If spraying under normal conditions where wind speed is between 1-5 metres per second, the actual wind speed should not make much difference. Nevertheless, avoid spraying when winds exceed 10 metres per second. Dead calm conditions may lead to more local drift due to slow moving eddies. This was monitored over three years on the research orchard at Rukuhia and commercial Bay of Plenty blocks. Shelter reduces drift by up to eight times compared with no shelter.
Natural shelter is more effective than artificial shelter.
Some spray does penetrate through the relatively open bottom part of natural shelter, but this is not significant more than 8 metres from the shelter belt. No, the amount of drift is similar whether spraying concentrate or dilute for correctly set up airblast sprayers. If the helicopter rigs are well set up and operated they can be efficient at spraying the target area. Measurements of drift from helicopter spraying showed only low levels of drift, no higher than from typical ground spraying. However the potential for serious drift is much greater if there are high winds or there are errors in the targetting of the spray.