After the heavy rains last February, the relatively dry March and April were most welcome across the country. Winter crops picked up from a poor starting point and field operations were completed with ease and in good time. However, this dry spell has now stretched into May and potentially beyond.

Unfortunately, 2018 and its drought, which severely affected spring cereals, is still fresh in the memory. The question now is whether the same will occur in 2020 or will crops thrive more in the heat? The answer to this will only become apparent in the coming weeks.

However, unlike 2018, most of this year’s spring crops went into the ground early enough and in good conditions. In most cases, establishment was exactly where we would want it to be. Hence, in general, there was good yield potential there from the start.

There are of course some exceptions, particularly some late-sown crops that struggled from a lack of moisture from the get-go. But we must remember that a crop’s potential is not just about establishment. What happens thereafter has just as big an impact, with disease, crop nutrition, or even drought all playing a role.

While most of the country has not had a shower of rain for well over a week, there were some heavy rains prior to this at different times and in different regions throughout May. However, as these showers tended to make their way across the country they fizzled out and, although heavy bursts of rain were experienced, the worst of the impacts of drought are evident throughout the eastern side of the country. The result is almost a patchwork of crops with varying yield potentials throughout the country.

Crown rust can still be an explosive disease in susceptible oat crops.

Assess risks versus potential

These differences in rain events have also led to differences in disease levels that will equally require different fungicide control strategies. It is vital at this stage to be realistic as to what potential exists in your crop and to match the disease control programme accordingly. If yield potential does not exist at this point then, unfortunately, the most expensive fungicide programme will not create the yield at this stage.

Equally, if good potential exists now then it is important to ensure that it is realised. While short-term weather forecasting can provide us with an idea of the coming week’s rain, or lack of it, spring crops have yet to start filling grains and we can only hope that decent amounts of rain will have fallen by the time grain fill gets under way. While rain may create issues with diseases, those are issues that we can at least try to overcome, as detailed in this article.

The disease protection of winter barley and oats is now completed, so this article concentrates on the crops where fungicides are still likely to be applied.

Winter wheat

Septoria has been kept very much in check by the lack of rain over the past month. While grain fill has yet to start, the potential impact of septoria diminishes with every day that passes without substantial rain. So, our attention turns to the final fungicide.

Ideally, this fungicide should coincide with crop flowering. Its purpose is primarily to protect against ear diseases, with residual protection of the flag leaf. Therefore, we must determine infection risk and match this to the fungicide application.

Fusarium head blight (FHB), caused by a complex of different fusarium and the microdochium species, is the main disease risk. The disease needs rain to get it going and a couple of wet days around flowering can cause havoc. Unfortunately, these same conditions do not allow spraying.

We must equally acknowledge that it is almost impossible for a single fungicide application timing to protect the entire ear from infection. Therefore, while fungicides can provide good protection, there is only so much they can do. As such we must time this application to maximise control, hence the recommendation is for mid-flowering.

Good efficacy

Similarly, not all fungicides will have equal activity. The azoles, tebuconazole and metconazole have good efficacy against the true Fusarium species, while prothioconazole also has activity against the Microdochium species. Hence a mixture of azoles is often recommended at this timing.

Although septoria pressure may be low, if the weather becomes favourable for FHB infection you can equally expect that septoria will also be moving. However, the activity of the fungicides applied to target ear diseases should also give sufficient control of any septoria that may still develop.

However, given the warm and dry weather we are experiencing, brown rust, which is not normally a disease that we see very often, could make an appearance.

Again, components of the ear fungicide (eg tebuconazole) should be sufficient to provide protection.

Alternatively, if the risk of FHB remains low, but brown rust is evident, a strobilurin with brown rust activity (eg pyraclostrobin) can be applied.

Spring wheat

Spring wheat crops may not yet be at the stage for final fungicide application as many will still require a flag leaf spray. Mildew and yellow rust are generally the biggest concerns, especially as septoria has been kept to the base of the crop.

Both the lack of rain and the higher temperatures experienced at the end of May, combined with the sharp frosts during mid-May, will have kept yellow rust in check. However, if the weather cools and we get rain over the coming weeks it could get going again. Mildew, on the other hand, will move fairly quickly if moisture becomes available and this does not have to be heavy showers. As such, Those at the flag leaf application should keep these in mind.

Disease pressure is low at the moment and fungicides are likely to be applied protectantly, so rates do not have to be as robust as they would typically be. The fungicide actives used should reflect the target diseases, with prothioconazole-based products providing good activity on mildew, while a strobilurin or specific SDHIs can be added to control rust.

As is the case with winter wheat, the risk of FHB will be determined by the weather as the crop starts to flower. If it turns wet during flowering, then the risk increases, and ear blight protection will be required as described previously.

Ramularia is always a serious threat on barley crops, especially in times of crop stress.

Spring barley

Poor sowing and establishment conditions for winter crops last autumn and winter have led to a larger area of spring crops being sown this year, and in particular spring barley. Most spring barley crops got off to a good start, with ideal sowing and establishment conditions. However, as mentioned earlier, there are some definite exceptions, particularly late-sown crops that struggled from a lack of moisture from the start.

The prolonged dry weather that much of the country has experienced has led to very low levels of the main diseases such as rhyncho and net blotch in most crops. Although most spring barley varieties now available have high levels of mildew resistance, some of the older varieties are susceptible.

However, mildew levels still appear to be low in these varieties too. But if rain does come in the next few weeks expect these diseases to start moving through crops.

Most crops are getting close to the timing for their second fungicide application. The ideal timing for this is GS39-49 when the flag leaf is fully emerged through to the awns starting to peep. Teagasc trials have shown that delaying this spray until the ear is fully out (GS59) can lead to a yield loss of 0.4t/ha. The prolonged moisture deficit is a stress in itself and if rain does arrive over the coming weeks it is inevitable that ramularia will appear in crops.

With this range of potential target diseases, the fungicides applied at this timing should be similar to those applied at tillering. This means a mixture of an azole plus an SDHI/strobilurin, with the addition of folpet for the control of ramularia. If disease pressures remain low, rates can be lowered as they are being applied more protectively than curatively.

Equally, choice of actives included can be adjusted to reflect the pressures.

However, irrespective of what is applied, it should be a mixture of actives providing similar efficacy to delay the development of resistance. While chlorothalonil used to be an automatic inclusion at this timing, it should be noted that it is no longer approved for use since the 20 May last so it should not be included in the second fungicide application.

Spring oats

Spring oats have developed well and, like the other spring cereals, disease levels are generally low. Most crops are not ready for the final fungicide application just yet, which is typically applied when the ear is half out.

Crown rust and mildew are the most likely diseases that will develop later in the season, with particular attention needed on crown rust as it prefers warm and humid conditions. This disease can also potentially cause significant reductions in grain yield and quality if it is not controlled. As such, a fungicide mixture targeting mildew and crown rust is required to give good control.

Again, as in all situations described previously, monitoring of disease levels is vital to determine local pressure and to aid decisions on what fungicide products and rates are required. If disease pressures continue to remain low, rates can be reduced from the levels that would typically have been used. However, it is important to remember that mildew and crown rust can reappear quite quickly in crops and if temperatures decrease during June we could yet have a potentially long grain filling period.

In short

  • Decisions on the choice of fungicides should be driven by the main disease risks in a crop and area.
  • The rates used may be adjusted for disease pressure and risk, and also for the yield potential of the crop.
  • If the weather takes a turn for the worse in the near future, then ear blight and ramularia could still be serious challenges and grain fill could be prolonged.