28 August 1998

IPUs…more care is

needed now


herbicide use to

give optimum

weed control at

least cost is the

goal this autumn.

That is the same



meadow-grass or


weeds are your

main concern. In

this special

extended feature

we examine

the latest advice

for getting the

most from

herbicides this

autumn. Edited by

Charles Abel

ISOPROTURON residues in drinking water supplies reached record levels in some regions last winter. If growers want to keep ipu products in their herbicide armoury they must use them more carefully this autumn.

That is the blunt message from the water industry as it shoulders clean-up costs running into millions of pounds. Over the past three years companies have spent over £400m to remove pesticides from water, with IPU the main target.

Hardest hit has been Thames Water. "Residue levels were absolutely diabolical last winter," says Reading-based senior scientist Dinah Hillier.

"At Walton on Thames, for example, we had to run equipment for 113 consecutive days to bring ipu levels below the 0.1 parts per billion limit required by the EUs drinking water directive. That compares with just 46 days in the dry 1996/7 season and only 82 days in 1995/6, the previous worst season.

The agrochemicals industry has been concentrating on point source spills and washings too much, she believes. "Peaks early in the season may fit industry claims that spills and sprayer washings play a role. But elevated levels persisted right through the winter, pointing to a greater role for normal field applications."

Blaming industrial use of ipu is also dismissed. "Weve looked at industrial users, like the railway companies, and they are not using ipu."

She believes agriculture needs to do more. "Last winters results show the industrys stewardship programme is not making the inroads we believed it was previously."

That position is acknowledged within the farming industry. "The data is clearly worrying, but it would be wrong to say point source is not significant," says Jim Orson, director of Morley Research Centre in Norfolk and a member of the industrys ipu task force.

"Data from Germany suggests up to 80% of the problem there is point source."

But there is still much to do on stewardship, he adds. "At Morley we will be launching an initiative to minimise point source problems this autumn."

IPU application should take account of soil conditions too, he says. "Its efficacy is very reliant on weather conditions. It does need some rain within one or two weeks after application, but exceptional levels of rain can move it just below the critical top 4mm of soil, where it must be for effective control."

Preparing a fine tilth and avoiding applications to dry soils will help reduce run-off and improve weed control, he says.

Mr Orson also urges growers to look at reducing rates, especially where alternatives can be used as mixture partners. "But dont mix ipu with flupyrsulfuron, as in Lexus. Its a great shame, but the two are antagonistic, leading to poorer control."

Steve Higginbotham of Rhone-Poulenc and chairman of the industrys ipu task force echoes his views. "Last year was a tricky season and we are still learning a lot, especially about point source. New evidence suggests residues which build up on the sprayer can have a significant role."

That makes regular sprayer wash-down important, to prevent contamination risks if rain washes residues near a drain. "Washing the sprayer regularly and in the field will help cut the risk of ipu contamination," says Mr Higginbotham.

He also urges growers to follow the guidelines laid out in the task forces IPU Stewardship programme. "It is very much in the farmers hands. They need to be aware of the problem and to do something about it.

"We will be working more closely with the NFU in the highest risk areas, like the Thames Valley which takes most of its water from surface supplies." Meetings, catchment studies and information campaigns are planned.

A key message for growers is the significant damage even minute amounts of ipu can cause, Mr Higginbotham stresses. "The EU limit is equivalent to half a second in 70 years or 4mm out of the circumference of the world. Growers need to be aware that only very small amounts of ipu can cause a lot of damage."

He also points out that the 0.1ppb limit stems from EU legislation and is not based on proven health or environmental safety risks.


&#8226 Use it properly, or lose it.

&#8226 Have a plan to deal with spills – use sand to absorb and dispose of safely. Do NOT rinse away.

&#8226 Avoid leftover spray – match last load to area of field left.

&#8226 Clean sprayer and protective clothing regularly, in safe area.

&#8226 Use cultivations which minimise run-off – eg contour ploughing.

&#8226 Avoid spraying dry soils – wait for damp soils for best results and least leaching risk.

&#8226 Aim for a fine soil tilth.

&#8226 Avoid drift near water.

Alternative on market…

AS pressure on isoproturon intensifies, the arrival of a flupyrsulfuron-only formulation of Lexus this autumn looks timely indeed.

Lexus 50DF contains residual and contact acting herbicide flupyrsulfuron, as in Lexus Class, without carfentrazone-ethyl. The 50% dry flowable formulation controls grasses and broad-leaved weeds in winter wheat.

"At 20g/ha its low rate of active ingredient means a good environmental profile and the opportunity to replace ipu in autumn winter wheat programmes," explains Martyn Rogers, herbicide product manager for Du Pont. "It gives more consistent control of blackgrass than IPU and control of difficult broad-leaved weeds such as cranesbill, groundsel and shepherds needle.

"When applied early at the 1-2 leaf stage of blackgrass we would expect 90% or better control from Lexus alone.

Tank mixing can take that nearer 98%. For resistant blackgrass we would recommend the use of Avadex pre-emergence followed by Lexus plus Treflan or Stomp within four weeks, or before three leaves of the blackgrass. Tank mixes with Hawk offer an alternative strategy for the control of target site and metabolic resistant blackgrass."

Lexus 50 DF will be available this autumn in a 4ha (10 acre) 80g jar. Du Pont claims it will be competitively priced against 5l/ha ipu. There are no restrictions on follow-on use of other Du Pont sulfonylureas, the company adds.

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