Early fungicides will play a vital role this year with backward crops needing to retain every tiller that they’ve got to fulfil their potential after a difficult start to the season.

The lessons learned about disease control last year must be put to good use in 2013, believe most agronomists, who caution that smaller canopies in later drilled, backwards crops don’t necessarily mean that disease levels will be lower.

And having seen the value of the SDHIs, the need for multi-site protectants and the importance of triazole dose in the difficult conditions of 2012, there’s every reason to be prepared to make some changes to early fungicide treatments this season, they stress.

At the time of writing, signs of septoria and stem-base browning were evident, while mildew – which is always more of a threat to backwards crops – was anticipated.

In Lincolnshire, higher than expected septoria levels in crops for this time of year could be because many of the wheats are backwards, rather than a legacy from last year, points out independent agronomist Sean Sparling.

“The proportion of leaves with septoria on is greater than usual,” he says. “But there are fewer leaves than we normally see, so it might just be a dilution effect.”

However, the fact that the disease can be found on every leaf means that both the T0 and the T1 sprays will have a job to do, he stresses.

“It’s easy to over-react. But it would be foolish to think that we could get away with a ‘cheap and cheerful’ approach. As well as septoria, there’s plenty of stem-base browning.”

Fortunately, chemistry which is capable of controlling septoria exists in the SDHIs, he continues. “We need to complement and protect them. At the same time, we know that the triazoles are losing the battle.”

That means an Opus/Bravo mix at T1 is no longer good enough, warns Mr Sparling. “There’s a need to change tactic at this timing. Remember if the stem base browning is an eyespot issue, it too has to be controlled by GS32, or you’ve missed the boat.”

He will be trying out Aviator (bixafen + prothioconazole) at T1 this year, as it brings both eyespot and septoria control. The alternative is a boscalid-based product, such as Tracker. “But the 1.5 litre/ha rate of Tracker, which you now need for the extra triazole, is equivalent to the 1 litre/ha rate of Aviator in terms of cost.”

The T0 spray has a different role, he points out. “It does a holding job. It stops any disease that is in the field in its tracks and protects new growth.”

If Mr Sparling finds that T0 sprays get missed, due to workload pressures, he will bring the T1 application forward by seven days. “You can get away with it if the T1 application is spot on. It’s a waste of time putting fungicides on to crops that aren’t growing.”

Mark Hemmant of Agrovista agrees that the T1 choice comes down to either boscalid or prothioconazole. “Provided you are prepared to use more triazole at T1, then you will have both septoria and eyespot covered.

“Doing the right thing for septoria also covers the stem-base browning. Remember that some of the later planted crops have thinner stems, so stem base lesions could have more of an effect.”

Using an SDHI at T1 gives more leeway at T2, he points out. “Plan to have clean crops at T2. That way, if it turns wet, you are still covered. If it’s dry, you can judge the disease risk and amend the programme accordingly.”

The old days of using a half-rate triazole plus chlorothalonil are gone, he adds. “Triazoles need to be used at three-quarters rate, at both T1 and T2.”

The T0 spray, which will be targeted at septoria and mildew, should be a triazole plus chlorothalonil, with some morpholine added to certain varieties and in particular situations, he advises. “We’re not seeing any rust, although this approach will knock back any that is around.”

Mildew can have a detrimental effect on rooting and is more of a problem in backwards crops, notes Mr Hemmant. “There aren’t any spare tillers this year and crops are less vigorous. So their tolerance to these problems is a bit lower.”

He anticipates that T1 sprays will be applied a bit later than normal, towards the end of April. “So the T0s will go on a couple of weeks before that.”

• An additional £150/ha spent on crop inputs compared with 2011
• Increased fungicide spend reflected higher disease year
• Winter wheat averaged 11.64t/ha
• Gross margin of £1,928/ha

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