Herbicide-tolerant lentils: Registration and impacts

Lentils are becoming easier to integrate into dryland cropping rotations with the development of herbicide tolerance traits. GRDC investment is generating data to support APVMA permits and label registration for these novel herbicide-use patterns.

With limited in-crop herbicides for use on pulse crops, GRDC investment has been supporting breeders in developing herbicide tolerance traits in lentils.

These traits have been achieved using conventional breeding strategies, avoiding the potential issues that arise with the use of GMO technologies.

The herbicide tolerance traits allow for novel herbicide uses that require new registrations to be approved by the Australian Pesticides and Veterinary Medicines Authority (APVMA). To facilitate these registrations, GRDC invests in crop safety, efficacy and grain residue field studies. In partnership with industry, GRDC helps develop the required registration data packages.

The manager for chemical regulation at GRDC is Gordon Cumming. He oversees GRDC efforts to help secure access for Australian growers to chemical crop protection products overall. This is especially important for industry sectors that are not financially attractive to commercial companies, such as the smaller specialty crops including pulses and some oilseeds.

″The regulatory process is a critical component of releasing these new herbicide tolerance traits and ensures registered herbicide labels are available to support appropriate and effective use of these chemistries,″ Mr Cumming says. ″Initially, before full label registration, a minor use permit may be sought.″

Herbicide-tolerant lentil permits

The first APVMA minor use permit was obtained for imidazolinone-tolerant lentils. The subsequent label registration was achieved in partnership with NuFarm for Intercept^® herbicide. Current varieties with this tolerance include PBA Hurricane, PBA Hallmark XT, PBA HighlandXT, GIA Lightning and GIA Thunder.

To maximise agronomic benefits and suppress the emergence of resistant weeds, herbicide tolerance technology is being developed targeting different chemistries and modes of action, including metribuzin.

Such herbicides would allow for early post-emergence weed control targeting broadleaf weeds and, in the case of metribuzin, brome and annual ryegrass. This would bring significant agronomic benefits.

A range of herbicide tolerance traits provides broader herbicide choice and more-effective weed control.

″It also puts different chemical modes of action into play for more sustainable and integrated forms of weed control,″ Mr Cumming says.

APVMA minor use permit PER92810 was obtained in 2023, allowing for the early post-emergent application of metribuzin to new tolerant lentil varieties including GIA Metro. Preparations to obtain label registration are underway.

A key consideration in the regulatory process is the risk to trade that detectable herbicide residues may present. These herbicide tolerance technologies are uniquely Australian and as such there are no maximum residue limits (MRLs) set in export markets.

If there are no herbicide residues detected in the grain, then there is a clear pathway to registration. This is the case for metribuzin-tolerant lentils. However, for some other herbicide types, detectable residues are present in the grain, which becomes a significant barrier to registration.

″The main issue is that lentils are primarily exported and as part of the registration process, the APVMA must consider if detectable residues are likely to represent an unacceptable risk to trade and acceptance by the end-user,″ Mr Cumming says.

″Efforts are underway to discuss the situation with exporters and marketers regarding the mitigation of potential market risks.″

Demonstrating weed control with the inclusion of metribuzin in GIA Metro lentils. Photo: Janine Souness, PB Seeds

Pathway to market

Mallee grower Kate Wilson, a trained agronomist, was a strong advocate for a GRDC role in pursuing minor use permits for herbicide-tolerant (HT) lentils. As a Southern Panel member, she contributed and assisted in establishing the partnership with NuFarm.

″We had a situation where we were backing the breeding of herbicide tolerance traits but there was no path to market since the chemical companies would not undertake the required registrations,″ Ms Wilson says.

″When GRDC stepped up, it was a game changer for growers. Lentils can change the economics of a farming system and when GRDC invested in the registration process, they created a pipeline that puts lentil cropping in reach of an expanding group of farming systems.″

Ms Wilson and her husband, Grant, use HT lentils in their broadacre grain production business in a low-rainfall, high-risk environment. She says lentils bring the benefit of a break crop combined with a reliable positive cash flow.

This profitability can prove essential in environments where one year in four can be a wipe-out.

Herbicide tolerance has expanded lentil cropping enormously.

″In the early days, it was the ability to use herbicide over the top that made the difference,″ Ms Wilson says. ″It brought weeds such as radish under control, making it possible to get the yields and grain quality growers needed.″

She adds that more and more farming systems can benefit on the back of additional traits and registrations. Collectively, these changes are making lentils an integral part of southern rotations and the component that can earn the highest financial return.

″With herbicide tolerance traits, the more bullets in the gun the better, as each chemical group helps make lentil production more sustainable,″ she says.

On-farm impacts in Victoria

In Victoria’s Mallee, agronomist Andrew McMahen of Nutrien Ag Solutions says the region’s high level of lentil production relies entirely on imidazolinone-tolerant varieties.

Imidazolinone-resistant milk thistle. 

This tolerance also allows lentil crops to cope with soil residues from the cereal parts of the rotation. That means each tolerance trait helps retain a herbicide for use on crops grown prior to the lentil phase.

