As if we need reminding, the announcement of the presence of SDHI-resistant strains of septoria is a sure reminder that nothing stays the same. The introduction of QoI respiration-inhibiting fungicides at the turn of the century was heralded as a new era for crop protection and production, but it was a very short-lived euphoria. Are we about to witness the same again?

For wheat growers in Ireland, the control of septoria is a key challenge. Perhaps the only foliar disease that is potentially more serious is yellow rust, but, to date at least, it is less challenging to the various fungicide families. But this too is an interesting disease, because it represents a challenge to the other facet of resistance – genetics.

It is difficult to comprehend the continuous evolution that takes place in the population of any organism, but the simple message is that change is continuous.

A monthly census of the population of septoria spores in a field might show the same levels of population genetic change as the human population might show every 30 years. But the change in the human population is easier to see, as it is influenced by age structure, social habits, the height, weight and colour of its individuals, etc.

The population of most organisms also contains a huge level of variability and different things that we do can inadvertently select for specific elements of any population.

If the human population was culled on the basis of height, weight or colour, the makeup of the world population would quickly change. Similarly, when we use chemicals to kill a big proportion of a specific population, it should not be surprising that we end up with a proportion of that population which is less easy to kill and less susceptible to specific chemical families.

This is where we now find ourselves with SDHI chemistry. It cannot be regarded as a surprise that we have found isolates of septoria that are either less susceptible to the chemistry or resistant to it. It was regarded as more a matter of when, rather than if, SDHI resistance would occur.

Other articles in this publication delve more into the issue of resistance and fungicides, but the problem is bigger than that. Three decades ago, we had only just begun to use fungicides intensively, because they worked well and their use was profitable.

Even since then, our dependence on fungicides (and chemicals generally) increased considerably to the point that we have been continuously selecting for elements of natural populations, which can tolerate or overcome the chemistry types we are using.

When you think about these facts, then resistance is inevitable, even where it has been slow to develop. To stand a chance against nature, chemistry always needs help. This can come in the form of cultural or husbandry decisions, which help to supress the amount of disease around to infect the crop.

Examples might be the delaying of planting of winter wheat into October to reduce and delay infection, or the destruction of volunteer vegetation to reduce the carryover of a disease from autumn to spring.

Genetics

The other main tool to help keep diseases and pests at bay is genetic resistance. This is a major challenge against some pathogens, but more seems possible as our knowledge of the plant genome increases.

Genetics have been used successfully to provide total resistance to some diseases, but the use of single genes to provide resistance is akin to using a single fungicide active – in time, nature and the pest will prevail.

This type of technology has long been used against diseases such as yellow rust, but once the fungus evolves to produce a strain that is not controlled, this then proliferates to take over the population and decimate the crop if external intervention is not used.

It is for this reason that plant breeders continue to work towards genetics that contain multiple genes, many of which may be only partially good on their own, but together can provide a formidable obstacle to a fungus or other pest.

Research is continuing to better understand the complexity of building disease resistance to specific diseases. Many of you may see the screening plots used by Limagrain at Seed Technology open days. This site is a hotbed for septoria infection, yet there are individual varieties present every year which remain almost free of septoria.

Yield drag

A major challenge in wheat breeding has been the yield drag that is associated with improved disease resistance. In recent years, we have seen some varieties with strong resistance to septoria work their way through the recommended list system only to be ignored in the market because of a 1% or 2% yield difference relative to the best.

While one can understand the need for the grower to maximise yield potential when forced to apply a big fungicide loading anyway, we badly need to understand where input savings can be made if using such varieties. Thankfully, this work is under way, but our reluctance to accept varieties with slightly lower yield and good resistance to septoria has slowed or prevented their delivery to the market.

In recent years, we have seen a greater interest in disease resistance and a number of newer varieties now attempt to major on this in the market. I must also say that the work being done by Drummonds in the northeast (a major wheat-growing area) is helping to identify both more resistant varieties (for example, Torp) and encourage growers to minimise their risk and exposure when growing a large acreage of winter wheat.

Pest resistance

Our problems are not just about diseases. We also have reason to be concerned about resistance issues in insects, grass weeds and broad-leaved weeds. It seems that our cropping systems are throwing up more and more problems and more and more grass weeds. A few decades ago, we began to tackle a wild oat problem. Now there is hardly a field (less than 5% anyway) that does not have an annual need for wild oat control or rogueing. Why did we allow this to happen?

The worry now is twofold; the ongoing cost of control and the likelihood of resistance. Total dependence on herbicides makes resistance inevitable, as this has already happened in other countries. While resistance in grass weeds has not been a significant issue for us in this country, the confirmation of wild oat resistance to Axial could represent the start of this slide. That, plus the movement of a range of grass weeds to different areas of the country, magnifies the need to be very cautious about where machines, seed or other materials coming into your farm have come from. There are very many potential sources of resistant or new weeds.

