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Keep an eye out for eyespot (Jan 24)

We find out why all maize-growing producers, wherever they are in the UK, should monitor weather conditions with potential eyespot infection in mind during the coming growing season.


TEXT PHILIP WINSTANLEY



Maize is a low-disease crop compared to many others, but changing weather patterns and a growing interest in grain maize mean producers should watch out for eyespot.


High rainfall in spring and early autumn 2023 played a significant role in delivering high forage maize yields across the UK. “But these conditions also resulted in the threat of disease,” says Grainseed’s Neil Groom. “An extremely wet March with continued damp weather in April led to difficult and later drilling in many parts of the UK,” he explains. “Only really light land could be drilled towards the end of April, and the majority of crops were drilled throughout May and into June.”


Looking at the UK’s maize growing areas, all saw rainfall above the 30-year average, with the exception of East Anglia where rainfall was 3.1% lower than a typical year. “While summer droughts are increasingly becoming a cause of concern for many producers, the overriding issue has been variability of weather conditions. Major rainfall events interspersed with periods of warm weather create the perfect conditions for diseases to develop,” says Mr Groom.


The good news is that maize is not susceptible to many diseases, but one that is causing concern, due to the increasing variability in weather patterns, is eyespot. This fungal disease is not related to cereal eyespot and only infects maize and sweetcorn.



Eyespot disease: know the signs and spray if required


Higher-rainfall areas


“Eyespot has typically been confined to areas in the higher-rainfall areas in west of the UK,” says Mr Groom. “Maize growers in those areas tend to spray ahead of an emerging threat to keep the crop healthy until harvest. Eyespot can significantly impact production towards the end of August and early September, with typical yield reductions of 30%. “But, most importantly for producers, it’s the loss of starch if the plants are infected with eyespot before this is ‘laid down’ in the grain that’s the issue.


“In 2023 we saw the disease begin to track east across the UK and the concern is that producers who are not familiar with the signs of eyespot could be slow to take action and to stop its spread in the future,” says Mr Groom.


This disease is particularly worrying for producers growing grain maize, where crops typically stand for six weeks longer than forage crops. “Keeping the crop green for as long as possible will benefit grain yields, so applying a fungicide to keep eyespot under control is essential.”


Early stages


Learning how to spot the disease in the early stages is vital. Eyespot is an air-borne disease and spores blow in from the west, particularly from southern Ireland. Infected plants quickly show small, round to oval translucent spots with a light-brown centre, surrounded by a purplish-brown ring with a yellow halo. The signs are pretty distinctive and difficult to mistake once spotted.


“Lesions may join together and form necrotic areas, and heavy infection can lead to premature deterioration of the leaf with a consequent loss of leaf sugars,” explains Mr Groom. “As harvest approaches, this can have a dramatic effect on feed value because, due to premature leaf death, no starch is laid down at this point.


“The end result is a crop that should yield 45 tonnes per hectare producing just 30 tonnes. And any crops affected are extremely difficult to ensile because there’s little green material and sugar to ferment,” he adds. The most important cultural action growers should take against spread of the disease is to plough in all maize trash after harvest.


“Many people will be cultivating maize stubble with tined cultivators to help rainwater infiltration and reduce soil erosion, which for most growers is the ideal approach. But in areas where eyespot is a problem it’s important to bury the trash as effectively as possible by ploughing as soon as possible after harvest.”


This is fairly straightforward with forage maize crops where there is also less potential risk because there’s only the stubble left. But grain crops and pheasant cover pose a greater problem. “The leaf and stover need to be buried to prevent inoculum infecting next year’s crops,” says Mr Groom.


“Most maize growers plough in spring and spread slurry and fertiliser on the land during the winter, and ploughing straight after harvest compromises this approach. But for slurry producers could use an umbilical system on ploughed land after the closed period and then cultivate to push nutrients into the rooting zone.”


Temperatures above 28 degrees C for a week will stop the development of the disease, so it is during cool and wet summers that we see the highest levels of infection. But, because the disease inoculum blows in on the wind, growers must remain vigilant throughout the growing season.


Disease free


If the disease is seen in July, producers should apply Comet (pyraclostrobin), at a rate of one litre per hectare, before tasselling. Comet will keep the crop disease free for six weeks after application, keeping it clean until silage harvest, according to Mr Groom.


“Producers continuously growing maize in the west and who have seen the disease this year should apply the fungicide in July as a routine protectant. The risk of infection is just too high during cool summers.”


He says that some growers worry about spraying the standing crop at this late stage, believing that it will cause a lot of damage. “But if a high-ground-clearance sprayer is used, the crop is very resilient and will bounce back with little or no problem. The only damage you’ll really do is on the headlands.”


Rotation is also key to reducing disease incidence, but variety choice has little impact. “Many growers believe that earlier varieties are more susceptible compared to later ones, but a crop’s susceptibility is largely down its actual growth stage with all being vulnerable once they approach maturity.”


Concern about the disease is such that NIAB includes eyespot inoculated trials in the Descriptive List system. “But every variety is susceptible when conditions are right, as seen in 2023.


“The bottom line is that potential changes in climate are likely to make the disease more widespread in the future,” adds Mr Groom. “All producers need to ensure they understand the disease and how to control it effectively, wherever they are in the UK.”

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