The 'three Ts' are key to effective pre-emergent spraying

Author: | Date: 18 Mar 2011

Bill Gordon and Allan Mayfield

The ‘three Ts’ are key to effective pre-emergent spraying

Grain growers throughout the southern cropping region are encouraged to consider the ‘three Ts’ when embarking on their pre-emergent herbicide spraying programs this season.

The target, the timing and the technique are the keys to an effective spraying regime, according to industry expert, Bill Gordon.

Speaking at the recent Grains Research and Development Corporation (GRDC) grains research Update in Adelaide, Mr Gordon said achieving success from pre-emergent herbicides was “about getting every part of the application process right”.

“There are no magic bullets when it comes to pre-emergent spraying,” said Mr Gordon, of Bill Gordon Consulting, Lawrence, NSW.

“Getting a good result is about doing all of the little things well, from product selection to match the weed spectrum present, through to monitoring the spray results carefully.”

Mr Gordon said the aim of any pre-emergent application should be to maximise the deposit onto the soil surface and to achieve a uniform distribution of the product across the soil surface.

“The evenness required will be dependent on the solubility of the product and its ability to move within the soil.

“The time between application and incorporation may also be very important – generally, the more volatile the product is, the more important it is to ensure incorporation occurs soon after application.”

To assist growers with the spraying programs, Mr Gordon emphasised the importance of the basic elements, the three Ts:

The target

“Know your target – it is critical to ensure that the product selected is the most appropriate for the weeds present and the situation,” Mr Gordon said.

“It is important to consider many factors, such as the previous weed burden, potential resistance, the product’s residual activity, solubility and soil moisture requirements, ability to tank mix, and the target area including stubble load and ground cover.

“Always consult product labels and refer to manufacturer’s technical data to make an informed decision.”

The timing

Mr Gordon said it was important to consider the most appropriate conditions for spraying a pre-emergent and when the incorporation will need to be completed by.

“Suitable conditions for spraying pre-emergent products are the same as for any spraying operation,” he said.

“Extremes of temperature, relative humidity and wind speed all affect the amount of product available to deposit on to the target area. Often these factors will interact with droplet size, speed and boom height.”

Mr Gordon advised growers to always refer to the product label for appropriate conditions for spraying.

The technique

Many small adjustments to the sprayer setup can improve the deposit onto the soil and minimise losses such as tie up on stubble and loss to atmosphere.

“The heavier the stubble load, the greater the need for a coarse spray quality or larger droplets. Larger droplets usually require greater application volumes (more than 80 litres/hectare) to ensure uniformity of the deposit, particularly for pre-emergent herbicides with a low solubility in the soil,” Mr Gordon said.

“There are many ways to deliver the desired spray quality and to achieve the desired application volume, which can require thinking about more than just the nozzle type.”

Mr Gordon said the best way for growers to maximise deposition was to conduct a test using water-sensitive paper.

“Growers can check the impact of variations in nozzle type, application volume, boom height and travel speed to compare their effects on deposition in and around stubble to determine what works best in their situation.”

In conclusion, Mr Gordon said good application technique would not prevent the development of herbicide resistance in weeds but it would allow growers to identify it much sooner.

“Hence application should be one component of an integrated weed management program.”

More information is available from Bill Gordon via 0429 976565 or or by visiting the GRDC’s integrated weed management information hub,


Caption: Consultant Bill Gordon (left) at a GRDC Update with GRDC Southern Regional Panel member Allan Mayfield.

• For more information, contact Bill Gordon on 0429 976565


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