Crop Protection: challenges continue for crop protection

Never before have we begun a crop season in a climate of such global uncertainty. The serious issues of fungicide resistance and the loss of actives like chlorothalonil and diquat have given way to much more fundamental concerns regarding our own health and the ability of the distribution system to deliver. While these are very important issues, the fundamentals within the crop protection industry remain important for growers.

The list of actives being lost to growers for crop protection continues to grow. While the headline actives to go currently are chlorothalonil, diquat and CIPC, this is likely to be added to by other important names in the near future such as fenpropimorph and dimethoate. Indeed, there are over 50 products on the lists of herbicides, fungicides and insecticides in this publication that are to go from the market soon; some have already gone. And we have glyphosate up for re-registration again in 2022. The outcome of that is by no means certain.

Loss of CTL

The imminent loss of chlorothalonil on 20 May is perhaps one of the biggest threats to our ability to control diseases in the cereals sector. We are rightly concerned as to what the loss of this active will mean for us, especially in terms of keeping septoria subdued long-term. This is especially important in terms of the protection of the new actives that will arrive in the market in this and coming years.

The loss of chlorothalonil (CTL) is perhaps an even bigger worry for barley growers, given its importance for ramularia control. This has proven to be a very aggressive fungus which has, up to now, been able to overcome all new single-site fungicide families within a few years of their introduction. The major exception has been the multisite actives, like chlorothalonil, which has withstood the test of time. Indeed, it had become more important over time for the control of this disease, rather than less so.

Introduction of Revysol

This year sees the launch of Revysol, the first new triazole active since prothioconazole in 2005. And the last major one before that was epoxiconazole in 1996. The introduction of Revysol heralds an era of hope against septoria. Its unique structure and formulation appear to be taking us right back to the early days of fungicidal disease control.

It is a new active from an old family possessing characteristics that are helping it to control all the known mutations that have developed insensitivity over the past 40 years. Its current efficacy might be described as taking us back to ground zero.

You can read more about this promising new active on pages 14-19. Claims that it can control all known mutations seem to be well founded. The belief that it will cope with future mutations may be best left to future observations, but this appears to be a unique product. Its launch has provided us with more information at the point of introduction of this active than we have known about the others following years of use. This helps add confidence to the claims.

Protection

One of our big challenges now is how best to protect Revysol. BASF would say that the best way to protect it is to use it because it is so effective. But for those of us on the outside, there is a need to find other ways to help protect it. We had hoped that 2020 would also bring Corteva’s Inatreq to the market, but it was delayed in registration and will be with us for next season. However, we still have access to chlorothalonil up to 20 May, which will cover the main use periods in winter crops.

Going forward, we ask about the benefit of adding an active like folpet to a product that seems to be able to do all that is needed by itself. The additional cost of adding a multisite may pose difficulty at farm level, but farmers above all should be aware of the need to protect our products in whatever way we can. After all, we are painfully aware of the slow pace of new product introduction in recent years.

We are aware that there are a number of other new and promising actives coming through the registration system. However, many of these are also modifications of an existing family and they are very precise single-site actives which also need to be protected. Perhaps, like Revysol, some of these may also have unique modifications which enable them to react to changes in our major fungi. This wishful thinking is important to help fight off resistance development in the years to come.

Regardless of the technical capabilities of these new molecules, we will need to be proactive to help slow the continuous development of resistance in fungi, whether that be complete resistance or a lowering of sensitivity. We should not take the arrival of Revysol and its technical capabilities as an excuse to forget what we have learned to our cost over the past two decades.

At the end of the day, the best we can hope to do is to slow resistance development, regardless of what tools we have at our disposal. Nature will continue the fight and it will always win. We have seen this with fungicides, herbicides and insecticides. Unless we work to actively reduce the natural infection pressure, we will hand the advantage back to nature time and time again. And these actions, generally referred to as IPM, are solely in the control of the individual grower.

The new push

Many growers are likely to be at least vaguely aware of the push towards a European Green Deal. This is the vision set out by the new president of the European Commission, Ursula von der Leyen. Part of this vision sets out the objective to reduce fertiliser, pesticide and antibiotic use within Europe. While these objectives have been temporarily delayed by coronavirus restrictions, they will resurface once things normalise.

We do not know what shape this is to take, whether it is to be a national usage, a reduction in the average amount used per hectare, a reduction in the amount used per hectare of a specific land use, or whether there may be a weighting given to specific actives in a new metric. But it is more than likely that this new direction for EU policy will have some direct impact on the way we farm and in the way we use plant protection products.

Against this background, it is interesting to look at what has happened already in EU and national circles. Over the past decade the number of actives registered for use in agriculture in the EU has fallen from around 900 to around 479 today. And very many of the new entries are of little use in field crops; it is estimated that only about 260 of them offer any substantial value to agriculture.

Much of this reduction was driven by the sustainable use directive and its consequences continue to have an impact. The major driver here was the switch from the risk-based system to a potential hazard approach, which set far more stringent criteria for registration. Some actives were discontinued by their manufacturers because their market size did not justify the cost of preparing for re-registration while others were banned because they could not meet the range of new hurdles that had to be cleared.

This situation is ongoing. Chemical actives need to be re-registered ever 10 years and this process presents a crunch time for every active. We remain aware that many of our existing triazoles are likely to be lost to growers soon. While these may have lost their efficacy against septoria, they could still be a useful part of disease control in barley and oats, but this now seems highly unlikely, with the probable exception of prothioconazole.

