So far the 2019 growing season has, like 2018, been atypical, but unlike last year, we had a spring. Indeed, it could be argued that at some stages the spring crept into an early summer, with above normal temperatures experienced from January to April.

While rainfall for the same period looks normal, this does not give the whole picture. February was generally below normal for rainfall, but this was balanced by above-average rainfall for March. The combination of fluctuations in rainfall and slightly higher temperatures has been ideal for the development of the typical foliar diseases experienced in Irish winter wheat crops.

Yellow rust was also quite troublesome this year and in some instances this was difficult to control. These difficulties in yellow rust control were exacerbated by unfavourable weather conditions for spraying as the third-last leaf emerged and this resulted in suboptimal fungicide timings. In those crops where yellow rust was kept at bay, the broken weather at the time was exploited by septoria, with lesions appearing on the third-last leaf and in some cases, on the second-last leaf.

Fortunately, the weather throughout May has been extremely favourable in terms of fungicide application and timing and most flag leaves have received protectant applications. While the infections that occurred in the lower canopy are of concern, the extremely reduced rainfall during May, specifically when the flag leaf was emerging, combined with ideal spraying conditions at the same time, will hopefully have limited any potential disease development on the upper leaves, which contribute most to yield.

From heading onwards

Taking this into account, the next task is to ensure that the potential which has now been created is maintained. As we enter June, the control of disease on winter wheat relates primarily to fusarium or ear blight.

Fusarium head blight, also known as ear blight, has the potential to cause significant reductions in yield. While instances of the disease have been sporadic over the past number of years, each season there are cases where potential yield has been lost.

In those crops where infection took place over the past number of years, significant reductions in yield and quality did occur

If we are to remember the last year of serious widespread ear blight infections, we need to go back to 2012. Instantly we will all recall that this is not a season that we want to remember or experience again. However, in those crops where infection took place over the past number of years, significant reductions in yield and quality did occur and fusarium should certainly not be ignored.

That said, fusarium infections are very much weather related, and if high pressure takes hold during the first couple of weeks of June, with little rainfall, we can expect fusarium levels to be low. Given the unpredictability of our weather up to now in 2019, hoping or expecting that it will remain fine for the first couple of weeks of June could just be wishful thinking. Bearing this in mind, what actions should growers be taking to minimise this risk?

Preparing for T3

The first thing to do is to understand the risk your crop is exposed to. While we are not yet able to reliably predict what level of inoculum may be hanging around commercial crops, we do know some crops will be at greater risk of infection.

The first aspect that should be looked at is the specific variety grown. There are differences in genetic fusarium resistance, and knowing this is vital.

Knowledge of the local environment in which the crop is growing is equally important

If conditions in early June favour disease development, time is of the essence in terms of fungicide application timing. Knowing what crop to put most emphasis on is therefore important. Similarly, knowledge of the local environment in which the crop is growing is equally important. For example, a location where mist tends to settle first in the evening and burn off slower in the morning is likely to hold moisture, especially when it rains. These areas should be the ones that get most attention, especially when fungicide timing is of the essence.

The choices

What can be done to protect against fusarium then becomes the question. First and foremost, we must remember that when fungicides are applied they affect not just the target disease, as they can also select for resistance in other diseases.

If a blocking, high-pressure weather front moves over Ireland, the widespread application of fungicides may not be required at heading time

For this reason, we should minimise their usage where possible. Therefore, it should be emphasised that for fusarium control the application of fungicides must reflect the pressure that exists.

As mentioned previously, if a blocking, high-pressure weather front moves over Ireland, the widespread application of fungicides may not be required at heading time. Understanding the conditions as described previously becomes equally important, as even with settled, dry weather, there may indeed be fields that will still have a risk of infection.

Timing

Unlike the foliar diseases, the period of protection required is different. For example, in the relationship between leaves and foliar diseases, such as septoria, infection can occur from leaf emergence through to senescence (however, we only need to protect the upper leaves). But the period of infection for fusarium and the ear is mostly during flowering. As such, there is a relatively short window during which fungicides can be effective.

As the timing for protection coincides with infection, monitoring weather forecasts and crop growth stages should become a full-time job from the point of ear emergence (of course this becomes a lot easier when that blocking high pressure takes hold). As the crop is at greatest risk from infection during flowering, protecting the crop with a fungicide at this point is critical.

Unfortunately, as flowering is a process it doesn’t just occur all in the one go or at one point in time.

Control levels for fusarium are often quoted in the range between 50-60%

This means that there is no single point during which the entire ear can be protected by fungicide.

Flowering is a process that occurs over a number of days and this restricts the ability of fungicides to achieve 100% fusarium protection.

Control levels for fusarium are often quoted in the range between 50-60%. This reflects how much of the ear may be protected during the application of a single fungicide. Unfortunately, to some extent, this is something that we have to live with.

The aim of the final fungicide application must be to maximise protection as much as is feasibly possible. This is best achieved by applying fungicide at the mid-flowering stage.

Again, like the previous fungicide applications, it is important to know the specific growth stage a crop is at, and to make decisions on when to spray based on this information and the weather forecast at the time.

Fungicide products

Ear blight disease is caused by a complex of different species, including both Fusarium and Microdochium species, so the choice of fungicides is somewhat different to those used for septoria, for example.

To maximise the potential for the control of Fusarium species which can cause disease, azoles such as prothioconazole, metconazole or tebuconazole should be used at the appropriate timing.

That said, prothioconazole is currently the most effective active against the Microdochium species.

In brief

The final or T3 fungicide spray on winter wheat is always somewhat uncertain because you do not know if it will be beneficial or not at the time of spraying.

Assessing the infection risk in your fields is an important part of the decision to spray.

Fungicide mixtures may be necessary to control the broad spectrum of potential diseases.