'Magic eye' slashes costs by Bernie Reppel

The magic boxes that make the weed-detecting sprayer work.

A 24-METRE (80 ft) spray boom that uses optical sensors and infrared and near infrared technology to spray weeds, not bare soil, is saving so much herbicide that it looks like paying for its $155,000 cost in three years.

Early results from the sprayer, developed by the Brownhill family with support from the Farm Innovation Program, indicate the potential to slash the annual glyphosate bill by almost 50 per cent.

It slashes water use to the same extent — "significant when using rainwater" — and opens the way for reduced reliance on glyphosate and economic use of more expensive herbicides to control hard-to-kill weeds like bindweed.

Gordon and David Brownhill crop 3,800 hectares to durum and bread wheats, faba beans, chickpeas, barley, sorghum, sunflowers, summer legumes and irrigated maize at Spring Ridge, on the Liverpool Plains south of Tamworth, NSW.

"It's virtually all zero-till, cultivating only as a last resort, and some paddocks have been zero-till for 13 years," David Brownhill said. That means a heavy reliance on herbicide to manage fallows. As an example, wheat following sorghum has a fallow length of 15 months, 7-8 spray applications, and application rates of glysophate of between 400 ml/ha to 21/ha.

"Our annual usage of glyphosate has been 22,600 litres. Estimated glyphosate savings are nearly 11,000 litres, which equates to approximately $50,000 annually. (See table.)

Standard practice and herbicide savings with sprayer. 2003. for Merrilong Pastoral Company
Crop Previous cropFollow lengthSpraysApplication rateTotal glyphosate l/haHectaresTotal litres
Wheatfollowingsorghum15 months7 to 8400ml-2.0 l/ha78005600
Sorghumfollowingsorghum7 months3 to 4600ml- 1.6 l/ha4.56502925
Sorghumfollowingwheat11 months5 to 6600ml- 1.6 l/ha5.211505980
Wheatfollowingwheat7 months3 to 4600ml- 1.6 l/ha4.53501575
Barelyfollowingwheat7 months3 to 4600ml- 1.6 l/ha4.52501125
Sorghumpre-harvestspray   218003600
Flood irrigation     36001800
Crop Previous crop

Total glyphosate l/ha

HectarsTotal litresTargeled % savingTotal glyphosate l/haTargeled % savingChemical saved/ litres
Sorghumpre-harvestspray218003600 360000
Flood irrigation  36001800    
    Total22605  Savings10951.5
Conclusion - estimates  
Estimates of savings11,580 Glyphosate litresat 80% saving and
 5,625 Glyphosate Iitresat 30%, saving
Glyphosate saved1,0951.5 litres$ 4.50 per Iitre
Estimated dollars saved $49,282 annually

"On the Liverpool Plains now we are using 3 1/ha of glyphosate to control bindweed at a cost of $13.50/ha spraying 100 per cent of the paddock. Using glyphosate at 1.5 1/ha and Starane at 750 ml/ha and spraying only 20 per cent of the paddock would cost only $4.46, a saving of $9/ha and using a chemical that will do a better job."

Spray weeds, not the paddock

The Brownhills have long believed they needed to spray "weeds, not the paddock". Weed density and type trials by NSW Agriculture showed that, at any one time, only 17 per cent of each square metre had weeds growing on it, while the brothers were still spraying 100 per cent of the paddock.

Since commissioning the machine in August 2002, they have sprayed 4,110 hectares and used an average of 17.5 per cent of chemical per hectare for a net saving of $20,311. Water saving was 135,200 litres.

Mr Brownhill first investigated the Patchen system and technology while in the United States on a Nuffield Farming Scholarship. The team at Merrilong — "especially Scott Jameson and Gary Crobie" — designed the boom themselves. "The Patchen Weed-seeker is designed to spray only the green plants, not bare ground. It has its own internal light source, so it can work during day or night, and is easily adaptable to existing spray systems.

"Wheels are spaced along the boom's 80-foot (24 m) length, to keep its height consistently at 24-26 inches (600-625 mm). The 64 sensors are spaced 15 inches (375 mm) apart and have a field of view of 16 inches (400 mm).

"It has two controllers, the biggest sprayer Patchen had built until now had been only 40 feet (12 m). We are running two identical 40-foot (12 m) systems," Mr Brownhill said.

On the trail of chlorophyll

The Weedseeker's optical sensor measures infrared and near infrared reflectance and the presence of chlorophyll, detecting any green plant but unable to distinguish between crops and weeds. When the Weed-seeker detects a green plant, it activates a solenoid that turns the spray nozzle on and off.

Gordon and David Brownhill say they're happy with the initial results from the Weedseekers, but are still learning and confronting issues like boom design and height for maximum sensitivity so it can see weeds as small as a thumbnail. It now consistently can sense weeds half the size of a man's fist. Grass weeds are more difficult to detect.

The 64 Weedseeker units cost Merrilong Pastoral Company $120,000, boom manufacture $16,000, fit-out and commissioning $5,000 and the spray tank $14,000, totalling $155,000.

Program 6 Contact: Mr David Brownhill 0427 255 609 email mpc@northnet.com.au

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