In our recent Crop Protection magazine, I hinted of rumours of re-registration challenges for chlorothalonil (CTL). This active is very much at the centre of crop protection on this island. It has proven to be as essential for sustainable disease control as the blood in our veins is to us.

We have been aware of inevitable changes to its future use following re-registration. It was anticipated that the total use rate would be significantly reduced and that this would apply to the active rather than the product. But I did hint in that article that there was an increasing level of concern that it might not be re-registered.

There are a number of concerns with regard to CTL, which include possible carcinogenicity and concerns about ground contamination. These potentially serious issues would have been dealt with in the past using risk management, but the new legislation make it easy picking for modern political influencers.

While it is impossible for us to know how or if these factors could be weighed up or minimised by label restrictions, the loss of CTL would be a huge blow to wheat and barley production on this island.

Septoria continues to evolve aggressively to overcome the effectiveness of most families of fungicides.

Important for Ireland

This active has proven extremely important for disease control in wheat and barley in this and other countries. We depend heavily on it. It has survived the efficacy decline in all single-site fungicides, especially on diseases such as septoria and ramularia. So it remains critical for crop protection in these two crop families.

Growers on this island are heavily dependent on disease control to offset the pressures that cereal crops endure in our climate. Effective disease control is important for the protection of yield potential for the grower and the protection of crop quality for the consumer.

Failure to achieve both would condemn this country to dependency on imports. This would result in the loss of livelihoods for intensive tillage farmers and the loss of an industry which generates substantial economic activity in rural areas.

CTL and disease resistance

While CTL adds to the control of a number of diseases, it is critical for septoria in wheat and ramularia in barley. An inability to effectively control either of these diseases would be an instant challenge to the production of these crops.

Since the late 1980s, we depended heavily on triazoles to control the myriad of diseases that attack wheat, with septoria being the most serious. There has been a gradual weakening of these actives which were aided by the inclusion of other actives such as captafol and chlorothalonil.

The arrival of the strobilurins provided a new level of performance and activity. These actives set the bar for disease control and yield much higher. But their superiority was short-lived against septoria, which became totally resistant within a few years. Efficacy against most other diseases has held strong, but their failure against septoria led us to depend on CTL.

Then came the SDHIs. These too were very effective and they more than compensated for the flagging triazoles. But there was little to protect them and, once again, CTL was critical for resistance management and control of septoria. Now these too are waning and CTL must again carry a significant part of the load.

The story is broadly similar in the case of ramularia. This late-season disease of barley has long been a very aggressive disease and most single-site fungicides only show efficacy for a few years.

The SDHIs are beginning to fail on this disease in other countries and it is likely that we will find a similar picture here. This will once again leave CTL as the only effective fungicide against ramularia.

We will hopefully see some new actives and fungicide families in the market in the next few years, but it seems inevitable that these too will weaken if we do not have strong partner products to help protect them. CTL has long been important for this purpose and so resistance may appear much earlier if we do not have this active for resistance management.

On our own

In the new registration arena, politics can often override science. It is common for countries to take sides in such debates, so one needs to be in the majority camp.

The problem we face on CTL is that it is not a very important active for many member states and especially the big countries such as Germany, France or Italy. So the political challenge to CTL is even greater than for many other actives. The loss of CTL could make effective disease control virtually impossible on this island.