Early-season sprays can keep mycotoxins in check

Prothioconazole-based fungicide treatments applied either at T1 or at flag leaf can have a significant effect in reducing fusarium infections and mycotoxin loading in wheat grain, according to new research.

In a Harper Adams University College trial, treatments receiving 0.6 litres/ha of Proline at T1 had 15% lower levels of the mycotoxin DON than Opus (0.75 litres/ha). A similar trend, albeit not statistically significant, was also observed when comparing Prosaro against Opus as a flag leaf spray, HAUC researcher Simon Edwards says.

"As far as I'm aware it is the first time anyone has shown a benefit of a foliar fungicide applied before ear sprays."

In an attempt to ensure earlier fusarium infections the trial was inoculated using infected oat grain spread on to the ground in late March, rather than the more normal usual inoculation timing of pre-flowering.

The treatments compared Proline and Opus at T1 and Prosaro and Opus at T2, as well as evaluating a range of T3 options. While every treatment bar a three-spray programme of Opus reduced fusarium infection compared with the untreated, the best control came from T3 applications of prothioconazole, he stresses. "A robust T3 spray is still most important, but the trial showed early sprays could have an impact.

Suppression

But the best programme for reducing DON levels was a T1 Proline followed by Opus at T2, with Proline again at T3, which gave 68% suppression."That's close to the level of suppression I would expect to see in natural situations."

Similar performance from early season prothioconazole sprays was also seen in a Rothamsted Research trial, Nigel Godley, Bayer CropScience's technical manager, says. In that trial Proline was again compared with Opus at T1 and T3, while Prosaro was used to compare flag leaf applications.

As expected T3 Proline gave effective reduction of ear blight, Mr Godley says. "But both T1 and T2 prothioconazole applications also gave a reduction."

He suspects the activity comes from prothioconazole reducing early season inoculum. "It could be from residual activity, but it makes sense the product is reducing sporulation."

Dr Edwards agrees. "I think at T1 it is just general ground inoculum being controlled."

Trash from previous crops is generally seen as a source of fusarium infection. "The big risk is maize, but other crops in the rotation can also be a factor - for example, oilseed rape and wheat," Mr Godley says.

Climate

That could be a reason why there is more fusarium in the east than would be expected given the lack of maize, and generally drier climate, Dr Edwards notes. "I think intensity of rotations could be playing a part. Oilseed rape/wheat rotations, particularly if min-till established, could build up inoculum. Fusarium can grow on any crop debris." Trying to establish the impact of rotations, particularly the intensity of cereals, on fusarium risk is one objective of a HGCA-funded project, he notes.

At T2, prothioconazole could be cleaning up secondary fusarium infections on the flag leaf, Dr Edwards suggests, again reducing inoculum source for ear infections. "We don't know how important that is," he admits.

The use of early season fusarium-active sprays could be important for growers looking to minimise their risk of breaking the EU limits on mycotoxin levels imposed last year, Mr Godley says. "If disease is severe a T3 fungicide might be insufficient on its own to reduce DON - in trials Proline has given around 60-70% reduction in natural situations - so an early season Proline might be an additional useful measure."

Dr Edwards agrees that could be an extra benefit of a T1 spray, but says it should not be the main reason for considering Proline at T1 in most cases. "I wouldn't be putting it on because you get a reduction in ear blight, although anyone who knows they have a specific end use market to protect could consider it."

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