From woodland mushroom … to crop stress relief

Extra effects on top of disease control shown in strobilurin fungicide research

CEREAL farmers who protect crops against diseases using a strobilurin fungicide could be reaping extra gains by helping them fend off damaging stress effects and improving crop greening, according to a programme of over five years of research.

Conducted using the strobilurin azoxystrobin – contained in Amistar and Amistar Opti, and the discovery of which was inspired by naturally-occurring fungicides found in woodland mushrooms – the research has shown additional effects on top of disease control in both field and laboratory tests.

With disease pressures high this season and climate-induced stress often a problem, such combined effects could be particularly useful, experts suggest.

According to Syngenta global researcher Dr Jeremy Godwin, even despite Septoria tritici resistance in wheat, strobilurins continue to boost yield. Indeed, with UK cereal prices having risen from around £60 to £90/t, that extra yield has become even more valuable, he adds.

The typical 0.4 t/ha extra yield seen over the last three seasons from adding Amistar to a triazole fungicide programme has risen from £24 to £36/ha in value, he calculates. While a 0.7 t/ha yield increase from Amistar Opti – which also combines the activity of Bravo against Septoria tritici – has risen from £42 to £63/ha, he adds.

"Clearly, we know Amistar and Amistar Opti boost yield by protecting against key diseases such as rusts, Septoria nodorum, take-all and ear diseases – and these diseases are likely to be important this year. But we also know that crop stress effects are significant," explains Dr Godwin, "for example the link between stresses on barley plants and physiological leaf spotting.

"As well as looking at disease control, these studies also focused on other benefits from strobilurins – in laboratory tests, field trials and even filming differences in how a crop loses its green leaf. Yield isn't just about disease control, it's also about maintaining green leaves to maximise the products of photosynthesis available for grain-filling. Therefore, such information is important for growers' fungicide decisions," he adds.

"We have studied carbon dioxide assimilation – the photosynthetic process which fixes carbon into carbohydrates in the plant. We found carbon dioxide assimilation was increased by Amistar. The benefit of this is more carbon is fixed in the form of carbohydrates which can be stored in grain.

"Equally important, research showed that transpiration or water loss from plants was decreased by Amistar. The benefit is that Amistar allows plants to better tolerate water stress."

To better understand crop greening, Dr Godwin says further research examined biochemical effects inside the leaf. "We found that production of damaging superoxide was reduced following Amistar. This is significant because superoxide is induced by various stress factors and causes leaf senescence. By increasing the activity of enzymes which deactivate superoxide, it appears Amistar helps protect leaves from premature ageing," he adds.

Dr John Reade of Harper Adams University College in Shropshire, who has conducted two years of research into Amistar and Amistar Opti on reducing crop stress, is convinced these are genuine effects.

Examining the impact of stresses caused by reduced light, reduced nutrient availability and drought on spring barley, he looked at the effects of various fungicides when applied to stressed and non-stressed plants during June at T2.

As well as good disease control across both seasons he found stressed plants treated with Amistar and Amistar Opti mixed with a triazole suffered less leaf death or senescence.

By comparison, a triazole alone didn't show reduced senescence, he says. "That's why we can attribute it to a strobilurin effect. This goes alongside disease control, but we feel there's more to it than just disease control," Dr Reade adds.

There was also a trend to plants performing better under drought stress with strobilurins, he notes. But while light stress in particular was found to deplete yield, an extra 0.5 t/ha was achieved following an Amistar Opti plus triazole mixture. Dr Reade believes these results suggest this was due to leaves staying greener for longer where the strobilurin treatment was used.

"If you're looking to maximise yield you've got to keep leaves greener for longer. This allows them to photosynthesise for longer, which allows carbohydrates to be produced which can be exported to the ear.

"If you're carrying out disease control and also giving leaves the ability to maintain photosynthesis for longer, you're going to add to yield effects with strobilurins. I've got no doubt that we're seeing Amistar-related reduced senescence," he adds.

As well as these stress factors, Dr Reade also examined abiotic spotting – known to reduce yield in barley and believed to be due to sudden changes from low sunshine to bright light. "We found that Amistar Opti reduced abiotic spotting, gave good disease control and reduced senescence. That's three ways you can help leaves photosynthesise for longer to push up yields," he points out.

According to Dr Godwin, each additional day of green area in wheat results in 0.15 t/ha extra yield and 0.2 kg/hectolitre extra specific grain weight. Previous university research has shown 3-5 additional days green area after Amistar, versus a standard treatment, he adds.

"This was reinforced by a detailed time-lapse study," explains Dr Godwin, "where the senescence of wheat towards the end of the season was filmed over 15 days which confirmed around a four day extension in crop greening from Amistar."