Selective spraying to cut costs

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A new permit in place across Australia will help growers tackle herbicide-resistant grasses with weed-detecting technology

Simon Tiller, a grower from Esperance in Western
Australia, adjusting his WeedSeeker® boom spray.
It uses infrared sensors to identify and spray weeds.

PHOTO: Evan Collis

Increased use of no-till cropping and an increasing incidence of summer rain have stimulated many growers to include a predominantly glyphosate fallow over summer to remove weeds and conserve moisture for the next crop.

To reduce the risk of glyphosate resistance developing in fallow weeds some growers are using weed-detecting technology to detect individual weeds that have survived the glyphosate application and spraying these with an alternative knockdown herbicide.

The key to successful resistance management is killing the last few individuals, but this becomes rather difficult on large-scale properties. Left uncontrolled, these last few weeds result in significant seed production and a resetting of the weed seedbank.

The introduction of weed-detecting technology is timely as it is well suited to detecting patches of weeds across large areas. Sales of the two systems available in Australia, WeedSeeker® and WEEDit®, have increased by at least 30 per cent annually over the past two years.

The technology uses optical sensors to turn on spray nozzles only when green weeds are detected, greatly reducing total herbicide use per hectare. The units have their own light source so can be used day or night.

Rather than spray a blanket amount of the herbicide across a paddock, the weed-detecting technology enables the user to apply higher herbicide rates (per plant), which results in more effective weed control and saves on herbicide costs.

Special permit

Weed-detecting technology (via WeedSeeker®) is being used to manage glyphosate-resistant grasses in northern NSW fallows with the aid of a minor use permit. This allows growers in the region to use selective grass herbicides and higher rates of paraquat and diquat (bipyridyl herbicides, Group L). The permit (PER11163) is in force until 28 February 2015 to cover all Australian states and will be reviewed annually.

The permit allows the use of about 30 different herbicides from groups with seven modes of action. Additional modes of action are likely to be added to the permit over time.

Some herbicide rates have been increased to enable control of larger or stressed weeds. For example, the glyphosate 450 (450 grams of glyphosate per litre) rates range from three to four litres per hectare (using a set water rate of 100L/ha), which far exceeds the label blanket rates of 0.4 to 2.4L/ha. Similar increases in rate have also been permitted for paraquat (Gramaxone®).

The WeedSeeker® permit system is a lifesaver for zero and minimum-tillage systems battling glyphosate-resistant weeds as it represents a more economical way to carry out a double knock and avoids the need to cultivate for weed seed burial.

The new technology also has the potential to map troublesome weed patches so that these areas can be targeted with a pre-emergent herbicide before sowing.

More information:

Tony Cook,
02 6763 1250,
tony.cook@industry.nsw.gov.au

End of Ground Cover Supplement Issue 104
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Region National, North, South, West