New glyphosate resistant liverseed grass population confirmed in northern NSW

Author: Andrew Storrie | Date: 22 Jan 2014

Three samples of liverseed grass. The new Gunnedah population on the left looks healthy, showing it has a much higher level of resistance compared to the sample in the centre which is known to be susceptible, and the original resistant Moree population on the right.

The world’s third case of glyphosate resistant liverseed grass has been confirmed in northern New South Wales, seven years after the first two cases were confirmed from east of Moree. The latest infestation comes from a mixed cropping farm near Gunnedah and adds to the concern of almost 100 confirmed cases of glyphosate resistant barnyard grass populations in this region.

“While this is only the third confirmed case of glyphosate resistant liverseed grass in seven years, it comes from a new area and has a much higher level of resistance than previous populations,” stated Tony Cook, Technical Specialist (Weeds) with NSW Department of Primary Industries. “This population is widespread on the farm in question, but like most summer grasses occurs in patches.”

The farmer suspected he had a problem about three years ago, but has been able to control it in cotton with Group A selective grass herbicides. His main worry has been that it was on the irrigation head ditches where the seed could spread across his irrigation. Also being on a flood plain, he is worried about weed spread between farms.

The farm is on the Liverpool Plains, an area made famous in 1998 with the discovery of the first broadacre cases of glyphosate resistant annual ryegrass.

“Glyphosate resistant ryegrass is found all across the southern sections of the Liverpool Plains and farmers are managing to live with it,” says Mr Cook. “The problem is summer grasses are usually harder to control due to heat and moisture stress and the short time needed to set viable seed, so you really need to be on the ball with your spraying operations.

“We are going to sit down with the farmer and his agronomist to develop an integrated weed management plan to get on top of the liverseed grass. This will also assist in preventing the same thing happening with barnyard grass, which is a much tougher weed problem.”

One thing in the favour of farmers managing liverseed grass is that over 95 per cent germinates in one flush in mid spring, which is probably a major reason it has taken seven years to find another population. Barnyard grass on the other hand will germinate from September to April, making control on-going and extremely difficult.

“The advantage Liverpool Plains farmers have is quite a few rotational options that allow switching between winter and summer fallows and using broadleaf summer crop like sunflowers and mung beans, which in turn allows different planting times and use of a range herbicide modes-of-action. Planting these after the main liverseed germination flush in October allows you to control summer grasses with paraquat and pre-emergent herbicides before sowing. Any escapes can be controlled with selective grass herbicides in-crop.”

Imazapic can be used in summer fallow as a residual herbicide to control multiple weed germinations and then be followed by a winter crop of chickpeas or imidazolinone-tolerant barley.

“Farm hygiene controlling weeds around irrigation structures, buildings, fences and roads will be a critical part of the overall plan,” stressed Tony. “We can’t continue to rely on a few herbicides for weed control as this is a recipe for failure. Without looking at all facets of the farm operation and using non-herbicide strategies as well, you can’t keep the lid on herbicide resistance.”

Stopping seed set is the key to managing herbicide resistance; however this needs determination and an eye for detail.

If you suspect glyphosate resistant liverseed grass or barnyard grass on your farm phone Tony Cook at Tamworth on 0447 651 607.

For more information on managing glyphosate and paraquat resistance visit the AGSWG web site

For information on herbicide sustainability visit the WeedSmart information hub at


Photo Caption:  The new Gunnedah population (left), showing it has a much higher level of resistance compared to known susceptible (centre), and original resistant Moree population. Plants sprayed with 1.6 L/ha glyphosate (450 g/L).


Tony Cook
NSW Department of Primary Industries
(02) 6763-1250
0447 651 607

GRDC Project Code UQ00062; UA00124; ARN00001

Region North