Depending on the application and working principle of the chemical (systemic, contact) a nozzle must be selected that meets the requirements of the application in question (droplet size and volume). To this end, first check the packaging of the crop protection chemical for specific instructions on the amount of spraying liquid to be used per hectare and the droplet size. If necessary, consult your dealer of crop protection chemicals.

Crop protection chemical packaging may give specific instructions on the amount of spraying liquid to be used per hectare, and the droplet size. However, this advice is based on the use of normal, hydraulic nozzles. However, the TwinFluid air and liquid system, which works with lower spraying volumes, can be applied for virtually all spraying work because finer droplet sizes can be applied effectively and without drifting.

During spraying, droplets of various sizes are formed, the droplet spectre. Not all droplet sizes are desirable. Tiny droplets are easily blown away to land in undesirable places. Spraying with too large droplets often means a waste of chemicals. They render inadequate coverage, attach poorly to the surface of the crop and will roll off.

The droplet spectre depends on the nozzle (spray angle, nozzle size and nozzle type) and the spraying pressure (liquid and air pressure).

In dry weather conditions (high temperature and/or low humidity), the evaporation rate is high, reducing the size of the droplet before it is deposited on the target. It is therefore recommended to avoid spraying at low humidity levels (below RLH 50%) as much as possible. If spraying is required anyway, spray a slightly coarser droplet. To achieve the same coverage, a slightly

Required coverage per type of spraying

As the distribution over the entire crop is never the same, the target is set to 100 droplets per cm ² .

The quantity of spraying liquid required for a specific coverage depends on the droplet size (theoretically calculated for a uniform droplet size and without loss of spraying liquid).

Quantity of liquid in relation to coverage

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You should take due account of the actual foliar index (foliar surface/surface area). The foliar surface per hectare may increase from e.g. 0.1 to 6 ha due to the growing of the crop. Accounting for the underside of the leaf as well, the surface to be covered is doubled once again.

For example, it is necessary to spray a crop with a foliar index of 5 and a droplet size of 250 micron. The quantity of spraying liquid required for a coverage of 100 droplets per cm ² amounts to (5x82) = 410 l/ha. However, if you can spray (effectively and without drift) with 150 micron droplets, much less spraying liquid will be required, namely (5 x 18) = 90 l/ha.

In addition to the number of droplets per cm ² , the degree of coverage in % is also important. A smaller droplet covers a smaller surface than a larger droplet. Therefore, this droplet also has to spread out to obtain the same degree of coverage. If the foliar surface is fatty or hairy, a surfactant may be added to the chemicals. In this way the degree of coverage is increased by e.g. 20x when the contact angle is reduced from 160° to 60°.

Different droplet size spectre measuring systems produce different results. Therefore, it has been

Droplet size classification according to Imag-DLO

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