4 April 1997

Long-term control of

wheat pest…

By Robert Harris

LONG-LASTING wheat bulb fly control is claimed for a new seed dressing expected to be available next autumn.

The product, proposed name Evict, contains tefluthrin, a soil-acting pyrethroid already sold to beet and vegetable growers as Force.

Maker Zeneca says the dressing will be available on both winter and spring cereals, including spring barley, which has no approved dressing at present.

In 30 company trials over the past eight years, tefluthrin boosted average yield by 1.8t/ha (0.72t/acre) compared with untreated plots, says technical manager Mark Hodson.

This season, Zenecas trial site at Ramsey, Cambs, provided a stiff test with wheat bulb fly egg numbers reaching 6.8m/ha. Of those, 99% hatched, most in the last two weeks of January, he explains. The high organic matter soil allowed larvae to move freely, and crops struggled to outgrow damage on the dry site, he says.

Plots treated with tefluthrin drilled on Nov 22 to mimic wheat after roots (the site followed onions) had 55 healthy plants/m row, compared with 38 for fonofos and 23 on untreated plots, Mr Hodson explains. Those treated with egg hatch and deadheart sprays only were similar to untreated plots.

"It is perhaps a little unfair to include the egg hatch sprays since these went on 2-3 weeks late due to the windy conditions – although farmers were faced with the same problem," says Mr Hodson. Plots drilled on Jan 21 to imitate early-sown spring crops produced similar results.

Despite the extreme pest pressure at the site, no benefit was seen by overspraying Blex (pirimiphos-methyl) on the tefluthrin treated plots. "We might have picked up more had the spray timing been better."

The product remains active for several months after drilling, says Mr Hodson.

Activity is independent of soil moisture, aiding persistence, he stresses. In most seasons, there should be no need to monitor and control the pest in spring. But with heavy infestations, a spray may be needed.

The water-based formulation is compatible with a wide range of seed dressings, he adds. It presents a low risk to birds, mammals and soil organisms, and is non-systemic so is safe to the crop and eliminates risk of grain residues.

Application rate is 2 litres/t. A 200kg/ha seed rate equates to just 40g/ha, under a fifth of the fonofos rate, says Mr Hodson. He predicts tefluthrin will command a "small price premium" over fonofos, which it will replace, giving an 80-90% market share.

Severe wheat bulb fly pressure at Ramsey, Cambs, shows the value of tefluthrin seed treatment, pictured here to the right of Zenecas Geoff Hall. Deadheart symptoms (inset left) and wheat bulb fly larvae (inset right) are easily found in the untreated areas of the trial.


&#8226 Proposed name – Evict.

&#8226 Active ingredient – tefluthrin.

&#8226 Controlled release vapour action.

&#8226 Several months activity.

&#8226 Controls wireworms too.

&#8226 Low application rate – 40g/ha.

&#8226 Small price premium over fonofos.