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Farmers warned of rapid increase in crop-devouring beetle pests

PUBLISHED: 09:41 23 September 2020 | UPDATED: 10:08 23 September 2020

Cabbage stem flea beetles can do significant damage to the oilseed rape crops they feed on. Picture: Syngenta

Cabbage stem flea beetles can do significant damage to the oilseed rape crops they feed on. Picture: Syngenta

Syngenta

East Anglia’s oilseed rape growers are being warned of a significant leap in pest activity which could damage emerging crops.

Sheep grazing established oilseed rape plants at Chris Eglington's farm near Shipdham, in a bid to reduce cabbage stem flea beetle larvae. Picture: SyngentaSheep grazing established oilseed rape plants at Chris Eglington's farm near Shipdham, in a bid to reduce cabbage stem flea beetle larvae. Picture: Syngenta

A rapid increase in cabbage stem flea beetle (CSFB) populations has been recorded at a Norfolk trials site in recent days – which could be a major problem for farmers taking advantage of warm soils and good growing conditions to plant extra areas of oilseed rape (OSR), or with later-emerging plants.

The iOSR Focus Site on Chris Eglington’s farm at Shipdham, near Dereham, is being monitored by agrochemical and seed company Syngenta.

Technical manager Dr Max Newbert said early-sown crops are now well established and have mostly grown away from initial beetle feeding damage. But where there has been protracted emergence in dry weather or new-sown seedlings now emerging, plants at the one-leaf to three-leaf stage are especially susceptible to attack, he warned.

He said the trials had shown well-timed insecticide treatments can still have a significant effect in protecting crops – with plots assessed on September 17 showing a 50pc pest reduction from a single application, and 62pc reduction with two applications.

“The initial treatment was applied just as beetle activity started to take off on the emerged crop, 10 days after drilling,” he said. “Monitoring showed beetle numbers doubled in three days within the trial field.”

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The repeat application, in the first week of September, coincided in a second wave of beetle numbers, which have multiplied three-fold in the past week alone, he said.

The iOSR trials will continue to assess the impacts on future beetle larvae numbers and the effects on final yield.

“The successful early establishment has now seen a surge in renewed interest among growers to plant more oilseed rape, for its value as a break crop in the arable rotation,” added Dr Newbert. “For many it’s a relatively low cost option to see what can be established, with the chance to revert back to a later drilled cereal if the oilseed rape fails.”

The trials site is also assessing other control techniques including sowing OSR with a cover crop of buckwheat and berseem clover, physical beetle deterrents, and a grazing trial using sheep to defoliate well-established OSR plants in a bid to reduce CSFB larvae numbers.


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