Strong case for three hits to control barley disease

Unlike in wheat, where yield comes mostly from the last three or four leaves to emerge, it’s not possible to link barley output in the same way, says ADAS‘s Jonathan Blake. The crop’s yield seems more associated with components formed earlier.

So promoting early growth to increase tillering and grain numbers per ear in two-row barleys lifts yield potential by boosting storage capacity (the so-called sink size), explains Mr Blake. Indeed a T0 spray has sometimes added 0.8t/ha to the result from a standard T1 and T2 strategy.

“In most cases we expect increased potential to be fulfilled assuming the crop isn’t adversely affected in some other way.” Raising malting barley yields may also improve quality by diluting grain nitrogen.

HGCA/LINK trials controlling rhynchosporium in two-rows from October to January gave, on average, 0.43t/ha extra, even quite low disease levels producing a response.

“Although not tested widely, we suspect the principle of early season crop protection holds true for other diseases. Our work looked at October to January applications, but we expect similar benefits from February to March sprays – before standard T1 and T2 strategies.” Less is known about the responses of six-rows which may behave more like wheat, he believes.

Product choice should be driven by variety and diseases present, he advises. “Applying prothioconazole-based products no more than twice would be best for stewardship.”

Scottish T0 helps keep on top of rhyncho

An early spring fungicide (T0) plus a T1 at GS31-32 will account for 60% of the yield benefit from fungicide, says Simon Oxley of the SAC whose 2004-2007 trials put the average boost from a T0 spray at 0.3t/ha.

“Of greater importance is the fact the T0 enables a grower to keep ahead of disease. Rhyncho is a challenge to eradicate, but relatively straightforward to protect against.”

Applying a T0 allows growers to keep on top of disease at the all-important T1 timing, explains Dr Oxley. “In other words, if the crop is clean at T0, leave it alone as far as fungicide is concerned, but expect 60% of your potential yield to come from a T1 treatment. If you have disease at T0, apply a fungicide so you don’t lose some of that potential.

“We recommend alternatives to the key triazole plus strob mixes at T0. Too much triazole in the programme will increase resistance pressure on that group of fungicides. Using Opus instead of Proline makes no difference, since use of Opus will increase pressure of resistance occurring to Proline. Keep the big gun fungicide products for T1 and T2.”

His T0 advice is Kayak + Torch Extra. “It won’t necessarily be the most effective mix, but there again it’s not the most yield-benefiting timing.”

Use non-azole if T0 required, urges manufacturer

A T0 spray should add to, not replace, the T1, urges Bayer CropScience’s Gareth Bubb. The LINK project shows a T0 can bring benefits but they are inconsistent, he notes. “Don’t cut the T1 rate as it’s still needed to protect the lower leaves.

“It’s really important to get the T1 timing right in barley since the lower leaves – unlike in wheat – are more important for intercepting light after flowering.”

Leaf three emerges around GS31 in barley, says Mr Bubb. “Under high disease pressure delaying the T1 until GS31 compromises control and the protection of leaves four and five. These provide 15% & 16% respectively of the area for photosynthesis compared with 11% from leaf three.”

So T1 in barley should target GS30-31 at a robust rate, as it directly affects grains/sq m, he advises.

The T2 should go on no more than four weeks later, ideally at awns emergence.

“A non-azole T0 approach will help protect against decline in rhyncho sensitivity to azoles and ensure that prothioconazole-based products, such as Fandango which effectively has built-in resistance management, continue to give excellent control.”

More T0 treatments likely, suggests agronomist

Hereford-based AICC member David Lines generally uses a two-spray programme based on Fandango, with the main timing at T1.

“The main benefits are ease of use. Crops have been noticeably clean and greener, and yields have improved. I have used T0s, mainly low rates of Colstar, on varieties with low mildew/rhyncho ratings, but the total spend wasn’t significantly more.

“The timing coincided with early PGR treatment, and though I didn’t see significant yield responses, crops were definitely cleaner.”

Given current cereal prices he expects most of his clients will be prepared to spend rather more on inputs this season. “So I’ll probably use Kayak at 0.5 litres/ha early, which could be early March with PGR, including a specific mildewicide if mildew is present.

“The consensus seems to be that Kayak +/- mildewicide at T0 and then azole/strob at T1 and T2 is the best route.”

More farmers are likely to use three-spray programmes on winter barleys this season, believes Herefordshire agronomist David Lines.

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