How quickly the season slips by. We enter another June and this means most crops will shortly receive their final fungicide sprays for the 2014 season. So far, the season has been relatively kind with reasonable spraying opportunities amid some delays. Many spring crop sprays with herbicide, aphicide and insecticide had been delayed up to last week but this work is done by now.

So far 2014 has been a relatively low pressure year but this is changing rapidly in some areas. Last season’s dry conditions seem to have knocked all diseases. And yet net blotch, which was barely evident in fields in 2013, became a virtual epidemic on volunteers in stubble over-winter. Thankfully this has failed to re-infect spring crops to any degree so far.

That said, septoria levels are now increasing exponentially in some crops in north Leinster. But this should not distract from the need to be concerned about other diseases. In this article, I look at the main diseases that we must continue to watch out for in our main crops.

Rusts

Many growers, especially in the north east, had to deal with the added pressure of both yellow and brown rust this spring. Crown rust on oats was also a problem in a few regions. Left unattended, these diseases could quickly cause serious defoliation and yield loss, even early in the spring.

Yellow rust is a particularly nasty disease and arguably among the worst of the yield robbers – up to 60%. Despite all the attention given to septoria, its yield loss is normally just over half this level.

It was for the control of rusts, and yellow rust in particular, that the pre-T1 or T0 fungicide was developed in Britain. Serious rust infection could result in severe defoliation which could make septoria a non-entity.

The main problem has been yellow rust in both wheat and barley but brown rust was also around on barley. The one thing that we must remember is that you never win the battle against rusts in the year of infection. Once infection is in your crop, or in the immediate area, you must view it as a serious threat.

This target disease should not be forgotten in the final spray. If final fungicides are applied early this year, and if harvest is normal or later, rust diseases can reappear late in the season and cause real trouble. So, keep it out.

Ear blight

This is an all too common disease in this country. It comes in after all of the other inputs have been applied to devastate both yield and quality, especially in wheat.

Limited control seems possible (see other articles) through the application of Proline-based products but only at high rates and high triazole loadings.

Such spend may seem like an expensive insurance at T3 given that its profitability is often called into question. However, in seasons where our weather is dominated by cool damp conditions during flowering, this seems like a worthwhile insurance input. It is arguably even more important where growers have sold forward at a designated minimum quality spec.

As per the articles on pages 4 and 7 of this supplement, prothioconazole is an important ingredient in the final spray, especially in high ear blight pressure situations. Where the pressure is moderate to low, other actives or combination of actives, such as Prosaro, Gleam, Magnello, and high rates of epoxiconazole, metconazole and tebuconazole can show useful but often modest effect.

In high pressure situations application rate is critical. This is a difficult challenge and rates need to be robust. Why risk less than full rate when you know that pressure will be high?

Additional loading through triazole mixes helps. Timing remains uncertain but the recent UCD work would indicate that later flowering could still be very useful when disease pressure is high. Putting the spray in around the rachis is also a challenge so forward- and rear-facing nozzles should help.

Where ear blight is a real threat go for big rates, big triazole loadings and a well-targeted spray application at mid to late flowering.

Septoria

Over the past week or two septoria has moved up in both unsprayed plots and sprayed crops. Septoria lesions are now visible on second and flag leaves in some crops in north Leinster. Rainfall was high in this region in May and T2 fungicide timing was less than ideal.

If septoria is highly threatening at the time of the T3 spray, its control may take precedence over ear blight. But the high triazole loadings required will provide the best solution for both diseases.

Hopefully, we will see drier weather in the weeks ahead which will decrease the pressure from both diseases.

Mildew

Mildew was a problem early on but generally faded in the combination of wet and dry conditions. But now, crop canopies have filled up so well that high humidity can be expected which, given appropriate temperature and humidity, could see the return of mildew late in the season.

It is some time since we had a problem with ear mildew on wheat but it could yet appear.

Watch out for it but there is little point in applying morpholines unless it is present. Late-season mildew is seldom a problem in winter barley or oats unless there is latent infection already in the crop.

Spring crops could be at risk though as high soil moisture levels interact with high canopy densities.

Rhyncho

Rhyncho remains a major threat to spring barley. Some crops already have some infection while all others are at risk. It is time to have the majority of April-sown crops covered with fungicide. Because rhyncho is the major threat, prothioconazole is the main single active. However, for those using a triazole SDHI mixture, Siltra, Skyway, Mandarin or Ceriax provide product choice. Bontima provides a good option to help spare the triazoles.

Final sprays on spring barley must cover against rhyncho, rust, net blotch, ramularia and, possibly, mildew. Most of these diseases can be covered by triazole mixes with either an SDHI or a strobilurin, plus chlorothalonil or Phoenix for ramularia control.

Protection against rhyncho must be preventative so have sprays on in time.

The significance of the disease threat to wheat may be escaping the direct attention of wheat producers around the country. Scientists increasingly feel that we are living on borrowed time with regard to our ability to control septoria. We all know that our long-serving triazoles have weakened considerably in recent years and the strobilurins have developed almost complete resistance. We are, therefore, depending more and more on the SDHI actives for satisfactory control of this disease.

So far, these are performing well at field level. However, studies in controlled conditions have shown a number of potential mutations to be possible, any of which could render these actives useless against septoria. Signs of this inevitability have already been found through the detection of resistant mutations in parts of Europe, so it is only a matter of time before it lands on our doorstep.

Resistance in septoria to SDHIs is seen by scientists as inevitable rather than possible. The main uncertainty is when this will happen. When this occurs, the production of wheat in this country will effectively cease because losses due to septoria are likely to be over 30% annually and up to 50%. Our penalty for the development of septoria resistance will be severe – a probable abandonment of wheat production.

Barley is also at risk of resistance problems developing to SDHIs. However, for the time being at least, the major diseases like rhyncho and net blotch show good sensitivity to a range of fungicide families, all of which help protect the other. But there are issues already reported on SDHIs and net blotch, so long-term control cannot be taken for granted here either.

Robustness is needed to give our fungicides a chance but that comes with a price. Rotation is key to helping keep disease pressure down.

  • So far, 2014 has been a relatively low disease-incidence year despite high pressure circumstances for wet-season diseases.
  • Rhyncho has taken a grip in some spring barley crops but most were sprayed before infection took place.
  • Septoria levels have increased considerably in some fields in recent days, especially in the north east, where there is a higher density of production.
  • Care is always needed to protect the tools we are so dependent on in this country.