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The fungus forecast: protecting crops from attack

7 December 2010

Mathematical models help UK farmers counter threat to oilseed rape.

Many countries pursue food security by specialising their agricultural production toward crops that fulfil domestic needs or have high export value. In the UK more than 600,000 hectares (around 6% of the country's arable land) will be devoted in 2010 to growing oilseed rape which is used in a variety of vegetable and industrial oils and as a constituent of biofuel.

  The fungus forecast: protecting crops from attack.

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Controlling pests and diseases on such a mass produced crop is crucial to individual farmers and the UK economy. Just as weather forecasts are an essential part of daily life for people around the world, pest forecasts can make the difference between a wrecked harvest and a profitable one that uses the least amount of chemicals possible, saving time, money and reducing the crop's environmental footprint.

Scientists have been developing forecasts for two serious diseases of oilseed rape since the early 1990s. Based at Rothamsted Research (RRes), an Institute of BBSRC, researchers have constructed models to optimise control of the two main diseases of oilseed rape - the fungal pathogens light leaf spot (LLS) Pyrenopeziza brassicae and phoma stem canker (PSC) Leptosphaeria maculans - which can save tens of thousands of pounds for individual farmers and the UK economy millions each year.

Dr Neal Evans and Dr Sue Welham have been modelling and forecasting the incidence and severity of leaf spot outbreaks at Rothamsted since the mid 1990s. "We are trying to understand the interaction between the disease, the host plant and environmental parameters such as temperature and wetness," says Evans.

Predicting pest and disease outbreaks can bring significant benefits. Image: RRes

Predicting pest and disease outbreaks can bring significant benefits. Image: RRes

The power of prediction

Light leaf spot is problematic because it causes an invisible symptomless infection in the autumn that can kill the plant over winter or cause severe damage come spring. However, spraying a fungicide in autumn affords the best control of the disease, but how do farmers know if their plants are infected?

That's where the forecast comes in. It is based on the severity of infection the previous season (which gives a baseline of inoculum, or infection), summer temperature (hotter weather leads to decreased pathogen growth on crop debris), and winter rainfall (because spores are dispersed by rain-splash) (ref 1).

Farmers can then use the forecast to decide whether to spray or not depending on risk. If they don't need to, they save money, time and resources by not using chemicals which benefits the farmer's business and the environment.

Evans says that the forecast, originally funded by the Home Grown Cereals Authority (HGCA), is freely available and that farmers love it. "We have had a really good response from growers and their advisors over the years with many positive comments on the ease of use and usefulness of the forecasts."

The light leaf spot life-cycle. Image: RRes

The light leaf spot life-cycle. Image: RRes

"In terms of benefit to the industry, we calculated that if just an additional 5% of farmers got good LLS control instead of poor or no control on 500,000 hectares, based on an average loss of 0.5 tonnes per hectare an extra 12,500 tonnes of extra oilseed rape seed per year on average could be grown." (0.5 x 0.05 x 500000 = 12500)

"At the current price of £300 per tonne that is £3.75M per year. We've been running the forecast since 1996, so as a rough estimate our small research project has probably saved the industry more than £52.5M," says Evans.

Fungal foes

Phoma stem canker (PSC) is a different adversary but shares some aspects of its life-cycle. Unlike LLS, which is polycyclic and has continued spread of new spores and infections throughout a year, PSC is monocyclic so there is only one generation per season. Phoma spores are released from crop debris in the autumn which, like LLS, is dependent on summer temperature and rainfall.

Damage to winter oilseed rape caused by phoma stem canker

Damage to winter oilseed rape caused by phoma stem canker

However, the PSC infections can be seen in autumn as phoma leaf spots on leaves, and if more than 10% of plants in a crop are affected the 'spray threshold' has been crossed and fungicides should be used to control the disease. If infection grows from the leaf spots into the stem before winter, damaging stem cankers begin to develop during spring that, if severe enough, can prevent water uptake and kill the plant before harvest.

As part of a Defra-LINK funded PASSWORD project, Evans and colleague Dr Andreas Baierl have developed a model to predict the onset of the PSC epidemic, the date of canker onset in spring, and canker severity at harvest (ref 1). "We now have an online system to provide information to farmers and advisors as to when to expect 10% phoma leaf spotting in the autumn, since this is the key threshold with respect to when best to target the disease with a fungicide," says Evans. "Part of the remit was to reduce reliance on 'calendar spraying' so that farmers only treat in high risk years, as in the case of the LLS forecast, and treat at the most effective time as in the case of PSC."

Media mashup

Evans is also using novel methods to communicate the forecasts, such as a Twitter account to disseminate updates, although he says that the website invites users to sign up and email is his preferred method. Evans has also used Google Maps, which uses its user-friendly map interface to display which areas of the UK will be above the 10% threshold. "I just did it manually in Google Maps, but you can do something more elaborate which is database driven," says Evans. "We use a similar approach in my current project ENDURE."

Forecast data combined with user-friendly programs effectively disseminates data. Image: Google Maps

Forecast data combined with user-friendly programs effectively disseminates data. Image: Google Maps

The ENDURE Virtual Laboratory (VL), also based at Rothamsted, aims to aggregate information on all aspects of crop protection research across Europe and beyond to facilitate research across disciplines and borders.

The advantage of using graphics-based applications such as Google Maps with database programs in a combination or 'mashup' is that the data can be merged and visualised with new projects more easily. For instance, in the recent Defra-funded OREGIN project, both forecasts were combined with weather data to predict the likely future impacts of climate change on oilseed rape diseases. With warmer temperatures, LLS was predicted to become less of a problem, but the models suggested that PSC would become more severe and move northwards to affect farms in the north of England and Scotland (ref 2).

References

  1. Development and uptake of a scheme for predicting risk of severe light leaf spot on oilseed rape .
  2. Range and severity of a plant disease increased by global warming .