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.

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. A smaller nozzle opening will produce a smaller droplet. A high operating pressure mainly causes nozzle wear.

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 higher amount of liquid is required. To this end, select a coarser nozzle or a lower driving speed. The quantity of chemicals can remain the same. The number of droplets required per cm ² on the surface of the foliar surface depends on the type of spraying and the chemicals.

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

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.

Suppose, you have to perform a spraying in a crop with a foliar index of 5 and a droplet size of 200 micron. The total crop must be covered. The quantity of spraying liquid required for a coverage of 100 droplets per cm ² amounts to (2 x 5 x 42) = 420 l/ha.

AG,WZ00009,196 -19-18FEB02-1/2

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°.

The Crop Protection Manuals give information on the quantity of liquid (in l/ha) and on the droplet spectre with which optimal results are obtained in different sprayings. This information is usually represented by a code. The code consists of a digit (for the output) followed by a letter (for the droplet size). Code 4M, for example, means that it is recommended to spray at 400 l/ha with a nozzle which upon dosing produces a droplet size from the "Medium" spray quality.

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

Droplet size classification according to Imag-DLO

AG,WZ00009,196 -19-18FEB02-2/2