We also lose fenpropimorph this year but for commercial reasons. This would leave us very vulnerable on mildew control, but it is good to see fenpropidin return to the market. Dimethoate will also be lost to us.

Pesticide usage is down

Overall usage of pesticides in the Republic of Ireland has fallen in recent years. Figure 1 is official usage data from the Department of Agriculture expressed in terms of tonnes of active ingredient used across all sectors. The figure shows that overall usage decreased from 2015 to 2018. However, this is more likely to be a consequence of reduced area under crops due to the expansion in dairying than any significant reduction in usage per hectare.

A further breakdown of this information can be seen in Figure 2. This shows that the major reduction in recent years has been driven by the reduced usage of herbicide across the country. This again is likely to be an area effect but this is not seen across any of the other categories in Figure 2. This may be because the other input categories are also influenced by infection pressure, which can vary from year to year with problems like mildew, rusts, slugs and aphids.

Insecticide use is also a bit spasmodic, depending on pressures, and the trend in growth regulator use is mainly down, except for 2017. In comparison, the usage of molluscicides and miscellaneous products is tiny. “Miscellaneous” refers to plant protection products that do not fall into any of the other categories.

So, even though we have already reduced pesticide usage, where will a reference line be drawn for a new obligatory reduction policy. The use of a national quantity reference would strongly mitigate against any opportunity to increase our area under tillage crops and this would be regrettable. Having spent decades trying to refine product usage and rates, it is hardly feasible to cut this usage further without either sacrificing efficacy or inducing resistance development.

This poses an interesting question because the challenge to modern farming is to get rid of certain inputs rather than just cutting usage rates. This comment mainly refers to problems like grass weeds, slugs and even plant growth regulators. Reducing usage is not about cutting these out totally but rather to develop situations where they are not needed. It seems inevitable that we will have to look harder for other solutions in the future.

Resistance

The introduction of Revysol to the market this year is undoubtedly very welcome, given the ongoing evolution of resistance. But resistance is not a simple one-step process and it has become a much more complicated issue in recent years, as outlined on pages 10-13. We used to think mainly of single-change mutations but now it seems we have a number of other types of resistance evolving in different fungi.

Thankfully our chemical companies continue to work to find solutions and Revysol is just one of these. There are others in the pipeline currently undergoing evaluation for both environmental and field efficiency. We can and will look forward to their introduction in the hope that we can use a few new actives to protect each other in a sensible and cost-effective way.

This will remain a big challenge for the decades ahead. Reliance on single-site actives will always lead to resistance development and we have seen this across all input categories. However, as we learn more about resistance and how it develops, we can develop strategies that will prevent, or at least slow, the fight back by nature.

This is now being taken to a new level with the development of new actives within older modes of action which have been tweaked to help overcome the common resistance mechanisms. This is happening with the azoles, strobilurins and the SDHIs. But we must always remember that nature will continue to fight back if we give it any half chance.

Gene editing

One of the better ways to reduce fungicide resistance risk is to do all we can to decrease disease infection pressure. So decisions on sowing date, seeding rate and variety choice will become even more critical in future. There can be little doubt that varietal resistance would be among the most useful of the all these tools and this will apply to all crop challenges. But this will remain a challenge in conventional plant breeding where the delivery of one desirable trait may well be compromised by the inadequate delivery of others.

Realistically, we do not want perfect resistance to any disease. This may seem strange but perfect genetic resistance is like a strong fungicide – when nature finds a way around the defence, the breakdown can be total. It is for this reason that plant breeders have been working with genes to help identify individual genes that can exhibit a small but different impact on a fungus. When grouped together, a string of genes with different small effects can provide a very significant deterrent for any fungus.

Our problem is that this is the domain of genetic engineering and, for now at least, this is not allowed in the EU. Recent years have seen huge investment in understanding genes and their functions and, bit by bit, this is revealing more and more genes with minor effects on traits such as disease resistance.

This means that we have the potential to combine many genes to give a desirable effect but the chances of combining all of these through the random process of conventional breeding is slim, to say the least.

This is why gene editing is potentially so important for the sector. If we can make varieties with strong but imperfect genetic resistance based on multiple genes, this could be a bit like getting chlorothalonil back, but for free. And our ability to use a ‘multisite’ genetic resistance would equally help to protect the fungicide actives, of which there will be fewer going forward.

One other important benefit of stronger disease resistance could be a lesser dependence on chemicals in an era when we will be obliged to use less, according to stated EU policy. Against this background, we must ask about the potential of genetic engineering to provide resilience against other problems like BYDV or possibly even slugs. Success on any of these fronts would send a signal re the potential of genetic engineering to enable plants themselves to provide solutions for consumers.

Glyphosate

Another huge issue for the sector going forward, not just in Ireland but across all the EU, is the future of glyphosate. This has been the flagship active for the political drive against science as the arbiter for chemical safety in food and the environment. Realistically it is just another target in the long chain of attacks against Monsanto of old.

Glyphosate is a very important input in the efforts of modern farming to minimise soil disturbance and carbon loss. For many years now it has been an important input to enable non-inversion tillage globally.

While we should never have to depend on a single active in any natural system, it is important to have such an input for use where and when it is needed.

It seems that the political debate may be changing focus once again, possibly away from the claims of cancer to the destruction of biodiversity. On the latter count it is guilty, or at least its users are guilty, because that is what it does. It is a total herbicide. But how and where it is used is a label and registration issue. Only time will tell whether or not this change in thinking can help secure its re-registration in 2022. If it is to get through, it would seem highly likely that its use will be significantly curtailed. Curtailment would be easier to live with than the loss of the active.