Maintaining the armoury against WBF

04/02/12

With a key component of the Wheat Bulb fly control armoury under threat, abiding by new application requirements for imminent chlorpyrifos applications will be a number one priority in the hotspot region of the Cambridgeshire fens.

According to AICC agronomist Mike Thompson, chlorpyrifos insecticides are so important to Wheat Bulb fly control, that without them, he believes the very viability of wheat in many rotations would be brought into question.

“Irrespective of the official egg count data, there are areas where the pest will always be a problem, year on year,” he says. “It’s an endemic issue for wheat crops where the previous row crops such as sugar beet and potatoes allow an entry point for adults to lay eggs during August and September,” he explains.

 “And with many fields in the arable dominated region being adjacent to dykes or streams, growers will feel the full brunt of the new requirements of the chlorpyrifos,’ Say No to Drift’ initiative,” adds Mike. Introducing the necessity to apply the insecticide using three-star rated low drift nozzles, the guidelines – launched in December by the three UK approval holders of chlorpyrifos products – also demand an increased 20 metre buffer zone.

Yet, they are measures well worth taking in the drive to keep chlorpyrifos on the market, believes Mike. “During bad years for the pest, and in high egg count scenarios, we depend on chlorpyrifos as the only means of controlling the hatched larvae. Each larva is capable of destroying three tillers each, so at 250 eggs per m² in high risk situations, a crop – averaging just 200 plants per m² – could be decimated.

Falling foul of that very scenario, Mike Mottram – an arable producer based in March, on the Cambridgeshire fens – ran short of chlorpyrifos product for 6 acres of a 49 acre field in 2011. He describes the season as the worst for Wheat Bulb fly that they have experienced and believes that around 200 acres were saved from re-drilling as a result of chlorpyrifos use. The untreated section of the fields was testimony to its efficacy.

“The six acres was entirely wiped out,” says Mike Mottram. There was a defined line between the treated and untreated area of the field and it entailed re-drilling lower yielding spring wheat. With seed costs alone at £400/t, as well as the extra labour, fuel and inconvenience, it really showed the value of the insecticide.

Mike Thompson goes on to explain that whilst seed dressings provide a useful defence, they can run out of steam where drilling timing combined with weather conditions conspire to increase vulnerability to pest attack. Although in his experience, he says that chlorpyrifos is a very necessary addition to a seed treatment in a high risk year.

Despite the high level infestations in 2011, latest reports from the ADAS egg count data for Wheat Bulb fly show 2012 levels are lower than average. Egg hatch survey results are now imminent and will inform timings for chlorpyrifos treatments.

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