Salient reminder of productivity push

29 Mar, 2014 01:00 AM
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 GRDC-sponsored New South Wales spray consultant Bill Gordon packed a wealth of knowledge into a spray workshop at Binnu last week, including a practical demonstration of nozzle selection.
The more hectares an hour you can do the better for timing issues...
GRDC-sponsored New South Wales spray consultant Bill Gordon packed a wealth of knowledge into a spray workshop at Binnu last week, including a practical demonstration of nozzle selection.

IT was back to the future for many farmers listening to GRDC-sponsored New South Wales spray consultant Bill Gordon at last week's Crop Updates regional meeting at Binnu.

His opening message was all too familiar to farmers pushing the envelope to maximise spray programs.

"Everybody is scaling going wider and faster," he said.

"But does it work to gain efficacy?

"You are aware of efficacy trials but most are done at 4km/h, whereas you are spraying anywhere between 16kh/m and 25km/h and even faster.

"The more hectares an hour you can do the better for timing issues but it can also mean more risk of drift, especially if weather conditions are not right."

Mr Gordon said the importance of recognising and avoiding surface temperature inversions could not be overstated, along with correct nozzle choice for optimum deposition.

"There's an interaction between boom height above the target and operating speed, especially when spraying at night," he said.

"The higher the boom and the faster the speed the more (spray) you leave in the air.

"And during a surface temperature inversion the airborne droplets can travel very long distances, particularly, if you're spraying fungicides.

"It's very difficult to be flexible to gain the optimum coverage and efficacy when conditions can change hour by hour.

"I recommend having two sets of nozzles and while it's expensive, it's so critical for night spraying in inversion conditions.

"You can do the cut outs first then do the rest of the paddock at speed (within limits)."

According to Mr Gordon, fast travel speeds have three main effects on how spray behaves after it leaves the nozzle.

"Faster speeds increase sheet break-up and cause a finer, more drift-prone spray to be produced," he said.

"Fasters speeds also cause the sprays to stay aloft longer because it gets swept back due to air resistance."

Mr Gordon said he recommend air induction nozzles where practical because of better deposition and drift management.

"They offer opportunities but they're not for everybody," he said.

"They can suck in dirt and can inhibit nozzle performance.

"You've got to decide what nozzles suit the product you are spraying and at what spacings and water volume.

"The GRDC Back Pocket Guide is an excellent reference for nozzle selection."

Mr Gordon said a set of nozzles was required behind wheels, not just one.

"Test strips show that one metre out from the wheel, deposition is poor so a set of nozzles is required to ensure you get the coverage," he said.

Improved deposition around the wheels can be improved by higher clearance sprayers, front-mounted booms and higher applications volumes.

"The latter makes a huge difference," Mr Gordon said.

"Remember that poor deposition and dust means weed survivors and seed set."

Boom height control was very important to improve droplet deposition into standing stubble.

"A cross wind is a big factor and the use of nozzles at the smaller end of the Coarse (size) spectrum," Mr Gordon said.

Other factors included narrower nozzle spacings (25cm instead of 50cm), higher water rates (greater than 60L/ha with 80L/ha optimal), minimising boom height (but must be at least double overlap) and slower travel speeds.

Mr Gordon's take-home messages:

p Night spraying is high risk for spray drift.

p Efficacy will be affected more by target conditions (stress), rate of product and application volume, than time of application, in good conditions.

p Application volume and spray quality must match the products' mode of action, the target and stubble load.

p High spraying speeds cause problems for effective deposition, not just wheel tracks.

p Newer spraying systems are available to help manage spray quality when large speed variations are likely.

"But growers need to know the strengths and limitations of each system to know what might suit their farming system," Mr Gordon said.

"It is really important to have the correct boom height and boom stability, then make nozzle selections for faster turnarounds."

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Ken Wilson

Ken Wilson

is Farm Weekly's machinery writer

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