Finishing winter barley protection

Almost all growers now have some winter barley on their farm. Last year has shown us that there are significant challenges in consistently achieving high yields year in, year out. Weather can play a significant part but grower management needs to be of a high calibre to achieve the highest yields.

The 2016/2017 season has been relatively kind. Excellent establishment last autumn and good early season growth has set up the final spray in crops with excellent shoot counts with many in excess of 1,000/m². This is where the crop needs to be to achieve maximum yield. Low rainfall has also been a positive factor in reducing disease pressure. But the impact of weather during grain fill and late season disease control will be the final arbitrators of yield. This article outlines where disease control plays a part and where the final fungicide can add money to the bottom line or cost money.

Yield formation

Achieving a high yield of barley is highly dependent on producing a crop with a large number of grains per square metre. It has been found that high-yielding barley crops produce 18,000-20,000 grains/m² and that ear number has the greatest influence on grain number, while grain weight is not a large factor. Therefore a thin crop, or a crop with a low ear number, is unlikely to achieve a high yield because of the inability of a barley crop to compensate through higher grain weight. Wheat, on the other hand, can compensate for thinner crops with more and heavier grains.

Fungicides play an important role in achieving high ear numbers, especially in the early part of the season where early disease can reduce the number of tillers produced.

Teagasc trials from 2010-2013 examined the return from five key fungicide timings:

All combinations of each of the five timings were evaluated at two sites, a high disease pressure site in Cork and lower disease pressure in Oak Park in Carlow. The treatments in all cases were Proline 0.4l/ha plus Venture 0.75l/ha or untreated. The results (Figure 1) showed that three timings – mid/late tillering (< GS30), stem extension (GS31-32) and awn emergence (GS39-45) – give a good response to fungicides with the best response coming from the stem extension timing at GS31-32. The earlier timing of mid/late tillering to GS30 gives a good response when disease challenge is high and always gave a higher response in Cork (high disease pressure) than in Oak Park (low disease pressure).

Timing the final fungicide

There are no additional benefits from applying a fungicide once the crop is headed out. In the timing trial, applying the final fungicide at awn emergence (GS 39/45) out-performed fungicide application at ear emergence (GS59), whether as a single application or as part of a fungicide programme. And the response to this final treatment timing was higher at the higher disease pressure site in Cork.

The later fungicide timing after ear emergence resulted in a yield penalty at both sites. The biggest late-season disease target in barley is ramularia. Control of ramularia is protective and must be applied before the disease is established. For this reason, there is little benefit from applying a fungicide when ramularia is already established. Hence the critical importance of timing for this disease.

Role of final fungicide

The function of the final fungicide is to prolong light interception through the retention of a green canopy. The final fungicide in winter barley targets ramularia protection and also provides a top-up for rhynchosporium, net blotch, rust and mildew control. Mildew was the predominant disease in the early part of this season but it has been well controlled in most crops.

Ramularia

Typical symptoms of ramularia are small brown rectangular lesions surrounded by a yellow halo and can sometimes resemble the spot form of net blotch, which we have seen in some crops this year. One of the distinguishing features of ramularia is that it can be seen through the leaf. Sometimes symptoms can be seen on lower dead leaves, as detected in Oak Park earlier this season, but normally symptoms appear post-flowering. Crop stress caused by drought, waterlogging or flowering, has been investigated as one of its triggers.

Role of chlorothalonil

Bayer in Germany recently confirmed the presence of two new mutations that affect the performance of the SDHI and azole fungicides on ramularia. Resistance in ramularia to the strobilurins had been previously detected and such strains are now regarded as widespread. While there is no evidence of resistance in ramularia to the SDHIs or azoles in Ireland, the information from Europe emphasises the importance of using the multisite chlorothalonil (not cleared for this use in many EU countries). This remains very effective in the control of ramularia in the final fungicide timing. Chlorothalonil is also a useful tool as part of an anti-resistance strategy to protect other chemistry groups (azoles, SDHIs).

An effective final fungicide mix

Firstly, it is important to walk the crop before deciding on product selection for the final fungicide. Mildew may be missed without a proper inspection. Chlorothalonil is a must for every crop to control ramularia. We are fortunate that we have a good range of products to control disease in barley and successful control is being achieved with the main fungicide groups: SDHIs, triazoles and strobilurins.

A minimum of two actives (in addition to chlorothalonil) should be used at this timing, to provide effective disease control and also as part of an anti-resistance strategy.

A recent Teagasc trial looked at four varieties – Cassia, Retriever, Volume and Tower – sprayed with a mix of Proline (azole) and Jenton (strobilurin + mildewicide) at quarter, half, three-quarter and full rates at two sites. This research found no significant increase in yield response beyond the use of half rate of the fungicide mix.

The clear message from this trial is the best return for fungicide spend is to apply no more than a half rate of a mixture of two different actives (eg azole + strobilurin, or azole + SDHI), but always include chlorothalonil.

Many of the products currently available on the market are in pre-formulated mixtures of triazoles, and strobilurins and/or SDHIs, so select a rate that will supply no more than half rate of each component of the mixture. Where possible, rotate fungicide groups applied to the crop throughout the season.

Most importantly, watch the spend at the final fungicide timing. The response at this final timing can be small with an average range of 0.14-0.4 t/ha depending on disease pressure.

Growth regulation

The final timing for growth regulation is awns visible (GS49) and some crops may be past this by now. For those not there yet, make a last assessment of lodging risk. This should be based on previous growth regulation (very effective in some cases), varietal characteristics, shoot number and total nitrogen applied. This can be applied with the final fungicide. In some cases, the total area of the field may not require growth regulation and applying a growth regulator to the ins and outs and the overlaps in the short ground may suffice.

Learn to the end

Finally, just because the final spray has been applied does not mean that the gate should be shut while waiting for the combine. A lot of valuable information can be gained from crop inspections late in the season that could be used to guide future decisions.

When the crop is starting to ripen is an ideal time to assess the presence of grass weeds and to get them identified then rather than missing the opportunity during a busy harvest. Remember, whatever you have pre-harvest is likely to be next season’s problem and a chaff spreader on a combine will help to spread it all over your field.

The author would like to acknowledge the research work carried out by Liz Glynn and John Spink at Teagasc Oak Park, which was used in this article.