1 December 1995

Less volume but more bite in blackgrass war

CEREAL growers can benefit from more rapid knock-down of blackgrass by reducing spray volumes, without cutting rates of chemical, and using finer sprays.

This has emerged from a Ciba Agriculture trial in which the performance of Topik was assessed when applied through a range of systems at varying volumes. The aim was to optimise the herbicides field performance.

"It is likely that the quicker knock-out punch provided by the lower volume fine sprays is because of higher chemical concentration, and better plant retention," said Cibas applications specialist, Tom Robinson.

A fluorescant marker added to the tank showed more chemical reached the weed leaf when a fine spray was applied at 70 litres/ha than at higher 100-, 200- or 400-litre volumes.

Cereal growers may be tempted to apply coarse droplet sprays, as this minimises the drift risk and allows spraying to be done on windier days, so widening the application window.

"But because of poor retention this approach compromises efficiency. We are very wary about the use of coarse droplets as this undermines the potential offered by the chemical," Mr Robinson said.

The Airtec nozzle used in the trial is believed to produce less drift than a standard flat fan.

Long Ashton Research Stations Eric Hislop believes he may have found a workable compromise to provide cereal growers with the best of both worlds. Use of the new Turbo Teejet allows low volume applications of coarse sprays to be applied.

Reduced spray volumes

"So farmers have the advantages of increased output provided by reduced spray volumes without the drift risk associated with fine sprays," he said.

"But as droplet size increases retention on the target plant declines due to bounce. Use of a polymer-based adjuvant stops this, but the droplets may need help to spread out over the leaf. This is where an organosilicone adjuvant could be useful. So in future a mixture of the two types may be needed where chemical is applied as a coarse droplet spray."

Adjusting spray volumes can do a lot to help improve blackgrass control, said Cibas Tom Robinson.