23 May 1997

Slow sprays – less drift

SPRAYER operators who drive too fast are more likely to cause drift problems than those who keep their speed down, according to Silsoe Research Institute.

Tests carried out with a boom sprayer – in wind tunnel and field situations – showed that air currents created by forward movement of the sprayer affect the spray droplets after they leave the nozzles.

"If the operator is driving too quickly, the droplets may be deflected from hitting the crop and lost as spray drift," explained Dr Clare Butler-Ellis, speaking at an Institute of Agricultural Engineers conference at Silsoe College.

"Increasing the forward speed of the sprayer in a given wind speed increases the risk of drift," she said. "Results from wind tunnel testing showed that in a wind speed of 10.8kph measured at boom height, increasing the forward speed from 5.4kph to 9kph increased drift by 40%."

Dr Butler-Ellis added the tests were carried out with a conventional sprayer and the results may be different for a sprayer equipped with a form of air-assistance.

However, Dr Butler-Ellis explained the effect is reversed when orchard spraying with air-assisted sprayers using a fixed air output.

"In this instance, the trees formed a barrier on both sides of the sprayer and tended to force spray droplets upwards," she explained. "By spraying at a higher forward speed, the drift problem in orchards was found to be reduced."