By Professor Fiona Burnett SRUC,

for the Farm Advisory Service

The final use up date for the multisite fungicide chlorothalonil is May 20, after which point it can neither be used nor stored.

The best way to use up existing stocks, is in the manner intended. So the early sprays on wheat and barley will be a key use up period where its inclusion will help manage existing disease risks.

The loss of chlorothalonil as a cheap and effective fungicide and as an aid to managing resistance risk is significant, but the decision has been made and not without some logic.

Like many multisites is was not without side effects in non-target organisms and we have to look to the future and to new tools and developments to manage crop diseases without it.

The public are more connected this season than for a long time with how important primary production is, so this is another example where adapting to the challenges posed by pesticide losses and moving forward will be key to successful disease control and sustainable markets in a post chlorothalonil world.

We have a mixed hand to play. Varietal resistance is more important than ever and it is positive that more resilient wheat and barley varieties for key diseases like septoria and rhynchosporium are now being selected and grown on farms.

We also have new fungicide chemistry that both decreases our reliance on the old but also helps plug some of the gaps.

One concern over the loss of chlorothalonil will be that is exposes underlying weaknesses in wheat and barley programmes where the chlorothalonil component has helped to ‘top up’ the efficacy of the core azole, SDHI or strobilurin components. Albeit at cost, that can be compensated for by increasing rates or by moving on to the most effective chemistry. Or both.

The launch of new chemistry like the azole Revysol this season and the novel QiI fungicide, Inatreq, next season give hopeful signs that we will be able to retain mixture and diversity in fungicide programmes. It also means we can avoid over-reliance on a few key actives where, almost inevitably, fungicide resistance would be accelerated.

Other replacement multisites like folpet and mancozeb are available. Although not as effective as chlorothalonil, they have a role in programmes and as multisites are at low risk of resistance.

If they add diversity to programmes and allow other higher risk inputs to be reduced accordingly, then they are likely to be helpful.

Specifically for wheat this will likely mean the use of folpet, with flag leaf sprays and possibly with ear sprays, although mancozeb has been shown in AHDB trials to have efficacy against ear blight symptoms, so potentially has a slot for its use there.

On barley, there is still the possibility of quite a wide range of fungicide actives, as strobilurins retain efficacy in addition to SDHIs and azole for key diseases like rhynchosporium, net blotch and rusts. That makes it possible to use mixtures and alterations more readily than within wheat.

T1 sprays in spring barleys can be reduced in low risk scenarios and the main challenges without chlorothalonil comes with ramularia management at T2.

Longer term, varietal tolerance or resistance will be key, but short to medium term we should do all that is possible to reduce other stresses on the crop and use fungicides with remaining efficacy like prothioconazole, or the new Revysol azole.


The Scottish Farmer remains dedicated to bringing you all the latest news and views from across our industry, plus up-to-date information on the impacts of Covid-19.

If you are unable to get out to pick up your weekly read, please support us by subscribing to our print edition, delivered direct to your door, from as little at £35 - or consider a digital subscription from just £2 for 2 months.

To arrange either follow this link:

Thanks – and stay safe