.

They used sites with high larvae numbers in the previous oilseed rape crop to promote high levels of CSFB pupae.

They regularly counted the adult beetles caught in emergence traps from harvest to the planting of the following crop.

In 2022, the site treatments included:

• A shallow 50 mm cultivation in East Cambridgeshire
• A 250 mm deep cultivation in West Cambridgeshire

A packer-roller was also used to prepare the seedbeds.

The trials clearly showed that significant numbers of adult CSFBs emerge from the soil during August and September.

This aligns with the typical main CSFB migration period.

Beetle numbers were much lower in the treatments where the soil had been cultivated.

East Cambridgeshire:

• Cultivation reduced CSFB adults caught in traps by over 90%
• Most were caught between the end of August and the middle of September
• The peak day was in early September, with about 800,000 and 200,000 beetles/ha caught in the uncultivated treatment and cultivated treatment, respectively

West Cambridgeshire:

• Cultivation reduced CSFB adults caught in traps by 68%
• Most were caught between the middle of August to the middle of September
• The peak day was in early September, with about 600,000 beetles/ha caught in the uncultivated treatment, with less than 30,000/ha caught in the cultivated treatment

In 2023, similar results were seen at four trial sites: Essex, Hertfordshire and two sites in Shropshire.

Compared to the uncultivated treatment, the number of CSFB adults caught in traps was reduced by:

• 49% to 85% by shallow cultivation
• 69% to 98% by deeper cultivation
• 37.5% to 68% in a straw-rake treatment, at the two sites with this additional treatment

Beneficial organisms, also called natural enemies, can potentially deliver moderate control of CSFB.

For example:

• Some carabid beetle species feed on CSFB eggs and young larvae before they enter OSR
• Tersilochus microgaster and Microctonus brassicae parasitise the larval and adult stages, respectively

As the pupal stages of these species also inhabit soil, they are also vulnerable to cultivation.

We will continue to quantify the impact of post-harvest cultivation at two trial sites for two years in the CSFB Research+ project, which will assess both CSFB adults and beneficial organisms.

Philip Wright, Wright Resolutions Limited, and Colin Peters, Niab, explain how to set up cultivators to move soil sufficiently and consistently in two YouTube videos.

Due to the complex nature of CSFB, never rely on a single strategy.

Use IPM to layer as many techniques as possible to minimise the risks.