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Herbicide resistant weeds: Southland

Published on 09/06/2022

A team from FAR and AgResearch visited 27arable farms, pre-harvest, to collect weed seeds as part of FAR’s herbicide resistance project within the AgResearch-led MBIE Weeds Programme. The seeds were then sent to AgResearch’s Hamilton facility for resistance testing.
FAR senior field officer, Ben Harvey, says
seed from suspected herbicide-resistant weeds is tested by growing it out then spraying with herbicides at label rates. When more than 10 per cent of plants survive an application, they are classed as resistant.

“Testing has now been completed on the
grass weed seed portion of the samples collected. Over 250 individual tests were carried out on plants, which represented five different genera.

“In all, eight of the 27 farms tested had
some form of herbicide resistant weed present, with 5 per cent of all tests returning a ‘resistant’ result.

“The most common resistant weed genus
was Poa, which exhibited resistance to iodosulfuron. Other resistant weeds were wild oats (resistant to fenoxaprop) and ryegrasses (resistant to haloxyfop, iodosulfuron orpyroxsulam).

“All herbicide resistance in grass weeds de
tected in these surveys to date has been to active ingredients in Groups 1(A) or 2(B).

Work is ongoing at FAR and elsewhere to
identify alternatives to these herbicides, to ensure that weed management tools remain available to growers in the future, Harvey says.

The programme is also continuing to sur
vey other areas of New Zealand. In 2022, the team is surveying arable farms in Manawatu, Wairarapa and Hawke’s Bay.

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