Growers in high risk areas of Aberdeenshire’s River Ugie Voluntary Initiative catchment area are likely to be advised to stop spraying the weed killer isoproturon next autumn.

The broad spectrum herbicide exceeded the 0.1 parts per billion maximum level in final drinking water on 26 days last autumn compared with 12 days in 2004, according to Richard Allan of Robertson Crop Services.

In addition, other herbicides, such as CMPP and triclopyr were also detected in the river water.

“It could be partly because a drier start to the season allowed more area to be cropped,” said Mr Allan, who is the Crop Protection Association representative on the catchment’s VI steering group.

The higher levels of detection were disappointing, he admitted to Farmers Weekly.

“It is everyone’s interests to reduce contamination because of the cost involved in cleaning the water.”

Currently there was no existing plant for extracting pesticides from the drinking water at the extraction point just north of Peterhead, he said.

“It would cost Scottish Water £8m in capital expenditure, and £300,000 annual running costs to clean it up for just 35,000 people.”

Evidence from analysis of contamination of 12 field drains suggested targeted advice in high risk situations could be successful in reducing contamination.

“It is obvious from the results it is where you use it that matters.”

Each of the 12 drains tested were categorised as high, moderate or low risk for their potential to cause problems with drinking water using a surface water vulnerability map produced by the National Soil Resources Unit at Cranfield University.

The testing indicated there was a good correlation between the map and the risk assigned, Mr Allan said.

As a result new advice is being proposed.

“We’ve produced a decision tree for growers and advisers to use.”

For growers on high risk soils the advice would be not to use IPU at all, he said.

“We will be advising alternative herbicides, and if the soil is saturated, growers should not be spraying anything at all.”

On medium risk soils growers will be allowed, when conditions are right, to spray up to 1000g/ha of IPU between 1 April and 31 October, while up to 1500g/ha can be sprayed on low risk soils between 15 March and 31 October.

England’s pilot catchment areas have had a much better year than 2004, VI manager Patrick Goldsworthy noted.

“It’s been a very good year but it has been an exceedingly dry autumn.

The only concern is we’ve put tough new measures in, which we cannot be totally sure whether they have worked, or it is simply down to the dry autumn.”

mike.abram@rbi.co.uk