17 July 1998

Adjuvant oils dont mix with air-type nozzles

By Mike Williams

BE careful when using air induction type nozzles with adjuvant oils, warns a crop protection specialist company.

A lack of compatibility between adjuvant oils and pre-orifice nozzles became apparent in trials carried out by Cambs crop protection specialists, Hutchinsons.

"Although air induction – or pre-orifice – nozzles may reduce drift when adjuvants are added, droplet size may be altered," says Dick Neale, Hutchinsons technical manager.

The company used a sprayer fitted with Lurmark Driftbeta nozzles to apply herbicides with an oil-based adjuvant in blackgrass control trials this season. According to Mr Neale, it was obvious the nozzles were not working properly.

"This type of nozzle works by modifying the spray droplets," he explains. "Using an oil based adjuvant in the mix appears to interfere with the droplet structure – possibly because it breaks up the surface tension which forms the droplets."

Mr Neale says it was easy to see that the spray pattern was seriously affected and, as a result, showed up in the trial plots.

"When we replaced the Driftbeta nozzles with standard flat fan nozzles to spray the herbicide and adjuvant oil, the sprayer worked normally. We also tried flushing the spray mix and adjuvant oil out of the sprayer and then sprayed the same herbicide without oil through the Driftbeta nozzles – and that also worked well," he says.

Mr Neale points out that air induction nozzles of the Driftbeta type can achieve excellent results in drift reduction, and concedes that they may work well with adjuvants which are not oil based. "But they do not work with oil," he insists.

A spokesman for Lurmark said Driftabeta nozzles are widely used. The company was not aware of any problem occurring when the spray mix contains adjuvant oil.