Having nursed a crop through the season, nothing is worse than watching golden heads full of promise turn to black or worse still, pink. The impact on quality can be huge, but yield responses to ear sprays on wheat are often erratic.
Judging the risk is very important in deciding how to protect crops. Much will depend on location, market and previous experience with ear diseases, but it also depends on growers’ attitude to risk.
What are the main ear diseases affecting wheat?
A whole complex of diseases can affect ears. Sooty moulds, like alternaria and cladosporium, are weak pathogens that take advantage of dead and senescing tissue. Others, such as botrytis, are slightly more aggressive, and then there is the dreaded fusarium family – which will often infect around flowering.
Foliar diseases, such as Septoria nodorum, which causes glume blotch, rusts and even mildew, can also infect the head. Several other diseases may become apparent, but are not controllable, at ripening like bunt and ergot. Root and stem diseases can lead to early white heads, which are more prone to sooty moulds.
What impact does each have?
Ear diseases mainly damage grain quality. Actual yield losses are usually small, but there are differences in the relative seriousness of each ear disease to both yield and quality. Sooty moulds will blacken the outer coverings of the grain and can be a serious problem in milling wheat, while alternaria can also stain the internal grain.
Glume blotch will shrivel and discolour grains and is one of the few ear diseases to also significantly reduce yield. Rust and mildew infection on the ear are not so damaging to yield as glume blotch, especially when compared with the losses they cause as a foliar infection.
Fusarium species cause grain shrivelling, often associated with pink mould, and losses in quality and yield. Of particular concern are the mycotoxin-producing fusariums.
What factors affect development?
Conducive weather is the single biggest factor affecting ear disease development. Most of these diseases are favoured by cool, damp and humid weather at grain ripening.
Most of the sooty mould spreads from ear to ear in damp conditions, often taking hold first on areas of the crop that are already stressed such as patches on light sandy soils or where aphids have been present and left honey dew.
Fusariums and michrodochium species are very weather-dependent and the precise species infecting is likely to be very much influenced by the temperature. They infect just after flowering, finding this an easy entry in wet weather.
Further north, cooler temperatures favour Fusarium culmorum and Michrodochium nivale, which is of particular concern on crops intended for seed. In the south there is proportionally more Fusarium avanaceum, graminearum and poae, all favoured by warmth and humidity.
Some varieties are very susceptible, so using varieties with better resistance like Einstein will moderate the risk. No current varieties offer complete resistance.
The single biggest worry with ear diseases is the mycotoxins formed by some of the fusarium species. This is a huge food safety issue and those species that form toxins can render grain unmarketable.
UK grain only rarely exceeds the maximum mycotoxin limits, in contrast to grain from hotter climates, but it is still an area of concern to both growers and consumers. It is also an increasing worry for the UK under some climate change scenarios.
Mycotoxins are very toxic – so much so that even minute quantities kept in labs have to be declared under anti-terrorism laws.
The other ear diseases are less serious, but can cause loads to be rejected or penalised at harvest because of quality issues. They all exist as a complex so the presence of some, like septoria glume blotch, makes the subsequent infection of sooty moulds more likely.
Using fungicides that control some, but not all, of the pathogens can also simply clear out competitors and leave the way open for other species. For example, some strobilurin fungicides will control Michrodochium nivale, but not true fusariums, which can opportunistically invade.
Ear diseases, especially michrodochium, can reduce emergence in home-saved seed.
Control (cultural & chemical)
The best chance to minimise head diseases is to optimise crop health throughout the season. Stressed crops, those with high levels of foliar disease or lots of white heads, or suffering from aphid attacks, will all be predisposed to sooty moulds. Varietal resistance and good agronomy earlier in the season can help reduce these risk factors.
Mycotoxin risk increases with maize in the rotation, and with minimum tillage.
If ear disease risk is low, a robust flag leaf fungicide spray could carry the crop through to harvest, so a specific spray might not be needed.
But growers should be prepared to spray if it’s wet at flowering, and the period of ripening is also important in determining whether a specific spray is needed. Crops that burn off early on light land are far less at risk than those in areas of more extended ripening.
Ear spray fungicides should give continued protection from foliar disease, protection against sooty moulds, and fusarium control.
Strobilurin fungicides protect against sooty moulds, rusts and michrodochium, but few control fusarium, so a mixed mode of action strategy is always advised.
Some azole fungicides control fusarium, and will also continue to protect against septoria and rusts. A mix of triazoles may extend the window of efficacy.
Adding chlorothalonil can be beneficial for additional ear brightness and prolonged septoria protection, particularly in the north.
Ear sprays should be applied between GS59 (ear fully emerged) and GS69 (end of flowering).
In this Academy, Bayer CropScience aims to ensure you “protect the quality” of your crop.
Alternatively, use Fandango as the ideal option where fusarium pressure is moderate and the flag leaf spray hasn’t controlled foliar diseases as expected, letting late brown rust through. Expect good all-round clean up of foliar and ear disease, delivering better yield and quality results than any other azole + strobilurin combination.
Proline and Fandango are registered trademarks of Bayer. Proline contains prothioconazole. Fandango contains prothioconazole and fluoxastrobin.