Important lessons have been learned about cereal disease control following one of the most challenging growing seasons on record, according to one agronomist.

The first of these was that SDHI use proved to be crucial in 2012, especially in a curative septoria situation, said Hutchinson’s technical development director David Ellerton at the company’s winter technical conference, recently held in Peterborough.

“The SDHIs arrived on the market just in time and effectively came to the rescue. The huge yield responses seen to fungicides were largely due to this chemistry.”

However, triazole performance was disappointing in the high disease pressure situations experienced, he acknowledged. “The sensitivity shift to them has continued, so they are now half as effective as they were. It’s becoming more difficult to control septoria effectively with them.”

While the new SDHI chemistry gave better disease control and higher cereal yields, it had to be used at a minimum 75% rate, he continued. “That’s how the best responses were achieved. In some cases, these were as much as 3t/ha.”

SPRING AGRONOMY

The fertiliser spreader, not the sprayer, will be the most useful tool on the farm this spring, Hutchinson’s technical manager Dick Neale told the conference.

“Early nutrition will be needed to promote leaf and tiller growth,” he advised. “Later-sown crops, with fewer, smaller plants and fewer tillers require active management if they are going to fulfil their potential.”

Aim to build 500 stems/sq m by GS30, he continued. “Count your plants in early February. Most crops will need early nitrogen to get them to produce tillers – but remember that nitrogen also needs sulphur and phosphate for best uptake.”

Mr Neale explained that there was the potential for 10 tillers a plant. “A T0 fungicide application will also help the cause, as it will encourage leaf and tiller survival.

For this reason, a triazole is vital. “It influences plant hormone activity. By all means add in some chlorothalonil for its disease protection, but it won’t influence plant growth at all.”

Other lessons included the importance of the early T0 spray for yellow rust control and the impact of including chlorothalonil at T0 and T1 on septoria.

“The T0 proved vital for getting on top of yellow rust. Where it wasn’t applied, or there was a spray miss, the disease was able to cause problems.”

Furthermore, the protectant control provided by chlorothalonil at both T0 and T1 made a difference to the results on septoria, stressed Dr Ellerton. “This isn’t a new finding, but it was essential in 2012. By spraying early and including protectant materials, you avoid getting into a curative situation.”

Fusarium ear blight also caused difficulties, he remarked. “The hot week at the end of May triggered spore release and the subsequent rainfall gave us the highest level of the disease ever recorded.”

All the fungicides used for fusarium control are protectant, he advised, “so they have to be applied early. But even the best chemistry isn’t that great.”

Looking ahead, Dr Ellerton revealed that DuPont’s new SDHI, penthiopyrad (LEM), should be available for the 2013 season. “It gives excellent control of a range of cereal diseases, including very strong protectant and curative control of septoria.

“It also has crop physiology benefits – namely better rooting and more crop greening.”

Four years of ADAS work shows a 0.9t/ha yield benefit from LEM over epoxiconazole, he reported. “There’s even a 3.7% yield benefit from its use in the absence of disease. So it will be a good addition.”

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