Grains Research and Development

Date: 04.05.2015

Feathertop Rhodes grass becoming a nuisance down south

Author: Elisabeth Berry

Feathertop Rhodes grass is a common weed in the northern grains region, but it is now also emerging as a problem for growers further south

Image of Feathertop Rhodes grass

Feathertop Rhodes grass in paddock margins, Biloela, Central Queensland.

PHOTO: Tom Dixon

The need to assist northern growers and their advisers in combating feathertop Rhodes grass (FTR) has led to the publication of a new integrated weed management manual on the weed – an initiative of the GRDC’s Central Queensland Grower Solutions (CQGS) group and co-funded by the GRDC and the Queensland Department of Agriculture and Fisheries (DAF).

Once common only on roadsides and fencelines, FTR is now more widespread due to the shift in cropping systems to minimum or zero-tillage, as has been the case with many emerging problem weeds in non-traditional areas.

Image of Darren Aisthorpe

Queensland DAF researcher Darren Aisthorpe inspects a patch of resistant feathertop Rhodes grass in a paddock at Biloela, Central Queensland.

PHOTO: Tom Dixon

“FTR is now a formidable challenge to current zero-till farming systems across Queensland and New South Wales,” says CQGS extension agronomist Darren Aisthorpe, from Queensland DAF.

A reliance on knockdown herbicides (glyphosate) has failed to manage the weed. Field observations show that since 2011 the efficacy of glyphosate on FTR has continued to decline.

“For many growers the battle against FTR has long been fought with knockdown herbicides and slowly but surely that battle is being lost,” Mr Aisthorpe says.

The threat of resistance and selection for increased tolerance in weed species means that knockdown herbicides can no longer be automatically considered the preferred option for grass weed management. Weeds such as FTR now require a much broader suite of strategies, used in combination, to help slow the inevitable transition to the weed becoming herbicide tolerant.

“What we need to consider is giving up our reliance on ineffective knockdown strategies and moving instead to a multi-pronged strategy that helps stop seed-set and exhausts the seedbank,” Mr Aisthorpe says.

Knowing the enemy

FTR (Chloris virgata Sw.), also known as Feathertop Chloris, hairy Rhodes grass and woolly-top Rhodes grass, is a native of North America. It is a tufted annual grass that grows up to one metre tall and produces large plants on a shallow root system.

FTR establishes fast in lighter-textured soils and is capable of producing up to 6000 seeds per plant. The flower and seed heads have feathery spikes, with the feathery appearance coming from the stiff white hairs and awns arising from the seeds.

FTR is often the first species to germinate after rainfall, and the plants stress easily and quickly (often before other species in the paddock), making herbicide uptake difficult. However, FTR seed is relatively short-lived, so if seed production can be stopped for 12 months the seedbank can be exhausted relatively quickly.

“The FTR seedbank can be fully depleted in 12 to 18 months, so with a careful use of weed-seed control, crop rotation, strategic tillage and techniques such as burning on top of traditional herbicide control, growers stand a good chance of being able to remove the weed successfully,” Mr Aisthorpe says. 

“FTR can certainly withstand many individual weed-control methods, but through a well-planned weed-management strategy it can be targeted effectively,” Mr Aisthorpe says. “This is what the new manual aims to help growers achieve in the northern region.”

A strategy guide

The new FTR manual offers an overview of FTR and its biology as well as practical advice on all aspects of FTR management. Recommendations are based on the latest FTR research findings on:

  • herbicide efficacy;
  • effects of strategic tillage on seed placement in the soil profile;
  • seedbank viability at differing burial depths;
  • the effect of different implements on FTR emergence; and
  • the impact of crop rotation on FTR management.

The manual suggests control tactics, post-emergent and residual herbicide options and the use of crop rotations. It offers advice on chemical groups to include in a management program and implementation of an effective integrated control strategy.

“Growers, for instance, can use simple techniques such as broadleaf crops in rotation with cereals to broaden the residual control and knockdown options,” Mr Aisthorpe says. “More fundamental ideas, like using narrow rows and uniform plant populations, will also increase crop competitiveness.”

FTR management case study

Moonie, Queensland, grower Neville Boland, who cultivates about 4000 hectares a year near Goondiwindi, says the advent of herbicide resistance in weeds – in particular flaxleaf fleabane, FTR and barnyard grass – has affected his crop rotation and soil management.

“There’s a lot of FTR around our property,” he says. “It’s been growing around here for some time. I remember seeing it in the 1980s around the old oil well sites and gravel roads on my dad’s place. It’s really strange that it’s now growing everywhere, including in my lawn. I think it’s here to stay, but that doesn’t mean it can’t be controlled.”

Mr Boland says he used to have a flexible rotation or an opportunity cropping system, but with the advent of weed resistance and FTR he has had to turn to more residual herbicides. “But that’s restricting our opportunity cropping a little bit and it’s making fallow management quite a bit harder.”

To recover from this situation, Mr Boland introduced strategic tillage into his farming system.

“If you use a careful, minimum tillage and don’t bash the soils about it is possible to manage FTR,” he says. “Tillage is certainly a lot cheaper and it gives you more robust control. We till, for instance, when there’s no stubble; we do it in one pass using rotary harrows behind a cultivator. This keeps the operation one-pass rather than needing a second pass to sort out lumps and clods left by finger harrows.

“With sodic soils like we have here, gypsum combined with zero-tillage can be used as a kickstarter to encourage better infiltration and therefore improve the soil.

“By thinking strategically, I’ve managed to control my FTR problem.”

More information:

Darren Aisthorpe
0427 015 600

darren.aisthorpe@daf.qld.gov.au

End of Ground Cover issue 116 northern edition

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