THE world's third case of glyphosate resistant liverseed grass has been confirmed in northern NSW.
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The finding comes seven years after the first two cases were confirmed from east of Moree.
A statement released by Grains Research and Development Corporation (GRDC) said the latest infestation comes from a mixed cropping farm near Gunnedah, adding to the concern of almost 100 confirmed cases of glyphosate resistant barnyard grass populations in the region.
NSW Department of Primary Industries technical specialist (weeds), Tony Cook, said while it was only the third confirmed case of glyphosate resistant liverseed grass in seven years, it was from a new area and had a much higher level of resistance than previous populations.
"This population is widespread on the farm in question, but like most summer grasses occurs in patches," Mr Cook said.
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, where in 1998 the first broadacre cases of glyphosate resistant annual ryegrass were discovered.
"Glyphosate resistant ryegrass is found all across the southern sections of the Liver-pool Plains and farmers are managing to live with it," Mr Cook said.
"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."
More than 95 per cent of liverseed grass 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 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," Mr Cook said.
"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."
GRDC reports 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.
If you suspect glyphosate resistant liverseed grass or barnyard grass on your farm contact Tony Cook at Tamworth on 0447 651 607.
