Weather stations aid pesticide use

24 January 1997

Future role for novel fungicides

The annual conference of the Association of Independent Crop Consultants spawned some thought-provoking discussions, not least on the role of novel fungicides. Andrew Blake reports

EVEN with the arrival of the new family of strobilurin fungicides, it should make sense to stick to basic fungicide principles, an ADAS pathologist told delegates.

"We have to ask what are we trying to do with timings," said Dr Neil Paveley. One discussion group felt that striving to protect more than the top three leaves in wheat was usually uneconomic.

Comparing contributions from various parts of plants in thin and thick crops Dr Paveley noted that relatively more yield came from ears and flag leaves in the latter. "So at high nitrogens if you keep the ear and three leaves clean, you are probably covering everything."

Diana Nettleton from the Cotswolds was intrigued to see how much ears contributed. But Dr Paveley warned that specific ear sprays were rarely beneficial. Sooty moulds usually came in when the ear had stopped adding to output, he explained. "Mildew on the ear is usually a sign that the programme has gone wrong earlier."

Henry Overman from Kent, convinced that chlorothalonil made spray programmes more robust, highlighted the practical problem of maintaining disease defences in catchy weather. "We must stay ahead of the game if we have big acreages."

Dr Paveley conceded the need for flexibility. "I agree – we cant be totally precise." He used research results to show that the key to control, irrespective of the type of fungicide, was to ensure correct timing, so gaps in protection were minimised.

For any given disease and fungicide there was an optimum timing, control falling away the further one deviated and used reduced doses. Analysis of results shows the best control coincides with the full rate at the best timing according to the leaf involved – for example for Septoria tritici, about 7-10 days after leaf emergence.

The key is knowing how control varies either side of the optimum, he said. By comparing numerous trials results it is possible to gauge the potential effectiveness of any given strategy.

The effect of the latest fungicides was to extend optimum control, giving growers more timing leeway, he explained. He felt researchers now had a shrewd idea of how far that extra control extended.

Knowing when an application ceased giving control would be a big help, said Mr Overman. "The difficulty is knowing when we are running out of cover." Consultants needed to be able to cost the consequences of not re-spraying apparently clean crops with latent disease, he added.

Applying sound principles should help offset misguided perceptions of unnecessary insurance treatments, suggested Dr Paveley.

New fungicides for cereals wont eliminate the need for careful timing, AICC delegates heard.

Linseed usage catches herbicides on the hop

TREAD warily with herbicides for winter linseed. That was one consensus after an AICC/Semundo discussion.

Expansion of the crop from virtually nothing two years ago to perhaps 30,000ha (74,000 acres) this season seems to have caught manufacturers by surprise.

"The crop has jumped ahead of agrochemical companies," said Semundos Fiona Davies. Trifluralin in particular came under the spotlight, especially manufacturer advice to incorporate it.

Last year about a third of Semundos 200 growers used the herbicide with pre-emergence treatments generally giving good results, said Mrs Davies. But some crops on light land suffered.

Reduced vigour and lower plant populations from trifluralin treatment of spring linseed had steered Hants-based Richard Cartwright away from the herbicide for the four winter crops of Oliver under his care last season. Falcon (propaquizafop) followed by Ally (metsulfuron-methyl) was his main line of attack.

This season Bryce Rham from Shropshire used incorporated trifluralin on winter crops on heavy land as advised by DowElanco. "So far we have seen no damage, but it is an area for confusion."

Urging caution Mrs Davies agreed there was a need for more work on the subject. "We say spray the day after drilling but do not incorporate. Our two growers who did certainly got damage."

Weather stations aid pesticide use

IN-FIELD weather stations radio-linked to farm offices to guide field operations and optimise pesticide use are fast becoming part of the Danish farming scene, according to Margrethe Hostgaard of Hardi.

The country failed to meet its target of cutting pesticide use by 50% by the end of last year, she told AICC delegates. So now agrochemical taxes have been imposed to fund research into better forecasting scheme to help growers.

Key to such systems is accurate weather data collection which growers can get through the companys 12-sensor Metpole, Miss Hostgaard explained. Four years after its introduction there are said to be about 150 on Danish farms.

Trials in Ireland and Denmark using the Negfry potato blight prediction computer program accompanying the Metpole have proved encouraging, she said. "It has been able to predict disease before it breaks out, and in some years growers have been able to postpone first treatment by five weeks.

"Until recently farmers were quite wary. But 1995 turned around their whole perception." It was the first time the program had advised a first spray before June 20. Growers following it went on three days early and were the only ones who kept on top of the disease, she claimed.

Other models for predicting cereal and onion diseases are on the horizon.

Miss Hostgaard said better use of field weather stations was politically useful. "It is helping to convince politicians not to set a maximum number of sprays."n

An increasingly common sight on Danish farms, the Metpole helps make best use of pesticides.

&#8226 Timing and rate still key, even with new fungicides.

&#8226 Protecting ear and first three leaves main goal.

&#8226 Aim is to identify how much new products boost flexibility.

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