UNTIL WEEDS can be identified easily and automatically by remote sensing, variable herbicide sprays are unlikely to become commonplace.

That is despite the huge potential financial savings and advances in sprayer technology, which could allow sprays to be switched on or off almost instantaneously.

“Farmers are very reluctant to produce a weed map,” says The Arable Group”s Jim Orson. “So we need easier and quicker methods of assessing weeds.”

That is a real challenge, he admits. “Pre-emergence applications are essential for grassweeds, because of resistance, and post-emergence sprays tend to go on very small weeds. You cannot underestimate the challenge.”

Grower attitudes to weeds would also have to change for variably applied sprays to take-off, he adds. “They are very unwilling to leave areas of fields unsprayed as they think in the long term it will be a mistake.”

A direct injection system that can switch chemicals on or off within 5m in the field makes variable spraying feasible, notes Knight Farm Machinery’s Brian Knight. “That is much quicker than has been possible.”