″Some herbicides can take a long time to break down due to the region’s sandy soils and low rainfall,″ Mr McMahen explains. ″While lupins and vetch can tolerate some residues, lentils cannot.

Genetic tolerance to key herbicides, therefore, would allow for important innovations to weed management more broadly. It helps make lentils a better fit into these farming systems while allowing growers the use of herbicides that provide cost-effective control options to important weeds, such as milk thistle.″

Uptake of the imidazolinone-tolerant varieties, however, depends on breeders also bringing in the high-yielding genetics. This is proving true with the metribuzin tolerance trait too.

″Lentil cultivars with metribuzin tolerance have been released, but the yields are not there yet,″ Mr McMahen says. ″Yields need to match those possible with the imidazolinone-tolerant varieties before we will see widespread uptake.″

He adds that while lentils were first included in these farming systems as a break crop, they are now considered a cornerstone of profitability in southern farming systems as they can be the highest-income crop in the rotation.

Mr McMahen reports lentil crops in 2022 achieved yields of 2.5 to 3.5 tonnes per hectare. Commodity prices in late 2023 were about $900/t. But even in 2022, when the price was closer to $500/t, growers found that lentils stored well, which allowed for strategic selling at prices between $800 to $1000/t depending on the grain’s grade.

Some growers were also able to overcome the season’s wet finish and upgrade the price fetched on stored grain by using a grain cleaning service at about $30/t to remove wrinkled grain or vetch and medic contamination.

On-farm impacts in SA

Agronomist Martyn Chandler of Cummins Ag Services is based in Cummins on the lower Eyre Peninsula. He says the Yorke Peninsula has led the way initially in the adoption of lentils and, more recently, HT lentils.

The first HT variety – released in 2011 – was PBA Herald XT followed by PBA Hurricane XT. Recently, there has been a significant improvement in yield potential with the release of imidazolinone-tolerant GIA Thunder, which is now the dominant variety.

Prior to the release of the first imidazolinone-tolerant lentils, wick wiping was required to prevent ‘blow-outs’ in brassicas and thistles. Bedstraw control was limited and controlling bifora medic and vetch in-crop was impossible.

The imidazolinone herbicides, along with imidazolinone-tolerant lentils, were initially successful at controlling brassicas, medics, vetch, bifora and bedstraw and, to some extent, milk thistle.

″This early period in the uptake of imidazolinone lentils saw wick wipers being phased out as the imidazolinone herbicides offered control of these troublesome weeds,″ Mr Chandler says.

Without imidazolinone herbicides, the infrastructure and significant costs associated with cleaning lentils of weed contaminants was needed to ensure lentils could be delivered to market.

Resistance

With more than a decade of use, an important trend is the appearance of resistance to imidazolinone (Group 2) chemistry in brassicas, thistles, bedstraw and bifora.

Imidazolinone-tolerant (Group 2) prickly lettuce. Metribuzin-tolerant lentils are a strong option to control this weed. Photo: Central Ag Solutions

A further issue with imidazolinone herbicide use is its long soil persistence. This often requires the following year’s crop to be an imidazolinone-tolerant cereal or canola, which limits variety choice and introduces further weeds into the canola phase.

It is these complications that make the arrival of GIA Metro so important. It is the first dual metribuzin and imidazolinone-tolerant lentil variety. With this variety being the first-generation release, it has demonstrated lower yields than the currently grown herbicide-tolerant lentils in ‘weed-free’ trials.

However, Mr Chandler says there is caveat. ″Caution is required when growing current imidazolinone-tolerant lentils and using Group 5 (triazine and urea) herbicides,″ he says. ″It is a catch 22 situation. Low rates help crop safety but provide inferior weed control. High rates increase weed control but often damage crops. This damage in turn allows more weeds into the crop as crop competition is reduced. So, in the field, when comparing GIA Metro to GIA Lightning/Thunder, the yield gap is often a lot closer.″

Weed control

″For many lentil growers, metribuzin tolerance offers superior levels of weed control across all the problematic weeds without damaging the crop or posing plant-back challenges for next year’s crops.″

In the eastern and western Eyre Peninsula, Mr Chandler has seen growers realise the benefit lentils provide with an estimated jump to 145,000 hectares planted for 2024 in this region.

″In this mid to lower-rainfall region, medic is a major issue,″ he says. ″While the Group 2 herbicides offer some means of control, the chemistry is very persistent given lower rainfall and light alkaline soils. Also, the imidazolinone-tolerant medic species Seraph and Angel are not controlled with imidazolinone herbicides.″

In general, contamination by vetch (particularly woolly pod types) still poses a major challenge. Mr Chandler sees the need for additional chemistry groups.

Overall, he thinks growers are keen to realise the gains possible from having a mix of chemistry available in HT lentils. However, for this to occur, continued action on registration is required.

″Support that the GRDC provides with chemical regulation is important to the success of lentil producers,″ Mr Chandler says. ″This support with registration in turn incentivises breeding companies to continue to invest in variety improvements.″