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Good sources of information on how agrochemicals should be applied are often found on the agrochemical label.
You may still need to adjust your sprayer to the specific spraying conditions you choose for volume rate, driving speed, nozzles and spray pressure.
Check driving speed:
1) Half fill the spray tank with water.
2) Mark out 100 m – note time to drive the distance.
3) Driving speed formula
Example:If it takes 50 seconds to drive 100 metres then the spraying speed is 7.2 km/hour.
1) To find the right nozzles use our Nozzle Selection Tool.
2) Use the calibration disc or formula (nozzle spacing 50 cm):
Example: By aligning 150 l/ha and 7 km/h on the calibration disc the line in the "window" (l/ha) shows that we need a flow of 0.875 l/min.
Then a suitable combination of nozzle size and pressure can be found on the lower half of the calibration disc: ISO 025 at 2,3 bar (or ISO 02 at 3,6 bar).
If using the formula: (7 km/h x 150 l/ha)/1200 = 0.875 l/min
- Nozzle and pressure to obtain 0,875 l/min can also be found in the HARDI nozzle catalogue
Check liquid system:
Check nozzle output
For many years, 7 to 8 km/h [and 4 to 6 km/h in dense crops where canopy penetration is needed] have in general, been considered good practice. It is an option that is still of value for today.
Increasingly, it is recognised that the slower the boom moves then the less the turbulence is around it, and hence, less drift and less disturbance to the quality of spray distribution.
Some important considerations needs to be made before choosing a higher tractor gear:
|Side effects from higher speed:
||How to deal with the side effects:|
|1) More turbulence / more wind drift
||Bigger droplets or TWIN air assistance|
|2) More boom movement||Often the boom should be readjusted for optimum performance at a higher drivning speed|
Spray pressure influences spraying effectiveness in crops by 3 ways:
Pressures recommended for field spraying with standard and lowdrift nozzles
Pressures recommended for field spraying with INJET nozzles
The droplet spectrum
All agricultural nozzles produce a range of drop sizes. This is a useful feature as the crops to be sprayed always present a 3-dimestional target that have contrasting leaf surfaces and angles. Hence, in a crop canopy, for example, finer droplets are likely to be deposited in the top and larger droplets lower down.
Drop sizes are measured in micron. 1 micron = 1/1,000,000 metre.
To describe the median droplet sizes produced from a specific nozzle, the term VMD is used.
VMD = Volume Median Diameter
VMD is the mid-way drop size that is reached when the accumulated volume of smaller drops accounts for 50% of the sprayed liquid leaving the nozzle; half the volume is atomised into droplets smaller – and the other half of the volume is larger - than the VMD.
Wind drift has in the past been regraded as being mostly caused by droplets below 150 micron in diameter.
Be prepared to optimize spraying technique “on the go”
Rather compromise on drop size than timing.
In many applications - from fungicide spraying in potatoes to dicotyledonous stage, broad leaf weed herbicide treatments -timing is very critical. Here a delay may often prompt the need for a higher dose or an increased number of applications.
The potential efficacy loss due to an increased droplet size - that offers less drift risk - will be less dramatic, as long as a good liquid distribution is maintained. Hence it is a good idea to have a set of low drift nozzles or INJET nozzles ready on the nozzle holders in case wind speed increases – and is a lot more convenient and safer than returning with a half full spray tank. Because there can be up to 10% difference in flow for new and worn nozzles both sets of nozzles should be calibrated - even if both sets are ISO nozzles.