Archive Article: 1997/04/17
DRIFT has always been a key concern when spraying and is reinforced by MAFFs recently revised Green Code.
"Drift outside the treatment area is a legal no no," stresses Paul Miller, spray technology specialist at Silsoe Institute.
But the need for timely applications can raise drift risks. Higher forward speed and lower water volumes can be culprits.
Tank mixing and adding adjuvants may also alter spray quality significantly, according to recent work at Silsoe Institute.
Such issues need taking into account on top of the traditional factors most operators concentrate on of wind, boom height and equipment maintainance.
Reduce drift
"The only way to control drift risk with a conventional fan nozzle is to increase droplet diameter, by using a lower pressure, alongside the highest possible droplet speed when it comes out of the nozzle. But that leads to conflicting pressure requirements," acknowledges Dr Miller.
It is important to keep within the recommended pressure range for a given spray quality, preferably working toward the lower end of the range, he notes.
Boom height should be kept 40-50cm (16-20in) above the soil, crop or weed, whichever is the highest.
Low-drift nozzles can reduce drift by producing a larger droplet size, Dr Miller notes. But size must remain within the spray quality required for the product being applied.
"They are particularly good for some low volume applications, such as residual herbicides," he notes. But they do not maintain efficacy of a product in a growing crop as well as air inclusion jets.
The latter seem more efficacious because of their aerated structure. But take care, he advises. "If either type is used at low volume on fine targets, such as blackgrass, insufficient chemical may hit each plant because there are just not enough droplets produced." *