Current grain prices as well as the experience of last season may tempt growers to cut back on spend for the coming spring fungicide campaign
Current grain prices as well as the experience of last season may tempt growers to cut back on spend for the coming spring fungicide campaign but, according to experts, there is an increased argument for maintaining optimum, preventative input strategies from the T0 timing onwards if crops are to realise their full potential. Dominic Kilburn reports.
With as many as 1.8 million hectares of wheat in the ground, a mild autumn and winter, crops well established, lush and seemingly full of potential – what can go wrong as growers and agronomists begin to asses and plan for the spring fungicide campaign?
However, while admitting he’s at risk of repeating himself on an annual basis in recent years, NIAB TAG technical director Bill Clark (left) reckons this season really is on-course to be the worst ever in terms of yellow rust infection; with high levels of “an aggressive strain” affecting a lot of wheat crops since as early as last autumn. In addition, brown rust, mildew and septoria, are all being found at significant levels this spring.
According to Mr Clark, the real concern is that the pressure being put on farmers from low commodity prices, as well as the relatively low disease pressure seen in wheat crops last season, may tempt many to cut back on fungicide spend.
“Commodity prices should have little impact on what farmers are doing in terms of fungicide applications this spring,” said Mr Clark, speaking at a cereal disease control briefing hosted by crop protection company Syngenta.
He explained that he has developed a computer model for 2016 looking at the effect of fungicide inputs on winter wheat. Developed for the ARTIS training initiative, the model shows that, as fungicide input increases, so too does margin, before flattening off at the optimum and then tailing off only gradually once the optimum is passed.
The model also indicates that, for both responsive and less responsive varieties, the wheat price has relatively little impact on the optimum fungicide level, added Mr Clark.
“In 2012 I started looking as to how responsive varieties compared with unresponsive,” he continued. “So called ‘dirty’ varieties may have low untreated yields and a higher requirement for fungicides than ‘cleaner’ varieties, but as you spend money on fungicides, their yields go up fast and then plateau.
“I did this model when prices for wheat were much higher and, as an example, in a high disease situation at a price of 130/t the model provides the optimum spend for a variety, but if the price of wheat drops from 130 to 110/t, the margin only drops by 5-6/ha, and so that’s how much you need to reduce your input spend by.
“Farmers think they can spend a lot less money, which is a risk, and if they spend too little on protecting their crops in a bad disease year such as 2012, their margin will be low and three times worse than spraying too much in a low disease year,” he highlighted.
Get it right
Compared with the more obvious signs of yellow rust in crops throughout the autumn and winter, Mr Clark suggested that predicting septoria levels this spring would be far more difficult. He said that at the T0 timing growers will get an indication of just how bad infestations are and at some point they will have to make the decision as to whether it’s a bad season for disease pressure or not. “An SDHI will be needed at T1 and T2 in a high disease pressure year and, in a low pressure year, trials have shown that it’s better just to drop the dose of the SDHI rather than take an SDHI out of the programme altogether.
“A full dose of a triazole on its own has short eradicant activity and cannot eradicate infection that is already on leaf 2,” he pointed out, adding that timing of products this spring will be key.
Bill Clark’s top tips for disease control this spring
– Timing of fungicides more important than dose- Product choice now more critical in high disease situations- Triazoles alone or with CTL not good enough for septoria control- SDHIs vital in high septoria situations- Must use mixtures of SDHI and triazole- CTL is important at T0, T1 and perhaps T2
With the T0 fungicide timing approaching, Syngenta field technical manager Iain Hamilton (left) emphasised the importance of the early fungicide applications in preventing septoria getting out of control for the remainder of the season.
“With potentially high levels of disease in crops, and a lack of curative chemistry, we cannot let septoria get out of control,” he commented. “Growers must look at the importance of the early timings to prevent disease getting out of hand by T2.
“There is a correlation between rainfall levels in April and May, and septoria levels, and so you don’t know what will happen during the next few weeks. You can be in danger of losing yield at different timings and if you get it wrong early you never recover the loss,” he explained.
Mr Hamilton added that while the T0 spray was critical in terms of reducing the risk from over-wintered septoria and rust, the application also helps to mitigate against any delays that may occur with T1.
Highlighting the need for a good mix of chemistry at T0, Mr Hamilton recommended Syngenta’s Cherokee fungicide at typical use rates of 1-1.5-litres/ha – containing the two triazoles of cyproconazole and propiconazole, as well as chlorothalonil (CTL). “A triazole alone at T0 may not provide sufficient activity against septoria while chlorothalonil alone is not enough if there is a rust risk,” he claimed.
According to Mr Hamilton, trials in 2015 measured against untreated plots showed a season-long impact with the use of Cherokee in terms of disease control yield benefit (0.8t/ha).
“Trials last year also demonstrated that, when measured as part of a full fungicide programme on a variety with moderate response, a T0 spray can give a yield benefit,” he added.
Looking further ahead to T1, he suggested that a “strong approach” was required to keep leaf 3 clean and prevent inoculum spreading up the plant as a source of infection for leaf 2 and the flag leaf, and this should include a high loading of an SDHI and triazole, and chlorothalonil.
Key requirements for a T1 wheat fungicide
– A High loading of SDHI- Strong protectant activity- Persistent- Control of septoria and rusts- Good compatibility with Bravo (chlorothalonil)