Three new videos from the Australian Fungicide Resistance Extension Network (AFREN) will help southern region growers improve their fungicide and fungal disease management.
With a range of factors driving high global demand and prices for grain, any yield losses caused by avoidable fungal disease could have an outsized effect on harvest earnings.
The new videos offer valuable advice on applying fungicide strategically to minimise risk and maximise economic returns, managing fungicide resistance risks in canola, and grower management to prevent fungicide resistance in the medium-rainfall zone.
Fungicides are incredibly valuable tools for protecting yields. However, they are also surprisingly vulnerable and must be used carefully to avoid the development of fungicide resistance.
The AFREN project has been a significant three-year GRDC investment to improve awareness of fungicide resistance risks and best practice fungicide usage. Bringing together plant pathologists, fungicide resistance researchers and extension specialists from across the country, AFREN has published a wide range of informative videos, podcasts, webinars, fact sheets and guides via its website.
Research scientist Tara Garrard from the South Australian Research and Development Institute, the research division of South Australia’s Department of Primary Industries and Resources (PIRSA-SARDI), presents the new grower management video. She says fungicide resistance is driven by a combination of high disease pressure and poor fungicide management.
“The main factors encouraging disease in the southern growing region are growers planting susceptible or very susceptible varieties and reducing rotation in their cropping program,” she says.
“In South Australia, we’ve seen problems like SDHI-resistant net form net blotch emerge in barley because of these practices in combination with repeated use of a vulnerable fungicide group.
“We have also seen the emergence of wheat powdery mildew with resistance to Group 11 strobilurins.
“These resistant pathogens have spread and emerged independently in different areas.”
To avoid favouring resistant pathogen strains within a field population, fungicides should always be used in rotation so that no single product or chemical active is applied twice in succession.
Spraying wheat for powdery mildew near York in Western Australia. Photo: Evan Collis
Using fungicide actives in mixture can help reduce the risk of resistant pathogens surviving a treatment, although it might also increase the rate at which you go through available options. Several popular actives should not be used more than twice in the same season, alone or in mixture, due to existing resistance risks.
Growers must check fungicide labels for mandated usage conditions. Further guidance is available on the AFREN and CropLife Australia websites.
Dr Garrard says all fungicide use should be carefully planned and recorded, including seed treatments and in-furrow applications, to help avoid use of the same fungicide twice in succession.
“Plan your fungicide program for the paddock, not the disease,” she says. “For example, a wheat paddock with a mild rust problem could still have a powdery mildew population as well.”
“So when you treat the rust with a fungicide, the powdery mildew gets a shot of it at the same time, which favours any resistant individuals within that population.
“Treating a subsequent powdery mildew outbreak in the same paddock with the same fungicide can further encourage the resistance development.”
Recent La Nina and negative Indian Ocean Dipole conditions have fuelled the prospect of a bumper harvest this year. However, wetter summers have also delivered a prolific ‘green bridge’ supporting seasonal disease carryover in many crops. Any prolonged wet periods will intensify the disease pressure as canopies close.
Disease inspection
Regular inspections are the foundation of good fungicide management.
Simply spraying on a schedule, whether disease is present or not, has the potential to use up the limited number of fungicide ‘shots’ that can be safely applied each year and may necessitate high-risk practices if there is an outbreak later in the season.
It is far better to wait and spray when there is clear evidence of disease.
Even then, most foliar diseases of cereals can only cause yield loss if they infect the top three leaves of the plant. Disease inspection and fungicide decisions should focus on these ‘money leaves’. Keeping them green and disease free will ensure the plant can capture the sunlight it needs for optimum grain fill, even if the lower leaves have a visible infection.
“Try to plan and manage your fungicide for the whole season,” Dr Garrard says.
“Using fungicides in mixture and rotation will help you avoid encouraging resistance, while only spraying when disease is a problem on those top three leaves will help you have options if weather conditions lead to a late disease outbreak.”
Pulse crop diseases have remained almost completely free of fungicide resistance in Australia to date. However, isolated examples of resistance in Ascochyta blight of lentils and Botrytis grey mould have been reported here and overseas, making the need to practise careful fungicide management in pulses no less essential.
Blackleg of canola is a significantly different case due to the way infection can affect a crop. For in-season advice on when spraying for blackleg will deliver an economic return, canola growers should refer to the BlacklegCM blackleg management app.
Agronomy the key to management
Regardless of the crop, however, Dr Garrard says using agronomy to reduce disease risk and in-crop pressure is crucial to good fungicide management.
“It takes a year-round approach,” she says. “After harvest, minimise the inoculum left in the paddock by managing stubble loads and planning the next year’s rotations to maintain time and distance between plantings.
“Anticipate local disease risks based on experience and seasonal weather forecasts, then avoid planting susceptible or very susceptible cultivars.”
The threat of fungicide-resistant crop diseases highlights the importance of year-round integrated disease management (IDM) practices to minimise disease pressure and in-season reliance on fungicide applications.
Even early in the winter crop growing season, most growers will have played all the agronomic cards in their IDM strategy, leaving fungicide application as their remaining disease control tactic.
Being strategic about the timing and rotation of those fungicide applications can help minimise input costs and support profits. It will also ensure that current fungicide chemistries can continue to protect yields at critical moments in this and future seasons.