24 April 1999


With sprayers working flat out, there is a greater risk of spraying a contaminated mixture. We report on advice to avoid setting crops back.

DONT compromise on sprayer hygiene just to save a few pounds this year – you risk losing much more in crop damage.

In the longer term, poor sprayer hygiene with regular clean-ups could cost money in early failures of equipment through lack of maintenance or excessive contamination.

"Whatever chemistry you use, good sprayer hygiene is essential for keeping a sprayer in order, prolonging the life of the sprayer and avoiding damage to sensitive crops," says Martyn Rogers, of DuPont.

He warns against inadequate washing out only with water if herbicides such as sulfonylureas have previously been applied with a sprayer. The penalties for getting it wrong can vary dramatically. Even low tank residues of a sulfonylurea applied inadvertently to field beans will stunt plant growth significantly and lead to yield losses.

DuPont has now added an additional test to its checks after a propiconazole mixture was found to bind to sulfonylurea particles. It became so sticky the residue clung to the inside of a sprayer tank until it was released by another aggressive herbicide being added to the tank by an unsuspecting grower who used the spray on sensitive sugar beet.

DuPont agronomist Andy Selley believes there is a risk of farmers becoming complacent and thinking they can save a few pennies by not using specialist clean-out chemicals such as the ammonia-based All Clear Extra.

Around 10 litres of product are typically left in a sprayer once it has completed its rounds of a field. The least amount is in the sprayer tank itself but 42% of the residue will be found in the sprayer pump and a similar amount in the booms.

Mr Rogers says many operators often forget to clean out the filter when the rest of the sprayer is cleaned out. Drainage of the sump in some tanks is frequently overlooked with expensive repercussions on the next crop sprayed.

Although the new Groundwater Regulations overlooked the fact that sprayer operators use tank cleaners as well as water, the Environment Agency has given the go-ahead for cleaners such as All-Clear Extra to be discharged back to the crop in the same way as washings using water alone.

Its not just the inside of the tank and the booms that need decontamination – the outside of the sprayer needs a clean too. Spray deposits can build up on external surfaces at more than 1% of the volume sprayed per hour, says Bill Taylor, research co-ordinator for Hardi International. And its not just the rear of the tank that will be contaminated – all surfaces can be covered.

The field is the treatment zone for which the product has been approved, so its preferable to decontaminate there rather than in a dedicated area, says Mr Taylor. "But its important to avoid local overdosing of the crop. This is the art of sprayer decontamination."

Just three minutes of clean water rinsing will remove 82% of the external deposit. Reserve a third of water in the flushing tank for the outside of the sprayer, he advises. But the pump must be cleaned before external surfaces are tackled, so wash the internal surfaces first, he adds.

See more