Flea beetle research results

A 68% reduction in adult beetles coming out of the ground in September to feed on newly emerging crops has been recorded where cultivation took place immediately after harvest, reports Colin Peters of Niab.

Work to understand more about the most effective form of cultivation has stalled, following the loss of funding, but early indications suggested that the best results came when the top profile was thoroughly stirred, he adds.

“We also looked at companion crops and we did see differences in larvae numbers, but that work now needs doing on a larger scale.”

Otherwise, there is increasing anecdotal evidence that growing oilseed rape away from the previous years crop will reduce emergence damage.

“The suggested distance is 2km, but we haven’t tested this yet,” notes Colin. “The work has been done in Sweden and initial results suggest it is better than growing oilseed rape adjacent to the previous crop and using volunteers as a trap crop.”

Flea beetle risk reduction pointers

Adults

• Rapid, vigorous and even establishment – soil moisture, nutrition, etc
• Sowing date and seed rate – early to tolerate damage or late to avoid adults
• Companion crops – reduce beetle numbers
• Trap crops – do they attract flea beetle away from cash crop?
• Organic amendments – deter adult beetles?
• Post-harvest cultivations – a method of reducing overall numbers
• Pre-sowing cultivations – anecdotal evidence of lower numbers with min-till
• Stubble/straw management – reduces levels of damage

Larvae

• Sowing date – spread dates, the later the better 
• Companion crops – lower larvae numbers where used
• Trap crops – does leaving volunteers attract the pest?
• Seed rate – higher seed rates result in more larvae
• Defoliation – grazing or topping, beware yield impact
• Pre-sowing cultivations – do they help?

Case studies

Ben Jackson, North Lincolnshire

For North Lincolnshire grower and United oilseeds chairman Ben Jackson, growing oilseed rape for the past 10 years has not been without its difficulties.

Up until 2022, oilseed rape was the second-best paying crop on the farm, average yields were 3.8t/ha and pre-Christmas crop losses didn’t exceed 5%.

As a result, it was 25% of the rotation.

But 2023 and 2024 were very different years with plenty of challenges and the results plummeted, he recalls.

“For harvest 2023, we lost 20% of the crop before winter and our average yield was 2.8t/ha.”

Worse was still to come. In 2024, despite reducing the crop area to 15% of the rotation, as much as half of the oilseed rape area was lost and yields dropped again to 2.5t/ha.

“We encountered a bit of everything,” he says. “Flea beetle pressure, slugs, pigeons and flooding were the main issues – a familiar tale for many growers.”

Despite that, Ben has persevered with the crop and tried various mitigations.

“We’re on heavy land which is not really suitable for spring cropping and there’s no avoiding the fact that oilseed rape is the best paying break crop in most years.”

His loyalty seems to have been rewarded. His harvest 2025 crop – which is 10% of the cropped land – has established well and pre-Christmas losses were back to 5%.

“I’m much more hopeful this year; it looks fantastic.

“We are also de-risking the crop with Sustainable Farming Incentive actions, such as companion cropping and precision fertiliser, as well as a summer cover crop after oilseed rape.

“It will put a base income into the crop and take some of the risk out of it.”

This spring’s survey of stem larvae numbers will also help, believes Ben. “It should give us an idea of what the pressure will look like later in the year and understand what the risk is for the next crop.”  

Julian Gold, Oxfordshire

Oilseed rape is grown on a 1 in 6/7 basis at East Hendred Estate in Oxfordshire, where the five-year yield average is 3.09t/ha.

Farm manager Julian Gold acknowledges that there are risk factors with the crop, but stresses that it holds its own in most years.

Yields have come back a bit, he notes, but the regenerative system in place on the farm means that he is using lower nitrogen rates than he used to.

“I’m going to continue pulling them down from the current level of 190-200kg/ha, so it will be interesting to see what happens with output,” he says.

Establishment is key, believes Julian, who has switched to hybrid varieties at 50 seeds/sq m and will not drill if there is no rain forecast.

Companion crops are a must, as is plenty of consolidation, with rolling done two or three times to guarantee seed-to-soil contact.

Flea beetle has not been a big problem, which Julian attributes to the wide rotation and inclusion of companion crops. Mixing berseem clover in with the rape seed, at 4-5kg/ha, has worked well.

The crop is not grown adjacent to fields that had it previously or where the winter bird food option is in place. “We’ve seen crop damage in these locations before, so we avoid them now.”    

Otherwise, the aim is to keep input use down.

The main spend is on post-emergence Belkar (halauxifen+ picloram) herbicide, an autumn and spring fungicide and good nutrition, including boron and magnesium.

“Growth regulation is usually cost-effective, as are pod stickers.”  

A pod stick product used in a separate pass has allowed him to leave out a pre-harvest glyphosate application. “But you need to remove the cleavers if you want to harvest without glyphosate.”

Poultry manure was used last autumn, so he currently has very lush, forward crops. “Now I’m wondering if they are too thick. I aim for a green area index of 3.5 at flowering.”