CSFB larval populations amongst the highest for 15 years

22.01.2019

Even if you escaped damage from adult cabbage stem flea beetles (csfb) in the autumn, you could still be at risk of csfb larvae decimating crops from within.

In this blog, Dr Sacha White, ADAS entomologist discusses the latest results from a three-year AHDB funded project looking into developing an integrated pest management (IPM) programme for cabbage stem flea beetle (csfb).

“This autumn we have assessed five sites to determine levels of csfb larval infestation as part of our project.  Larval populations are relatively high; with one site having the second highest in 15 years of autumn larval assessments (19 larvae per plant).

Historically, the bulk of csfb egg laying happens in the period from September to October. However, recent mild winters have allowed adults to continue egg laying and eggs to develop, causing big increases in larval populations over winter. The high autumnal larval populations we have found are perhaps to be expected as we had such a warm September/October which has encouraged early egg laying and rapid larval development.

We are in the final year of the three-year AHDB Cereals & Oilseeds funded project and are looking at data from over 1600 sites across England and Scotland, on csfb damage, going back 14 years.

Our modelling of this data has shown that there are factors which are important in determining larval populations in the autumn and the spring.

Autumnal larval populations

Average September temperature

An average September temperature above 15oC was where we started to see high larval populations, when average temperatures were lower so were larval populations.

Spring and early summer rainfall

Relatively high rainfall in spring and early summer resulted in low larval populations in the autumn. At present we are not sure exactly why this happens, anecdotally we know that csfb dislike rain and rainfall may also encourage csfb pathogens earlier in the year, killing adults and larvae as they pupate.

Sowing date

September sowing dates correlated significantly with lower larval populations in both autumn and spring.

If you have an early August drilled crop then the adult flea beetles are likely to be in that crop longer, feeding earlier and egg laying earlier.

However, the key with sowing date is to be flexible and wait for the conditions which will allow establishment of a vigorous healthy crop.

Spring larval populations

Average temperature in November and January

High temperatures in November and January seem to have a very important influence on spring (February, March and April) larval populations, with high temperatures resulting in high larval populations.

Mechanical control?

ADAS are trialling a novel method for csfb larvae control which involves defoliating the crop before stem extension. Preliminary results have shown significant reductions in the larval populations where we mowed in December or January and that yield was not negatively affected by defoliation. Further trials are underway this winter to better understand this control option.”

ADAS, in conjunction with Innovative Farmers, would like to set up a network of farmers interested in trying this approach on their crops.

If you would like to take part or have any questions please contact Dr Sacha White at sacha.white@adas.co.uk.

Click below for previous cabbage stem flea beetle posts:

Risk mitigation strategies: Part 1

Risk mitigation strategies: Part 2

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