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App helps mungbean growers manage powdery mildew

Left to right: A mungbean plot sprayed with a fungicide and a control plot from the same replicated trial.
Photo: Kirsty Owen, University of Southern Queensland

Key points

  • The PowderyMildewMBM app helps growers decide how to best manage mungbean powdery mildew.
  • The app uses data from 16 disease management trials carried out in Queensland and New South Wales from 2011 to 2019.
  • Calculations and management decisions have been further validated in trials since 2022.
  • The app is free and available from both Google Play and Apple App Store.

The PowderyMildewMBM app has been helping mungbean growers across Queensland and New South Wales better manage powdery mildew.

It uses powdery mildew severity and grain yield data obtained from 16 disease management trials carried out in Queensland and New South Wales from 2011 to 2019, enabling growers to calculate estimates of financial return from each planned spray.

The app calculates based on:

  • application costs and expected efficacy (depending, for example, on aerial or ground sprays)
  • expected yields and grain price
  • crop stage
  • weather forecast.

The app allows users to run different scenarios for any paddock and compares the expected monetary returns for one or two sprays, or no spray at all. It supports the principle “if it doesn’t pay, don’t spray”.

App-based decisions validated in trials

From 2022 onwards, seven trials were run in Queensland to further validate the app based on disease incidence, severity, and yield data.

In addition to these replicated validation trials, six demonstration areas were set up in mungbean paddocks managed by agronomists and growers who have engaged with the project. These 100-200 m2 areas were clearly marked up and were only sprayed if the PowderyMildewMBM app predicted financial gain from fungicide applications.

The rest of the paddocks were treated as per the managing agronomist’s practice. Powdery mildew incidence and severity were regularly monitored in both parts of the paddocks, i.e. the demonstration areas and the rest of the crop.

All six demonstration sites supported the decision support tool’s predictions. In five of the six sites, these matched the agronomists’ disease management decisions. Two cases are presented below.

Case study 1

In a paddock planted on 50cm row spacing in the first week of September 2022, much earlier than the usual mungbean growing season, powdery mildew was not detected at any time during the crop growth. However, at flowering, a preventive spray of Tebuconazole was applied by the grower “for peace of mind”.

In the absence of the disease, the PowderyMildewMBM app did not recommend fungicide treatment, therefore the demonstration area was left unsprayed.

By estimating the spray cost at $15/ha, no rain forecast in the next seven days, and an average maximum temperature of 29°C, the PowderyMildewMBM app calculated a risk of a negative net return (-$9/ha) if the paddock was sprayed once (see image).

In that year, in-crop rainfall was much lower than the long-term average (153mm from September to January compared to 329mm) and mean monthly temperatures were similar to the long-term average (range of 22 to 37°C).

Powdery mildew was not present at harvest, neither in the demonstration area or in the rest of the paddock.

The preventive spray was proven unnecessary.

Table 1

In Case Study 1 a screenshot from the PowderyMildewMBM app shows that there was a predicted negative net return by spraying Tebuconazole at flowering with no rain and a maximum temperature of 29°C forecast over the next seven days.

Case study 2

In a paddock planted the last week of December 2021 on 50cm row spacing, powdery mildew first appeared in early March 2022 at the green pod stage. The disease was found in the lower third of the canopy with up to 75 per cent of plants affected but with small colonies covering only 10 per cent of the leaf area.

The PowderyMildewMBM app predicted a net return of $27/ha from one spray, with a seven-day forecast of one rainfall event and the average maximum temperature of 26°C. The predicted net gain decreased to $12/ha if fungicide was applied twice.

The managing agronomist immediately sprayed the paddock and the demonstration area against the disease. The disease was very well controlled, and 11 days later there was a very low level of powdery mildew with only occasional spots of infection in the lower third of the canopy detected. A second spray was not applied and, in the week before harvest, no powdery mildew was detected.

Table 2

The PowderyMildewMBM app produces a report which can be saved or directly emailed. In Case Study 2, the app predicted a mean net return of $27/ha for one spray at the green pod stage with one rainfall event and a maximum temperature of 26°C forecast over the next 7 days.

In that season, the in-crop rainfall was much greater than average (520mm compared to the long-term average of 240mm) and mean monthly temperatures were similar to the long-term average. Despite these wet conditions, the effective and immediate control of powdery mildew with one spray paid off.

The PowderyMildewMBM app predictions were supported by these results.

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