Spraying tips and how-tos

Whether it be for weed control, pest control or fertilising, spraying is an essential part of the farming cycle.

The ultimate aim of spraying is efficient application of the chemical to the target, but there are so many variables involved that, in addition to achieving this prime objective, contractors or farmers also need to ensure they don’t inadvertently affect neighbouring operations in the process.

We spoke to several leading industry experts for their top tips on effective crop protection.

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This is perhaps the most important tip experts have to offer, because nozzle selection pretty much determines the efficiency of the spraying operation.

"If you do not get the nozzle selection correct, you will be throwing away valuable money and you could end up with bad spray application," said HARDI Australia's Peter Vella.

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"You need to understand what chemical you are applying: is it a contact, systemic or a soil incorporate?"

So how does one go about picking the right nozzle?

"For me, it's a three-step process," said Cropland's Jeremy Rennick.

"You need to think about the target you're trying to kill, the chemical you're using to kill it and the risk of drift.

"The aim at the end of the day is to get as good a level of efficiency as you can, kill what you're trying to kill while reducing your drift as much as possible."

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The target could be a weed, insect, rodent or any type of pest that could harm the crop, and taking that into consideration is of utmost importance. The chemical could be a herbicide, insecticide, pesticide or fertiliser, and they are generally classified as either contact or systemic.

Contact chemicals would require full coverage on the target to kill it, while systemic gets absorbed into the plant and, in comparison, does not require as much coverage.

"For example, if I was chasing broadleaf weeds with a systemic chemical, I can go with a coarse spray quality because I've got a big target and I don't need to cover the target in the chemical," Rennick said.

"But I would also need to look at drift risks. So if I was in an area with other sensitive crops around me, I would go with an ultra-coarse spray quality."

Nozzle manufacturers usually have a chart farmers can refer to in order to determine which nozzle is right for them.

"A farmer might say he wants to put out 70l/ha at 20km/h, and a nozzle chart will tell you, at 20km/h, which nozzle puts out that amount of chemical," said Goldacres' Stephen Richards.

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“Air-induction nozzles produce air-filled droplets that shatters into smaller droplets upon contact so it gives you good coverage with a coarser output.

"The most important thing is to be wary of drift. All nozzles can spray but it's all about getting the right one to ensure it gets to the target."

To determine which chemical to use, you need to first determine what it is you are trying to achieve or what it is you are trying to kill. Is it a total knockdown, pre-emergent, post-emergent, fungicide, insecticide or fertiliser application?

An agronomist can inform you on which chemical to use for your application but an important thing to do is to check that the chemical is registered and is suitable for the target you're trying to address.

"Every chemical that's sold in Australia is registered with the Australian Pesticides and Veterinary Medicines Authority (APVMA)," Rennick said.

"On the side of every chemical drum sold there's a label, and it's an important piece of information to have. People need to read that label and ensure that it's going to do what they want it to do."

Check that all your lines, booms and tanks are clean and decontaminated, and that there are no leakages in the fittings or nozzles.

A calibration of the sprayer is always a good idea to ensure everything is at the right setting for the operation ahead.

"As most systems these days are able to accept GPS speed as the primary input, there is no need for a physical calibration," explained Vella.

"However, if your system is using a traditional speed sensor mounted on the wheel of the sprayer, then a calibration is required."

There are several key things to calibrate for an efficient calibration spraying operation: travel speed, spray pressure, sprayer output and application rate.

By checking the output you are also checking for nozzle wear, which is important so you know when to replace them and avoid under applying or over applying. Some sprayers have flow sensors at the nozzles to check the flow rate, but an old-school method is a jug test.

First, find out what flow your nozzle should be putting out per minute – for example, 1l/min at three bar pressure. Hold the jug under the flowing nozzle for one minute and record how much liquid you get.

Finally, compare it with the nozzle specifications. If the nozzle put out 1.2l/min instead of 1l/min as it should in good conditions, it means the nozzle has worn out and requires replacement.

"Nozzles do wear quickly, so people should be checking their nozzle flow at least twice a year. But I'd prefer to do it four times a year," Rennick said.

Arguably the most crucial factor in any spraying operation concerns weather conditions, and wind plays a massive part.

Too much wind, and you will cause drift. No wind, and the chemical will remain airborne and not hit the target efficiently, while also drifting off into the distance and potentially into unwanted areas.

"Be mindful of changes in the wind direction and speed; always keep in mind what effect this will have on your buffer zones and spraying near sensitive areas or crops," Vella said.

Be very wary of spraying at night as conditions could be too still and a temperature inversion could occur – this is when a layer of cool air is trapped underneath warm air. When spraying at this time, the chemical droplets could get trapped underneath the layer of cool air and not reach the target effectively, before drifting off to other areas long after spraying.

Also be aware of spraying at sunrise, as dew point could be high and the chemical won't be able to penetrate the target effectively.

