Pre-emergent herbicides part of the FTR arsenal

GroundCover Live and online, stay up to date with daily grains industry news online, click here to read more
Feathertop Rhodes grass

Feathertop Rhodes grass has a short seed life, so focused control measures over two years could bring the weed in check.

PHOTO: Econnect

Pre-emergent herbicides have a role to play as part of an integrated weed management (IWM) strategy to control feathertop Rhodes grass (FTR), but they are not a standalone solution.

This is the latest advice from Richard Daniel from the Northern Grower Alliance after ongoing GRDC-supported trials into management tactics for the rapidly escalating problem of FTR.

Crop rotation, strategic and salvage tillage, intensive patch management (for new incursions) and salvage burning with a range of both residual and knockdown strategies were critical to successfully manage FTR, along with weeds such as fleabane and awnless barnyard grass.

“Our management issues with FTR have in part stemmed from an over-reliance on glyphosate,” Mr Daniel says.

“It was always expected that as our reliance on knockdown herbicides increased – both in-fallow and in-crop – there would come a time when growers would need to apply a more IWM strategy.”

The challenges of FTR control are compounded by the fact that glyphosate, even in a double-knock when followed by paraquat, rarely provides effective control. The weed is also quick to colonise bare areas (faster than awnless barnyard grass, fleabane or sowthistle) and can germinate on just 10 millimetres of rain.

Minimum and zero-till practices have also increased the FTR threat as the weed prefers to germinate on the soil surface and trials show negligible emergence at two centimetres or deeper.

So while residual herbicides are far from the solution, Mr Daniel says, they are one of the critical tools in controlling a range of weed species, including FTR.

Residual herbicides pre-crop or in fallow

Portrait of researcher Richard Daniel

Researcher Richard Daniel believes an integrated weed management approach is critical for the control of feathertop Rhodes grass.

PHOTO: GRDC

Using a residual herbicide in a fallow situation would seem logical, as it should maximise the amount of herbicide present when weeds are most likely to be active.

But Mr Daniel says the downside is limited crop competition to assist with weed suppression and a varied response across soil types and conditions, such as stubble levels or timing and quantity of rainfall. There is only one registered fallow residual herbicide option, Balance®, but additional product registrations are being sought.

Residual herbicides for FTR non-crop areas

FTR frequently dominates in non-crop areas, increasing the risk of re-infestation in crop. Imazapyr-based herbicides (for example, Arsenal®, Arsenal® Xpress) are registered for non-crop areas.

Residual herbicide in-crop advantages

Using residual herbicides in-crop opens the way for growers to implement other IWM approaches on-farm. In-crop use benefits from:

  • crop competition;
  • change in crop being grown;
  • more effective application conditions than in fallow, or with a level of mechanical incorporation; and
  • ‘increased disturbance’ planting may provide benefits with FTR control via weed seed burial or removal of early weed emergence.

“Currently there are no registrations for FTR in-crop residual control, although there are a range of Group A herbicides with knockdown registrations for FTR control in summer crops such as cotton, mungbeans, soybeans, sunflowers and peanuts,” Mr Daniel says.

Residual herbicides for awnless barnyard grass (for example, Dual Gold®, Flame®, Treflan® and Stomp®) applied in a range of summer crops have reduced FTR emergence.

FTR is predominantly a summer weed, but it can emerge during winter cropping, particularly in warmer situations. For the past three seasons, registered winter crop residual herbicides have been assessed for their effectiveness in controlling early FTR, along with other summer grass weeds.

Residual herbicides for the control of a range of grass and broadleaf weeds (for example, Balance®, Treflan®, Stomp®, Sakura® and Terbyne®) applied in a range of winter crops also offer potential for assisting FTR management.

Integrated approach vital

While trial work is continuing into how to improve efficacy from at-planting residual herbicides, the message for growers and agronomists is to employ an integrated approach to weed control.

“With in-crop application there is the added benefit of crop competition, but there are several rotation crops in which Group A herbicides are registered to allow knock-down control of FTR escapees,” Mr Daniel says.

Other options for FTR management include:

  • salvage cultivation of mature plants and inter-row cultivation for crops such as sorghum when grown on wider rows;
  • patch cultivation on new incursions (including manual weeding and chipping)
  • residual herbicides applied to new patches;
  • control using herbicides permitted through optical sprayer permits or registrations;
  • strategic cultivation for seed burial; and
  • burning where blowouts have occurred in patches or larger areas.

The role for residual herbicides

An integrated approach to weed-management tactics is critical, Mr Daniel warns, if growers do not want to lose glyphosate completely.

“The key to problem weeds, such as FTR, is to focus on individual paddocks and adjust rotations to crops that suit environmental conditions, are economic to produce, and also enable the use of effective residual herbicides in the previous fallow or even in-crop,” he says.

“This is particularly relevant for FTR. The seedbank is only short-lived and two years of intensive management can ensure that paddocks return to full flexibility of rotational choice.”

More information:

Richard Daniel,
07 4639 5344
richard.daniel@nga.org.au

Feathertop Rhodes grass fact sheet


Integrated Weed Management Hub

Next:

Grazing stubble benefits sheep and next-season crops

Previous:

Stop the rot early intervention key to disease control

GRDC Project Code NGA00004

Region North