The development of a disease in spring barley, or any other crop, results from the combination of a susceptible variety, the presence of the fungal pathogen and environmental conditions which allow the disease to develop.

A quick look at the disease ratings of most available spring barley varieties shows that, while some have excellent ratings to specific diseases, none have the spectrum required to cover all the major diseases encountered in Irish crops. Equally, it is highly unlikely that there will be no inoculum of these diseases present in crops in spring and early summer. Even if winter barley crops were to remain relatively disease free, there would still be sufficient inoculum present, either on debris from the previous season’s crop or as seed-borne infections.

Finally, it is even more unlikely that the Irish weather will prevent disease spread and development. Taking all these factors into account, it must be assumed that Irish spring barley crops are always at risk and will require some level of disease control.

Managing the threat

How this programme is built and subsequently applied will very much depend on how the season progresses. As the 2018 spring barley season is, in most instances, only a few weeks, it could still be argued that it is difficult to determine what sort of a year this will be. Although most crops have been planted extremely late and, in general, look free from disease, the recent heavy rains combined with humid and murky conditions recently have provided ideal conditions for diseases such as net blotch, mildew, ramularia and, to a lesser extent, rhyncho.

Even with the later planting, the warm May has provided most crops the opportunity to rapidly move through the growth stages and consideration must be given to ensuring adequate filling of the grain sites created to deliver on this potential yield. The four diseases mentioned previously reduce the capacity of the crop to capture sunlight, which is essential to fill those grains.

With the exception of ramularia, these diseases have relatively short life cycles and could still cause significant leaf loss and yield reductions, even in crops that look free from them at this stage. That said, crops that have already some level of diseases present will of course be at a greater risk.

Fungicide timing

The final fungicide application must reflect any visible risk and equally the potential risk of new or other disease development over the coming weeks. However, first and foremost, the timing of the fungicide is almost as important as the specifics of what fungicide actives or rate is included.

Fungicides are expensive but, timed correctly, they can provide a significant return on investment. Between 2012 and 2015, fungicide timing trials on spring barley conducted by Teagasc have consistently demonstrated that the optimum timing for the final fungicide application is around booting as the awns are emerging. This timing has been shown to maximise the characteristics of our available chemistries and deliver good disease control combined with optimum yield.

This timing can be difficult to always get correct in spring barley in practice. A downpour of rain followed by a couple of warm days can lead to a burst of growth. However, it is important to highlight that this is what growers should be aiming for, especially this season where growth has been extremely rapid and crops may go from tillering to booting in what seems like no time at all.

It is always worth noting that while no two seasons are exactly the same, crops must always go through the same growth stages. Understanding the physiology of the crop, its vulnerabilities and how it responds to treatments is what is important. Put simply, when it comes to disease control, growers must respond to the crop and not the calendar.

What’s in the tank

What fungicide to apply is the next question? With any one of the four major diseases mentioned previously potentially threatening your crop, this isn’t always the simplest decision. As with any problem, start with the easiest one to answer.

Chlorothalonil (CTL) is now an absolute must in the final fungicide application to barley. This is specifically to control ramularia. This disease has developed resistance to the strobilurins, the azoles including prothioconazole and now the SDHIs. While it is still possible that the latter two chemistries may provide control this season, they should not be solely relied upon for ramularia control.

Trials conducted as part of the Department of Agriculture-funded EPIC project at Teagasc over the last number of seasons have demonstrated the value of CTL, especially in high pressure seasons such as 2017. In that year, some plots produced a yield response of over 1t/ha of yield.

This is a disease that responds to stress (wet, dry, chemicals etc), and often only expresses itself post-flowering. So do not be surprised if you do not see lesions in the crop at this stage. Being honest, if I was to see lesions in spring barley at this stage I would be really concerned.

The relatively low rainfall during May will have helped to reduce infection pressure but we really don’t know enough about this disease at this point. Even if this turns out to be a low-pressure season, it is still likely that the disease will be seen in crops later in the year. Furthermore, the levels of varietal resistance available for ramularia are moderate at best and even where ratings are available they may vary depending on the year.

For the other diseases it is a matter of matching the chemistry to the disease and the risk of infection. With the exception of ramularia, the main fungicides have a good to excellent profile against the other major diseases. Some slight differences do exist within the different fungicide groups and these differences can come to the fore in situations where a weakness in variety resistance exists for that disease.

It is therefore worth taking time to note the level of specific disease resistance in the varieties you are growing in conjunction with the levels of disease which are present in your crops. Final fungicide treatments should include an azole and either an SDHI or a strobilurin active at sensible and well-balanced rates. And, as stated previously, all final fungicides on barley should include CTL.

As always, it is important to ensure different modes of action are mixed to prevent either the development or build-up of resistance. And, where possible, do not rely on the same modes of action throughout the fungicide programme. There is still scope to do this in barley because we still have many effective fungicide families and this should be utilised.