The way to spray

Whether it’s for spot-spraying weeds like ragwort and thistles or spraying out paddocks for cropping or regrassing, a spraying system is an essential piece of equipment on most dairy farms.

The impressive range available goes from a 35-litre spot sprayer for the quad to a GPS-guided unit carrying more than 2000 litres and with a 24-metre boom. The trend is to bigger, more sophisticated, more versatile sprayers with improved accuracy. Farmers planning to buy a new sprayer will find there’s a lot to consider.

Two common sprayer scenarios are the 12-volt spot-sprayer mounted on or trailed by a quad, UTV or ute; and a larger-capacity tractor-mounted or trailed boom sprayer. The smaller spot-sprayers are usually off-the-shelf, while the bigger units are modular and tailor-made to farm requirements. Defining the farm’s requirements, using a checklist like this one from C-Dax customer service representative Richard Brown, is the first step in identifying a suitable sprayer:

• What do you want to do?
• What type of weeds?
• Spot, boom, or wipe?
• What are the proposed application rates and vehicle speed?
• What type of vehicle is to be used?
• What area is to be sprayed?
• Is a guidance system like foam marking, spray control, Teejet Matrix or GPS to be included?
• What terrain is to be covered?
• Is the sprayer to be used for liquid fertiliser, bloat spray, zinc or other applications?

Spot-sprayers:

Vehicle: Spot-sprayers are mounted on a quad carrier, UTV or ute deck, or trailed by one of these vehicles.

Quad sprayers might have a flat tank moulded specifically to fit a quad carrier, or might be a flat-deck sprayer. Quads without power steering are better to have a spraying system mounted on their rear carrier, because the extra weight of the sprayer and spray on the front carrier makes steering heavier. And most quads can carry a heavier load on their rear carrier. A tank can be fitted to the front carrier of a quad and connected to a spray system on the rear carrier.

Flat-deck sprayers are more adaptable because they can be moved from ute to UTV and quad, while a specific quad sprayer might not fit a different quad. Trailed sprayers have the convenience of not having to be loaded and unloaded onto a carrier or deck, and do not tie up a quad carrier. And a higher-capacity sprayer can be towed than carried on a quad.

Capacity: For spot-spraying, capacity is not as important as for boom-spraying. A smaller unit on a quad means less weight and therefore better stability. The quad manufacturer’s recommended carrier weight should not be exceeded, although some sprayers recommended for quads by sales people exceed most of the maximum loads specified. The Honda TRX500 for example, has a maximum loading recommendation of 40kg on the front carrier, 80kg on the rear carrier, and 385kg towed. Spray, being liquid, will affect stability more than a static load on hills and cornering.

Safety: The low centre of gravity of dedicated quad carrier spray systems, and internal tank baffles, will reduce instability.

Hardware: Pumps, reels, hose, hand guns and other components vary in quality, capacity and price. You generally get what you pay for. Cheaper units usually have smaller pumps, no reel, shorter hoses and poorer-quality hand guns. One trailed unit promoted for quads has wheels so small it looks like it could only be used on concrete. Where use is to be very limited, a cheaper unit may be appropriate, but few of us regret buying something a little better. Often it’s not until we use something that we realise its true potential and it gets a lot more use than intended.

Pump: Capacity is important, especially if a boom system might be added to the unit. And if this boom system might be used for products like liquid fertiliser, this should be mentioned to suppliers. The pump should be mounted in a low position to prevent priming problems, and in a position where damage is unlikely.

Filtration: Filters to prevent nozzle blockage may be in the tank filler, pump suction, and gun handle. Filters should be readily accessible and easily cleaned.

Hose and gun: Length and pressure rating of the hose should be checked. Hose storage may be by looping around the tank or a more convenient reel. Gun quality and nozzle adjustment vary and are critical to hassle-free and accurate spraying.

