REVIEW: DAFF Dual Herbicide Sprayer

By: Tom Dickson, Photography by: David Gilchrist, Video by: David Gilchrist

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When cane growers asked for a fuss-free and effective sprayer, the Queensland agricultural department went to work and came up with the innovative dual herbicide sprayer (DHS). Tom Dickson checks it out.

At the Case IH Step Up! Conference hosted by Queensland young farmer group Next Gen in March, the panel discussed deep banding fertilisers to prevent the surface run-off of nitrogen and other nutrients into the water courses and out to sea, and more targeted spray techniques, which reduce the risk of residual herbicide loss while cutting costs.

One piece of equipment I am particularly interested in is the Dual Herbicide Sprayer (DHS) researched and developed by the Queensland Department of Agriculture, Fisheries and Forestry (DAFF).

The technology is being tested at Adrian Darveniza’s 600-acre (243-hectare) sugar cane property at South Johnstone, near Innisfail to the south of Cairns.

As we travel to the property I am expecting to find a substantially sized spray rig and boom and that’s exactly what I find. But the all-important attachment, the dual herbicide sprayer bar, is just a small stainless steel bit of apparatus with a few nozzles measuring about eighty centimetres long.

Employed as extension officers for DAF, Jack Robertson and Allan Blair are working together to develop the new dual herbicide spray bar, which they say is the critical component of the sprayer.

Blair says the dual herbicide spray bar was developed in response to cane growers’ requests for a simple, inexpensive spray system.

"Cane farmers were looking for a system for applying non-residual herbicides like glyphosate and Roundup to the inter row while utilising pre-emergent residual herbicides for the row," he explains.

"The dual herbicide spray bar is a non-shielded, strip sprayer that can direct one herbicide to the inter row and another to the row.

"The idea is it can replace the usual mix of more expensive residual cane herbicides which have to be sprayed over the whole paddock.

"It can be fitted to an existing Irvin type boom spray and is particularly useful for controlling difficult weeds that occur in the inter row, such as sour grass and guinea grass."

There are three spray bar designs to reflect the different row spacings commonly used in sugar cane production in Queensland. The spacings are 1.4–1.5m, 1.65–1.7m and 1.8–2m.

The spray bars are designed to spray approximately 50 per cent in the row and 50 per cent in the inter row, but in reality they have a 5-10 per cent overlap between the two. 

Darveniza has an 800-litre Silvan linkage boom spray on the back of his John Deere running off the power take-off (PTO) and has mounted a 500-litre tank on the front with an electric pump.

Along the boom he has four DHS bars attached so can apply chemical to four inter-rows per pass.

0697_DHS Sprayer _ready For Work With John Deere

In the back tank he has a mixture of diurex and gramoxone. He applies this residual mix to the row with 200 litres per hectare of water.

The dual herbicide spray bar allows him to simultaneously apply 2 litres per hectare of glyphosate with 50 litres per hectare of water from the front tank.

A key element to the successful operation of this revolutionary piece of spray apparatus seems to lie in the choice of spray nozzles. It is the use of air induction nozzles that reduces spray drift to virtually zero.

This is pretty critical, as any drift of glyphosate onto the sugar cane will result in yield loss and crossover of the residuals with the glyphosate will reduce the effectiveness of the glyphosate.

A quick demonstration of the spray pattern on the bare ground out front of Darveniza’s shed shows perfect placement of spray. For this exercise we place red dye and water in the back tank to represent the residual spray and yellow dye in the front tank for glyphosate.

As soon as Darveniza turns on the pumps and starts moving forward he leaves behind perfect strips of spray. The yellow strip representing the inter-row spray creates a one metre wide band and each red side spray strip for the cane row targeted is about 400mm.

Out in the paddock the dual sprayer gives an even better account of itself. We are working in sugar cane that has been struggling a bit due to early weed infestation. It’s about 1m high and starting to recover as a result of an earlier application.

This follow-up spray shows how perfectly the DHS applies chemicals out in the field. The inter-row is coloured yellow and the sugar cane row is coloured red at an even 400mm either side of the base of the cane.

Darveniza says he has reduced his costs dramatically by using glyphosate instead of a more costly blanket spray of residuals, but he adds the long-term benefits to the environment and the Great Barrier Reef are immeasurable and cannot be ignored.

It is a really simple piece of machinery and if you put the time in to setting it up correctly I can see you will get excellent results. My initial thought is why, did it take so long to come up with such a simple design with so much potential, but that’s probably what they said about the wheel.

For the detailed test report, pick up a copy of New Farm Machinery magazine issue 21, on-sale April 27.

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0619 DHS sprayer old and new On the left is the new Dual Herbicide Sprayer spray bar attached to the existing parallelogram spray arm and on the right is the old style single herbicide spray bar. 0619 DHS sprayer old and new
0633 DHS sprayer air induction nozzle An air induction nozzle is mounted in the centre of the bar for non-residual herbicides such as glyphosate. 0633 DHS sprayer air induction nozzle
0672 DHS sprayer workshop Darveniza and Dickson stand in the workshop where much of the DHS spray bar fabrication took place. 0672 DHS sprayer workshop
0697 DHS sprayer ready for work with John Deere Attaching new DHS spray bars onto the Irvin type boom. 0697 DHS sprayer ready for work with John Deere
0749 DHS sprayer tested with food dye Putting food dye in the spray mix shows the accuracy of the spray bar. 0749 DHS sprayer tested with food dye
0805 DHS sprayer spraying The air induction nozzle sprays a yellow mix of glyphosate to the inter-row and the red coloured residual is applied the cane row. 0805 DHS sprayer spraying

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