23 November 2001

Patch spraying waits to take off commercially

PATCH spraying is set to become a commercial reality, with Rau launching its first camera-controlled system at the Agritechnica machinery show in Germany and scientists detailing cost savings at the British Crop Protection Conference in Brighton, last week.

The Rau system uses a digital camera to sense weed patches, said Roland Gerhards, of the Plant Science Institute in Bonn. Sophisticated computer technology then identifies the species involved acc-ording to its leaf outline.

German growers will be able to hire in a contractor to patch map weeds in sugar beet, maize and possibly cereals for just £6/ha next spring. Digital maps will then be created to adjust spray applications accordingly.

Patch spraying field trials cut herbicide use by 11-92% and costs by £16-£26/ha. Significantly, some areas received no herbicide throughout the four-year study, offering environmental benefits, added Mr Gerhards.

Work is now looking at the use of a camera mounted at the front of the sprayer to provide live weed data to adjust rates during spraying.

Assessing disease in the same way also shows promise. "We have been able to identify and quantify diseases in real time," said Mr Gerhards.

Meanwhile, work at IACR Rothamsted shows patch spraying can cut herbicide use by up to 42% and save between £2/ha and £18/ha. That more than covers the £1.38/ha labour cost of mapping weeds from an ATV before spraying.

Mapping equipment may cost £7000, but can be offset against other operations, said IACR Rothamsteds Nicola Perry. Variable rate spray controllers cost between £2000 and £6000.

By mapping before spraying better decisions can be taken about product choice, environmental protection, tank mixing and the amount of spray needed, so avoiding wasteful leftover, said Helen Wheeler, of Silsoe Research Institute.

Buffer zones can also be created around patches to prevent spread. Field trials over a number of years show a 4m buffer contains wild oat patches effectively. &#42