The quality of a spray job rests on a number of parameters and the nozzle remains the farmers’ most important tool in order to influence the end result
Even with this in mind plant protection is sometimes treated as a bit of a compromise. Conditions change as crops are sprayed – nozzles allow farmers to react to these conditions.
The question, of course, is what makes the difference and creates the best result for crops? Sometimes the number of variables restricts definitive answers to these simple questions. One thing we do know though is that the application quality is largely influenced by the way the nozzle is used.
The nozzle lets the user control:
· The throughput and the dose
· Quality of distribution
· Drop spectrum and coverage
· Distribution over the target
· Drop retention or reflection
· The degree of drift and downwind fallout
Water volume and droplet size
Working capacity will largely depend on the water volume rate. Why? Because low water rates mean less filling time and transport are required. Even a volume rate reduction of 25 per cent increases capacity by more than 10 per cent. This represents a tangible difference, even in the short term. It is important however, to pick the right nozzle and the right speed for the job. Lower spray pressure alone will mean that both coverage and deposit are reduced. The application rate of a nozzle could vary +/- 40 per cent of the medium flow at 3.25 bar.
Droplet size is important and the farmers needs will differ according to conditions and type of crop. HARDI nozzles follow BCPC specifications with regard to droplet size classification. There are six sizes of classifications but for most types of farming only “fine”, “medium”, “course” and “very course” are relevant. The challenge is that no nozzle will give all the spraying options which is why knowing how to compromise is also useful.
Guidelines for chemical spraying quality
Choosing the right nozzle depends on the spraying job and the chemical. Sometimes the quality is given, but if not try using these guidelines:
· Use fine droplets for good coverage on vertical targets like grass weeds
· Use course droplets if you need to penetrate dense crops
· Soil applied herbicides depend on soil humidity and therefore droplet quality is not important
· Contact action mode needs finer droplets
· Use medium sized droplets for chemicals that are transported in the plants
The new directive from the EU states that a sprayer must be equipped with drift reduction nozzles. Drift reduction nozzles work with very course droplets; this is the only way to reach a high drift reduction level.
Due to the needed capacity ha/h and the standard volume rate l/ha the ideal nozzle size should be carefully chosen. The basic spray pressure should be between 2.5 and 3 bar. Volume rate demands could differ depending on crops and growth stages. Making minor adjustments can yield significant results and savings.