As a general rule, the most effective time of the day to start spraying is after sunrise when dew has evaporated, and wind speed and direction has been consistent for 30 to 40 minutes. The best window to spray is from then until midday. After midday you can still spray, but be mindful of high evaporation risk and constantly monitor wind speed and direction to ensure conditions do not become unfavourable.

As suitable conditions for spraying change, you need to consider doing something to minimise the risks involved.

"Let's say you're using a coarse spray quality, and the risk has gone up," Rennick said.

"Instead of keeping on with the coarse spray quality, go something bigger like an extremely coarse spray quality – this will give you a bigger droplet that's not going to drift and will be taken down into the ground."

Another factor to watch out for is Delta-T, which is the relativity between temperature and humidity, calculated by subtracting the wet bulb temperature (thermometer with a moist cloth) from the dry bulb temperature (normal thermometer).

"The important thing to keep in mind is, there is no such thing as no drift," Rennick said.

"There's always some amount of drift. You might get it down to one or two per cent, but don't ever think there's no drift. The best thing is to mitigate it the best that you can."

"It's important to have a system that gives you a recording of your spraying jobs just so you can cover yourself if something goes wrong," Goldacres' Stephen Richards said.

"If your neighbour comes and accuses you of killing their crops and you don't have a record, you're buggered."

Good record keeping also means contractors are able to get a snapshot of the job they need to do on a property and be able to carry out their tasks without having to ask too many questions.

"From an agronomic point of view, one of the best ways to counter weed resistance is to keep mixing up your chemicals, so if you're keeping a record of what you're spraying, you might notice that a certain chemical has been used too many times and that you should use another one next time," Rennick said.

Before you start a job, make sure the correct details are logged, including operator's name, property name, the specific job required etc. Most good monitors designed to work with spraying allow for detailed record keeping and will log jobs accordingly, including information such as wind speed, spray rate and more.

Most technologies nowadays will also allow the transfer of data wirelessly, which reduces paperwork and increases efficiency.

Constant monitoring of the weather is paramount up until you park the sprayer in the shed.

To aid this, there are bolt-on weather stations or portable weather monitoring devices farmers can use to monitor any change in the weather conditions.

Things that might change include wind direction, which could be dangerous if there are sensitive crops nearby.

"All nozzles have a recommended pressure range and if they operate outside this range, you may increase the amount of drift," said Vella.

"Also, if you go below the recommended pressure, you are reducing the angle of the pattern and you may not achieve correct coverage."

Boom height should always be as close to the ground as possible to ensure the chemical gets to the target.

"The higher the boom is, the more drift they'll create and the worse job they'll do," said Rennick.

"The idea is if you've got 50cm nozzle spacings, you should be 50cm above the target or false target, which means stubble, or 50cm above the ground.

"There are sprayers with 48m booms now and unfortunately it's pretty hard to run a 48m boom at high speed, 50cm off the ground. There's a fair chance you'll hit the ground and cause some damage, so you definitely need to keep an eye on your boom height."

Once the job is done and it is time to put the sprayer away, it is very important to decontaminate the tanks, lines and the entire machine to ensure no chemicals or chemical residue remains. This is especially important if you are parking the machine up for a while, or will be moving on to another entirely different job.

"If you're doing a knockdown and then moving on to spraying grubs in canola, for example, you might kill the canola if you have some leftover chemical from your last spray, so you have to make sure everything's washed out pretty well," said Richards.

"You need to make sure that everything's flushed out and clean; the machine should be all washed and sprayed down with some oil because the chemicals you're spraying can be pretty harsh on the components and paint."

"It is also important to ensure that all filters are removed and cleaned along with your nozzles and nozzle filters," added HARDI’S Peter Vella.

"Spraying is a complex task as there are elements that we can and cannot control," said Vella.

"Ensure you have all the relative information so you make an informed decision for your operation.

"In regards to your equipment, ensure that everything is running at optimal levels and ensure you do the required maintenance on your sprayer.

"I strongly recommended a pre-season service of the sprayer every year; this will try and help with minimal downtime caused by failures."

Rennick agreed that attention to detail is of utmost importance.

"Don't assume that it'll be all right, because if you keep doing the wrong things, you simply won't do the job properly and that will cost you money and time," he said.

He added carelessness will ultimately cause grief for not just for the sprayer, but for other farmers as well.

"There are people out there that are a bit blasé and doing the wrong things and causing drift. What will happen eventually is we'll end up losing some chemicals because the government will ban them," he said.

"At the moment, farmers need all the tools they can get their hands on to do their job properly, so the last thing we want is for certain chemicals to be banned because it just takes another tool out of their toolkits.

"If people approach their spraying with the mantra that they've got to be as efficient as they can and that they need to reduce drift as much as possible, they should be all right."