While grass weed resistance has not been a major issue up to now, I am glad to hear that Tim O’Donovan of Teagasc is about to co-supervise a PhD on the topic of grass weed resistance in Ireland, beginning this June. This research will focus on wild oats, canary grass, sterile brome and black grass. This is very important research, because we need to establish how these weeds are moving throughout the country and to what level resistance to chemicals may already be present in weeds such as blackgrass if resistant seeds were already imported on straw, seed or machinery.

But whatever the status of chemicals, I believe that all farmers have an obligation to contain and control these menacing weeds on their land. I am reminded that wild oats as a crop weed was virtually eliminated in Sweden, because farmers had a legal obligation to control all of them to prevent seed return. There, the public could report any failure to comply. It may be too late for zero tolerance here, but anyone with four different grass weeds to control may not have a rosy future in cereal production, so using every means to keep them out or reduce numbers has to be a good investment in one’s future.

Professional users

Meanwhile, the professional user (PU) legislation has come into force since last November. The message eventually got through, and many farmers completed the basic boom and knapsack spraying courses, which are a prerequisite for the application to be a PU. But I must reiterate that a sprayer course in itself is not what is needed. If you intend to apply spray, you must personally register as a PU with the Department of Agriculture.

Since 26 November 2105 all professional use pesticides could only be applied by a PU. You may have completed a course, but that does not comply with the Sustainable Use Directive requirement and if you do not have a PU number issued by the Department, then you are not permitted to apply pesticides. One can still complete a spraying course or, having done that, apply to be a PU, as this is an ongoing process. But you cannot apply products ahead of the date on which you receive your PU number.

While there were many complaints about the necessity to be registered as a PU and having to do a sprayer course, the fact remains that we are seeing an increasing amount of pesticide appearing in our water courses. While the problem is mainly with grassland herbicides, crop products are being found also.

The bottom line is that someone is not exercising sufficient care to prevent pesticide movement, either as spills, drift or careless application. Pesticides in water will inevitably lead to use restrictions and, sooner or later, prosecutions.

The fact is that protection of water is not a matter of choice. If we, as users of pesticides, are in any way careless about how we use these products, then use-constraints or deregistration are inevitable. It is up to every user to ensure that products are used sensibly and within the guidelines provided on the label.

Fewer tools

The fact remains that the number of actives and products available for use is decreasing annually – more about this elsewhere. The availability of a range of active types across herbicides, fungicides and insecticides is critical for the management of the individual problems and the prevention or slowing of resistance build-up. The situation with regard to SDHIs and septoria is well known. But now we have another two insecticides removed from the market in a scenario where we already have resistance concerns in the pyrethroid group.

The continuous reduction in the number of actives in the different markets is enhancing the probability of resistance in all use categories.

But one must also say that alternative chemistry was not used to protect widely used chemistry, such as sulfonylurea herbicides, even when they were in the market.

There will be new molecules developed, but it is increasingly difficult to get these across the line to commercial availability and use. And from a grower’s perspective, it is increasingly difficult to justify the increasing cost base that continues to erode the potential for profit.

Perhaps the greatest challenge for the future is the affordability of crop protection products, especially as they weaken in efficacy. As a nation, we must awaken to the necessity to minimise dependence on chemistry that is increasingly unaffordable, even where efficacy is unquestioned. When the sum of all costs frequently exceeds the likely value of the income, it is time to begin to sing from a different hymn sheet, even if only on some of your acreage.

Margin pressure

While all of the previous aspects relate to our ability to protect our crops long term, there is little doubt but that the bigger problem in the sector is the shrinkage of margins through the increase in costs and the fall in prices. Recent global grain surpluses have severely impacted on prices to make production unprofitable in many countries. In this scenario, one musty look seriously at the decision made for every acre in the short term.

Only acres that are likely to produce good yields should be planted, as unprofitable acres merely produce tonnes at a loss that help to maintain the surplus in the market to depress the price. This seriously challenges the place of poor-quality rented land for crop production.

Quality of advice

One other thing that must be mentioned before I conclude – this is a serious time for all growers and not just wheat growers. But the SDHI issue makes advice on disease control in wheat very important, as it may be impacting on our (the nation’s) ability to produce winter wheat into the future. Pesticide advisers have a huge responsibility in this regard, and growers getting advice which deviates from the norm should be wary of such advice, because any short-term gain achieved may go further to threaten your future ability to produce this crop.

To read the full Crop Protection Focus Supplement, click here.