Key points

• Improved opportunities to control broadleaf weeds in pulses are being targeted in future herbicide tolerant varieties
• Anticipated lentil varieties are expected to combine tolerance to imidazolinone herbicides with either tolerance to metribuzin or to soil residues of clopyralid
• Herbicide-tolerant field peas and faba beans are also in development

As the range of herbicide options in pulses expands, crop safety and yield remain paramount.

Herbicide-tolerant varieties have been a game changer in how pulse crops are managed and tend to be the preferred option where broadleaf weeds are an issue.

In southern Australia, about 60 per cent of today’s lentil crops are imidazolinone (IMI)-tolerant varieties, with some areas – such as the Yorke Peninsula – being close to 100 per cent. PBA Bendoc, the first IMI-tolerant faba bean, has also had rapid uptake in some regions.

Several new IMI-tolerant varieties are expected to be released in coming seasons. However, conventional varieties such as PBA Jumbo2 and PBA Bolt still offer a five to 10 per cent yield advantage in weed-free situations.

Research into new novel herbicide tolerance traits in pulse crops will provide growers with improved weed management options.

To help ensure the practicality of new novel herbicide tolerance traits, GRDC invests in pulse agronomy through Agriculture Victoria and the South Australian Research and Development Institute (SARDI). In collaboration with local farming systems groups, potential tolerant varieties are evaluated and appropriate usage is demonstrated to growers ahead of commercial release.

Targeted value

Varieties with herbicide tolerance have proved invaluable in managing broadleaf weeds in lentil, faba bean and field pea crops.

In experiments in South Australia, registered IMI herbicides provided more-effective control of vetch, bifora, medic, wild radish, wild turnip, prickly lettuce and common sowthistle, compared to non-IMI herbicides in IMI-tolerant faba beans and lentils.

Improved broadleaf weed control with IMI herbicides was associated with a yield advantage of 23 to 48 per cent in lentils and 10 to 41 per cent in faba beans compared to conventional practices with non-IMI herbicides.

Similarly, in Victorian trials a conventional non-IMI herbicide strategy was able to reduce yield loss from vetch competition to 23 per cent, while a strategy incorporating the use of IMI chemistry over tolerant varieties was able to prevent yield loss. However, neither of these control strategies completely prevented vetch seed set.

New developments

Although the release date is unknown, new lentil varieties have been developed that combine tolerance to IMI herbicides with tolerance to either metribuzin or to soil residues of clopyralid.

The metribuzin tolerance trait in lentils allowed the use of this herbicide at its highest label rate in research trials with no resulting crop damage. Usage at this rate improved control of bifora, and IMI-resistant Indian hedge mustard, common sowthistle and prickly lettuce, when compared with metribuzin used at lower rates because of safety concerns in conventional lentils.

A new Kaspa-type field pea with improved tolerance to residual IMI and sulfonylurea herbicides is anticipated soon.

New faba bean germplasm has shown improved tolerance to label rates of metribuzin applied post-sowing pre-emergent when compared to PBA Samira in field trials near Horsham. This breeding line yields well in Victoria and South Australia and could provide improved crop safety to metribuzin when applied post-sowing pre-emergent across a range of soil types, as well as improved broadleaf weed control.

Tolerance traits are invaluable in managing weed populations in pulse crops. However, herbicide rotation remains important in limiting the development of resistant weeds and preserving the future value of tolerant varieties.

More information: Dr Penny Roberts, 0436 678 982, penny.roberts@sa.gov.au; Dr Jason Brand, 0409 357 076, jason.brand@agriculture.vic.gov.au