by Peter Reading
The Crop Doctor
Grains Research and Development Corporation (GRDC)

Do you use glyphosate?  Well if you want to keep using it you must use it responsibly, otherwise weeds will become resistant. 

That is the message from the national Glyphosate Sustainability Working Group (GSWG).  Consisting of researchers and industry representatives and with support from CropLife Australia (formerly AVCARE) and the Australian Weed Management CRC, the GSWG has the task of minimising the development of glyphosate resistance and maximising the effective life of this key herbicide.

Since 1974, when glyphosate was first introduced, researchers have been searching for molecules with similar properties.  Every year, the major crop protection companies involved in research and development each screen approximately 0.5 million compounds in the hope of identifying potential new pesticides.

Based on the low number of products with unique characteristics released in recent years, it can be deduced that not many unique molecules or compounds with all the attributes of crop safety, efficacy, environmental and human safety are found.  Of those found, not all are suited to Australian weeds or our broadacre crop production.

Currently there is no glyphosate equivalent in development, so growers must use glyphosate responsibly to prevent the development of glyphosate resistant weeds, especially annual ryegrass, on their property.

Responsible use includes diversifying the range of herbicides applied as well as using physical rather than chemical control methods to reduce weed seed banks.

The strategic use of alternative ‘knockdown’ herbicide groups, that are not Group M, effective in-crop weed control, use of alternative herbicide groups or tillage for inter-row or fallow weed control, crop topping using weed seed catchers at harvest and using the ‘double knock’, are all alternatives that can help lower the risk of herbicide resistance.

The ‘double knock’ is an application of glyphosate followed by application of a paraquat-based product.  This strategy relies on paraquat controlling rare glyphosate resistant survivors.  The glyphosate survivors are not often controlled by low rates of paraquat, nor are large ryegrass plants. so the ‘double knock’ strategy relies on applying both herbicides at appropriate rates for the targeted ryegrass plants.

Assisted by the Australian Weed Management CRC the GSWG has developed a website (www.weeds.crc.org.au/glyphosate/) containing useful information and resources about weed management techniques to minimise the risk of glyphosate resistance.  There are answers to frequently asked questions, fact sheets, information on identification and testing for glyphosate resistance and a database of glyphosate resistant weed populations.  Growers and agronomists are encouraged to visit the site and use and share the information as widely as possible.

The Crop Doctor, Peter Reading, is managing director of the Grains Research and Development Corporation (GRDC), Canberra.