Boom sprayers:

Vehicle: Bigger boom sprayers are either tractor-mounted or trailed. Tractor-mounted sprayers are PTO-driven, while the trailed units are either PTO-driven or have their own petrol engine on board. PTO-driven units tend to be cheaper than those with an engine. The terrain to be covered will also influence the choice between mounted and trailed.

Boom: Boom lengths vary from eight to 24 metres although dairy farm units usually have boom lengths of about 12m. Self return breakaway of booms prevent damage and minimise disruption to spraying. Sectional spraying which directs spray to selected boom sections prevents overspraying. A boom suspension frame reduces the shock exerted on booms as terrain varies. Self-levelling booms allow more accurate spraying as ground slope changes. Boom lift allows wing sections of the sprayer to be raised to allow for side slopes. Folding of booms may be manual or hydraulic. Foam markers may be fitted to one or both boom ends. Double foam markers allow for end-to-end spraying, where the tractor direction is reversed, while a single marker is suitable for “round and round” spraying. Boom operation may be manual, or controlled from the cab electrically or hydraulically, to fold, lift and tilt.

Nozzles: Check valves in the nozzles prevent dripping onto non-target areas. Protection of nozzles by a panel or guard prevents damage. Consideration in nozzle selection should be given to spraying chemicals like liquid fertilisers.

Accuracy and efficiency: Accuracy is a significant factor in boom spraying and is subject to factors like vehicle speed and nozzle wear. Auto rate control allows more precise spraying. Teejet Matrix gives steering guidance based on boom length, while GPS technology provides the ultimate in accuracy and allows night spraying when the wind has usually dropped.

Optical spot-spray technology is to be introduced to New Zealand by Croplands. This uses near-infrared camera sensors to detect the green leaves of weeds in fallow paddocks. The sensors activate solenoids for specific nozzles to target the weed picked up by the sensors.

Controlled droplet application (CDA) optimises droplet size by using rotary atomisers instead of nozzles, so the drift associated with smaller droplets, and the run-off associated with larger droplets, is minimised. More concentrated spray is used, so a larger area can be sprayed with the same volume, there is less ground contamination, and less drift.

Fertiliser spraying: Nozzles might need to be changed to spray liquid fertiliser. Some sprayers are fitted with liquid fertiliser-ready pumps, while other pumps might be unsuitable for some products like urea. The mixing and pumping systems should be checked if these products are to be sprayed.

General advice

Safety:
A low centre of gravity is desirable in most farm machinery, but even more so for liquid loads. A lower sprayer means the operator is less likely to have to climb on to it to add chemicals. Even better, a chemical induction probe draws chemical from its container on the ground into the tank by use of a venturi, avoiding lifting and pouring concentrate. A large recessed tank lid is more likely to contain spills. Baffles in the tank will reduce slop and so reduce instability.

Tank:
Tanks should be moulded in UV-stabilised materials which will prolong the life of the tank. Translucent tanks with an easily read scale allow ready volume assessment. Agitation is important for some products, so this should be considered. Some sprayers have an agitator fitted. The tank design should allow complete evacuation of the spray. Some tanks have a drain valve which can be opened from above the unit. Filling is more convenient through a hose which couples to the tank by a cam-lock coupling. On some units this also allows the sprayer’s pump to draw water from a source to fill the tank.

Cleaning:
Cleaning can be made easier with a chemical rinse tank. Some units have provision for flushing the boom with clean water between spraying sessions, with spray still in the tank. This means there is no contamination of non-target areas. A hand-washing facility is provided on some models.

Mechanical:
Frames should be robustly designed and made. A skid plate could be warranted on tractor-mounted units. Independent springs on trailed sprayers will reduce the shock to the towing vehicle. This is more important for smaller vehicles like quads and UTVs.

Sprayer use:
While the manual will provide comprehensive guidelines on the use of the sprayer, care, cleaning and calibration warrant special mention. Care is important as chemicals are handled and sprayed, so all precautions must be taken to protect the operators and the environment. Cleaning after use is important because this is the best way to prolong its service life. Calibration is important because nozzle wear can be quite significant and affects discharge rates, and this in turn increases chemical used.

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