Oilseed rape hit by cabbage stem flea beetle larvae

Article taken from the Farmers Guardian, written by Georgina Haigh

High levels of cabbage stem flea beetle (CSFB) larvae are being reported in oilseed rape crops, particularly in Bedfordshire, Cambridgeshire and Hertfordshire, which could result in large numbers of adult beetles in crops this autumn, says agronomists.

The loss of neonicotinoid seed treatments has left very few effective control methods for CSFB, particularly as cases of resistance to pyrethroids are growing.

Hotspot areas

Agrovista technical manager Mark Hemmant has seen large numbers of CSFB larvae in OSR crops around Cambridgeshire and Hertfordshire, which he says are ‘traditional hotspot areas’.

He says: “In companion plant trials, we have seen an average of about 16 larvae per plant, which is about 400 larvae per sq.m.”

The current spray threshold for autumn or early winter is two larvae per plant, but it is debatable whether sprays will be effective now as larvae move into plant stems, becoming harder to target, says agriculture consultancy ADAS.

Mr Hemmant adds:  “Larvae are either in stems or they are going to be shortly – we will not get them [with sprays] now.”

Strutt and Parker farming consultant Edward Hutley, who advises farmers across Bedfordshire, Cambridgeshire, Hertfordshire and Oxfordshire, has also seen larvae in OSR crops.

He says: “There is a fairly high incidence across Cambridgeshire and Bedfordshire, with large populations of adults.  At the moment, larvae are on the leaf and boring towards the stem.  Unfortunately, the only time to control cabbage stem flea beetle is at adult stage.

“I think most people are unsure of the implications but I suspect there will be yield damage, although it is hard to put a figure on it.”

Mr Hemmant adds:  “The problem is nobody can remember having this level of larvae per plant, so we do not know what the damage will be.”

Although both experts agree there are few effective control options left for this season.  Mr Hemmant says he is ‘hopeful’ the impact on this year’s crop will not be as bad as feared.

He says larvae feeding on bigger plants do not seem to have reached the stem, which would enable them to eat flower buds and impact yields before leaving plants and starting the metamorphosis process.


However, large larvae populations this spring will increase the attack on adult CSFB on crops this autumn, says Mr Hemmant.

“Growers need to judge how bad it is now and start making plans because the situation will be worse next year as we have had no control this year.

“Those in hotspot areas are going to have to consider their options and might want to think about not growing oilseed rape,” he says.


27 March 2015

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