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Don’t forget the fundamentals of fungicides – Agronomist & Arable Farmer – Dick Neale

Although Septoria pressure may be reduced in late-drilled crops, growers should not risk compromising their plans ...

With the unusually wet autumn ruining winter wheat drilling plans, Septoria pressure is expected to be significantly reduced in late-drilled crops. But Hutchinsons technical manager Dick Neale is urging growers not to change disease control fundamentals.

He says fungicide spend can be tailored to meet reduced Septoria pressure, most welcome with yield potential already capped. But he feels a radical shift in fungicide strategies is potentially costly.

“Minimising early season disease control and hoping to rectify matters at T2 is a risky strategy. Last season, after a dry April, we saw a rapid acceleration in Septoria when wet weather arrived. This took many by surprise and something similar could happen this season.”

His view is not to compromise any part of the programme and, while the T2 remains the most responsive timing, he sees the T1 as equally important. “The ultimate aim is flag leaf protection, but the lead into that is the T1 by keeping leaves three and two clean. If you’re still in a protective position by the time T2 comes (GS39) you’ve got flexibility. It’s when you’re chasing disease you have no choice but to opt for the most potent products at higher rates.”

What could impair early season control is the speed of leaf emergence. He expects that as day length and temperatures pick up, crops will respond accordingly. It could make application timing difficult as crops race through growth stages. That isn’t such a concern at GS30 as he questions whether a T0 spray will be needed unless yellow rust pressure is high. But it becomes vitally important at GS32 for protecting leaf three.

“In late-drilled crops, identifying leaf three emergence could be particularly difficult this season. Plants will respond to day length but leaf emergence is driven by thermal time. Leaf three could emerge at GS31 instead of GS32 but we shouldn’t assume it will be earlier, calendar-wise. It could stall if we get another ‘beast from the east’ and for crops that haven’t had a T0 there isn’t much margin for error. Get it wrong and you may not fully protect the leaf 3 so growers will need to be vigilant.”

The speed of crop development could also intensify mildew and yellow rust pressure. “Yellow rust likes backwards plants and adult resistance doesn’t kick in until around GS37. Mildew responds to plant stress and plants short of nutrients, particularly manganese, will be vulnerable,” he warns.

T1 product choices could include azole + CTL when combined with a resilient variety. This provides an opportunity to use a second SDHI fungicide application for the T3, where their disease control and greening properties might help prolong green leaf area.

“With fewer leaves in late drilled crops source capacity is already impaired but can be partially offset by retaining green leaf area. YEN data has shown the value of keeping the top leaves green for longer.”

But active choices should always be driven by disease pressure at the time. He will only hold back an SDHI if he is confident he can keep Septoria at bay through to GS39.”We only have a handful of varieties with the resilience to hang on, with Extase and Theodore being a long way ahead of the rest,” he notes.

With Septoria pressure likely to be at its peak around GS39 an SDHI at T2 is a ‘given’.

He also advises growers not to ‘walk away’ from late drilled crops at this moment. Thousand grain weight could offset fewer ears/m2 and there is the chance to prolong green leaf area. “Typically, we are looking at 8-9t/ha as opposed to 10-11t/ha. Of course, growers need to target inputs accordingly to maintain a level of margin but mustn’t go too far. That will only leave crops open to further losses through disease taking hold,” he concludes.


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