The loss of Chlorothalonil: the impact on Septoria in wheat last season and how SwiftDetect could help going forward

26 October 2021

Knowing it would be a huge blow to the industry, given that the fungicide had previously been considered “the building block” of any effective winter wheat disease programme, we wrote a blog last year on the loss of Chlorothalonil and what this could mean for wheat growers in the 2021 season. 

Now that season is over, we thought we’d re-visit this somewhat controversial topic within the farming industry, and comment on the impact the loss of septoria had this year.  

Why was it 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 was the reaction? 

As you may expect, the ban of what was the most widely used fungicide in the UK since 1964 was met with concern from farming communities; in fact, 40% of farmers and two thirds of advisors considered the loss a major concern for wheat disease control. As the 2021 season approached, growers became increasingly concerned about the impact on crops without an equally effective alternative. 

How has this changed Septoria management? 

With a lack of comparative treatments, some farmers grew more resistant wheat varieties on the recommended list. Whilst this, in some cases, could have resulted in a compromise to other attractive characteristics, such varieties are thought to exhibit a degree of natural resistance to disease such as Septoria. However, it is important to point out that resistance is not the same as immunity – a comment we will re-visit later in this blog. 

In terms of alternative fungicides, growers have been relying more on older chemistry such as Azoles. This is problematic for several reasons; firstly, these are less effective than Chlorothalonil, still leaving crops somewhat vulnerable. As a result, higher volumes of the fungicide are used which could lead to issues with resistance. In addition, there is a risk of these fungicides also being removed as the Government continues to consider environmental impact.  

The impact of the loss 

Of course, if we were able to use Chlorothalonil, this would certainly have been an easier season for Septoria; unpredictable weather patterns coupled with a large gap between T1 and T2 applications put increased pressure on crops. The historic use of Chlorothalonil likely masked weaker approaches to T1 and T2 sprays, which were found wanting this season.  

There have also been concerns over the true resistance of recommended varieties. The loss of chlorothalonil coincided with the launch of SwiftDetect: our super-sensitive rapid crop disease detection test. Using a unique, patented method, we were able to test samples of wheat leaves sent to our state-of-the-art lab by post for Septoria, with results sent to customers in just 1 business day.  

Using the test, we were able to detect low to medium levels of Septoria in “resistant” varieties such as Extase, despite no visible symptoms on the outside of the leaf. Although the Septoria levels were lower than that of susceptible varieties, it does call into question the effectiveness of the scoring method of the recommended list and whether a test such as SwiftDetect could give a more accurate basis to the score regarding resistance. 

Moving forward without Chlorothalonil 

As we go into next season, there will be new wheat varieties and fungicides growers can take advantage of. However, where many new fungicides are an improvement on older chemistry, their efficacy has a long way to go to match the effectiveness of Chlorothalonil. Moreover, users must be conscious to not over-use chemicals – which will lead to resistance – and question true resistance of new varieties.  

As we previously alluded to, there is one further weapon growers can use next season: SwiftDetect. Using the test, growers will be able to determine whether their crop has disease present – even in the latent period – and if so, quantify the level of disease. The best part is, where last year SwiftDetect was only able to detect Septoria, we have developed the test to identify Mildew, Yellow Rust and Brown Rust in wheat as well as Ramularia in barley.

This will provide users with an early warning, so action can be taken before disease springs out of control. But that’s not all; by providing insight into disease levels, farmers can match fungicide dose rate and type to the actual level of disease, removing fungicide guesswork. As a result, if levels are lower than expected, a lower dosage or preventative fungicide may be used. Through this, we have had customers save thousands on their T2 spray! This will only become more important, as higher input costs are predicted for next season. 

Alternatively, levels may be higher than expected; in this case, a higher dose can be used, preventing unexpected losses in yield or reductions in grain quality.  

Another application of SwiftDetect is in the monitoring of new varieties and treatments. As a single-cost test, you can use SwiftDetect as often as you like. Some of our customers this season regularly repeated the test throughout the season, so they could learn more about how the disease progressed over time. This was particularly useful when comparing new varieties against old, as well as new fungicides.  

If you are interested in giving SwiftDetect a go next season, click here to register your interest.