Twin cap nozzles recommended for spraying pre-emergence herbicides
The use of twin cap nozzles on sprayers when applying pre-emergence herbicides has been strongly recommended by College of Agriculture, Food and Rural Enterprise (CAFRE) advisers.
This was one of the key advisory points emanating from a recent National Register of Sprayer Operators (NRoSO) road show hosted by CAFRE at its Greenmount College campus.
CAFRE crops adviser, Leigh McClean explained: “The combination of different spray angles acts to deliver higher levels of ground coverage, particularly if soil clods are present.
“It is also recommended that tractor speeds are brought back a notch, again to make sure that as much of the ground is covered by the spray that is being applied.
“Decisions taken when selecting sprayer nozzles are complex. And at the end of the day, it is very much a question of balance," he added.
Issue that arise when opting for a specific nozzle type include the crop that is to sprayed, the stage of growth, and the droplet size of the product to be applied.
As a rule of thumb, the finer the spray: the greater the degree of coverage that will be secured within the crop.
However, sprays with a very fine droplet size are more prone to drift, the advisor said.
In contrast, coarse droplets will deliver reduced levels of leaf coverage but will be less prone to drift.
Products with an intended systemic mode of action are more effectively applied using nozzles that deliver a larger droplet size.
The role of air induction nozzles was also profiled at the NRoSO. They act to draw air through side holes into an internal mixing chamber.
This air mixes with the pressurized spray liquid, creating larger, air-filled droplets.
These coarse, low-density droplets reduce drift by 75-90% compared to conventional nozzles, as they are less susceptible to wind.
Crop penetration
Meanwhile, high crop densities can act to significantly reduce the amounts of spray penetrating a crop.
One way of getting of around this is to blow air through the crop as the boom is passing overhead, thereby opening up the various layers of the crop for the purposes of spray penetration.
A number of modern sprayers provide this facility.
Spray drift can be reduced by increasing the number of nozzles located along a boom.
A boom height of 50cms above the top of the crop is regarded as optimal for most spraying purposes.
However, this figure can be reduced if the number of nozzles delivering spray is increased.
