Grains Research and Development Corporation
The Crop Doctor - Focus on

The Macquarie Dictionary defines “precious”  as “of great worth and value”.  It gives a second meaning as “of great moral or spiritual worth”.

The University of Western Australia’s Professor Stephen Powles could have had both meanings in mind at the 4^th International Crop Science Congress in Brisbane, where he said modern herbicides were too precious to be allowed to fail because of resistant weeds.

“The technology that will dominate crop weed control in 2020 will be conventional and gene driven herbicides – modern, efficient, environmentally clean, selective herbicides,” Professor Powles said.

“But they are more than just another resource to be used by farmers. Glyphosate, which has allowed chemicals to be substituted for the plough on so much of Australia’s cropping land, is as valuable to farmers as antibiotics are to the wider community.”

Professor Powles, who is director of the Grains Research and Development Corporation (GRDC)  Herbicide Resistance Initiative in Western Australia, told his congress audience Australia had the world’s largest herbicide resistance problem.

Other parts of the world shared the Australian situation of farming systems and landscape with little diversity, large farms and strong reliance on zero tillage in broadacre farming, but not its widespread populations of annual ryegrass. 

“Sown and nurtured” over some 60 million hectares, ryegrass was an excellent pasture grass for livestock, but had emerged as a problem when farmers converted  much sheep country to cropping. 

Ryegrass in Australia had become the world’s most resistant weed species, because it was genetically diverse and present at huge numbers across vast areas, where it then was  persistently treated with herbicide in a system with little cropping diversity.

However, although multiple herbicide resistant ryegrass was widespread in southern Australia, farmers are doing a good job of managing this problem. 

Farmers had responded to emerging resistance with a number of non-herbicide strategies – doubling crop seeding rates to suppress weeds, windrowing and burning stubble, trailing  chaff carts behind the header to catch the weed seed, trailing hay balers behind harvesters and fitting harvesters with extra sieves to capture ryegrass seed.

There was even an experimental mill –  to grind up weed seeds – being tested on some harvesters.

Professor Powles emphasised the need for more diversity in the system, including phase pastures in their rotations,  two or three years of species like serradella before returning paddocks to crop.

This enabled elimination of weed seed production during the pasture phase, ensuring the farmer commenced a subsequent lengthy cropping phase with very low weed seedbanks in the soil

“However resistance management has to stay profitable and farmers are mainly tackling herbicide resistance with the herbicides that still work,” Professor Powles said. 

“There is massive reliance on glyphosate and trifluralin, especially in no till farming systems.  These herbicides must be preserved and one way to help ensure this is to diversify herbicide use by rotating with other herbicide groups

“For example, rotating to paraquat is a way to help ensure the longevity of glyphosate. We’ve been encouraging growers to practise herbicide diversity.”

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