Chlorothalonil’s loss is Septoria’s gain: the loss of UK wheat growers’ favourite fungicide

18 May 2020

Used across the world since 1964, chlorothalonil is the UK’s most widely used fungicide – but not for much longer. Last year, the European Union made the decision to not renew approval for the fungicide, which “almost every wheat grower has applied to wheat crops at least twice for as long as they can remember”. Sales ceased on 20th November 2019 as a result, and on the 20th May 2020 it will be illegal to use or even store chlorothalonil. In response to this, two thirds of advisers and 40% of farmers consider this loss a major concern for wheat disease control in 2020.

Chlorothalonil and Septoria

In the UK where the climate is generally cool and wet, crops are particularly susceptible to fungal diseases. As a broad-spectrum fungicide, chlorothalonil has been used to prevent and treat a range of crops for these diseases for decades; in addition, it has been used to prevent resistance to fungicides. One such disease, which is considered to be the most damaging on UK wheat causing yield losses in excess of 30%, is Septoria, for which chlorothalonil is considered a backbone in its control.

Unlike many other fungicides, chlorothalonil has remained highly effective against the disease, which has an increasing emergence of resistant strains. In fact, it is said to have a 60% control alone against Septoria; without it, farmers will have to turn to other, less effective and potentially more expensive methods, or face a significantly reduced yield. Other expected consequences include a higher level of Septoria, increased Septoria resistance and higher costs of production.

Why it was banned?

A review by the European Food Safety Authority in December 2017 was unable to falsify the possibility that breakdown of the fungicide caused damage to DNA. An additional 2017 review linked the use of chlorothalonil and other fungicides to declines in bumblebee populations, and furthermore, subsequent reviews in 2019 identified chlorothalonil as a high risk to amphibians and fish. Together, this evidence meant that the EU states voted for the ban when the chlorothalonil approval came under review in 2019.

What does the ban mean for wheat growers?

The ban has since been met with some controversy; whilst environmental groups are satisfied with the outcome, many within the farming industry have been left with a “huge blow”. There is an enormous amount of confusion, even now when we are just days away from the ban, as to what should be used to replace chlorothalonil in wheat. Some will turn to more resistant wheat varieties, though that could mean compromising other attractive characteristics, whilst others will turn to alternative fungicides. Either way, growers are likely to miss the contribution of chlorothalonil, which has been described as a “building block of any effective winter wheat disease programme”, in terms of crop profitability and resistance strategy.

The good news is, there are likely to be some new fungicides introduced to the market which could replace chlorothalonil, providing a similar level of protection but without the environmental impact. In addition to this, new rapid testing by Microgenetics SwiftDetect means wheat growers are now able to test Septoria levels in crops. They will receive results on the day after sample collection which will allow them to fine-tune the type and dose of fungicide used, helping to prevent resistance and enhancing profitability; for example, if a low level of Septoria is shown, a more basic fungicide may be used. In turn, this will save money and prevent the over-use of advanced fungicides for when a higher level is identified. In this case, whilst using advanced fungicides with curative properties costs more, it could improve yield. This has the potential to transform farming of cereal crops in the UK, preventing over-use of fungicides and reducing yield losses.

Having completed proof of concept work in 2019, Microgenetics are now conducting further field trials with a view to making the next day testing service available in 2021. If you are interested or would like to receive more information, please contact info@microgenetics.co.uk