How to use oilseed rape sowing dates to reduce CSFB risks

Sowing oilseed rape early or late (compared to traditional dates) can have a big impact on cabbage stem flea beetle (CSFB) adult and larval pressures. Siobhan Hillman explains how this can be exploited in management strategies.

Last year, we published a list of the top CSFB management strategies.

One of the most important states ‘ditch the date’ and provides the following specifics:

• Avoid the traditional end-of-August/early-September sowing dates, as this is when peak CSFB migration usually occurs (typically, late-August to mid-September)
• Sow early (early- to mid-August) to maximise tolerance to adult feeding
• Sow late (mid-September onwards), after migration has peaked, to minimise adult damage and reduce larval load

This month, we published a new web page that explores the evidence that underpins the above points.

Meticulous monitoring work over several years, mainly at oilseed rape sites in England, has given us a good understanding of the broad trends for both CSFB adult and larval activity.

When it comes to CSFB adults, the trick is to avoid peak beetle migration coinciding with crop emergence (either by sowing earlier or later).

For larvae, it is important to consider the longer egg-laying period and potentially greater egg-laying rate (because of warmer conditions) in early-sown crops.

This is why early sown crops are associated with greater larval infestation later in the autumn and into the spring.

As a result, drilling dates need to consider both risks: adults and larvae.

Although migration patterns are broadly similar across the country, timings fluctuate across seasons and locations.

Once again, we will publish regular updates on the number of CSFB adults, caught in a network of yellow water traps, to indicate this year’s migration trends (starting in August).

Currently, we are gathering this data as part of CSFB Research+.

For on-farm decisions, monitoring data is particularly useful to guide drilling dates after migration has peaked.

Finally, there is one other important variable to consider: soil moisture.

As dry conditions can slow establishment, it is critical to wait for moisture (present or forecast) before sowing crops, especially when drilled before peak migration.

This article and new web page are the first in a series that will examine the evidence behind each management strategy.

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

Use integrated pest management (IPM) to layer as many techniques as possible to minimise the risks.