Wait until late

13 March 1999


Its time for wheat growers to decide when to kick off with fungicide programmes. Should you start super-early, stick to conventional timings – or leave the sprayer in the shed for another month or so? Gilly Johnson finds out.

The early bird

THERE are at least three good reasons for a prompt start to spraying this season: mildew, yellow rust and septoria. Those crops that were sown early – before rain put a halt to drilling schedules – have raced away in the warm winter, with many approaching stem extension (GS30) by the beginning of March. Such lush young growth could be at risk from overwintered disease well ahead of normal – and these crops are prime candidates for an early treatment.

Spraying at GS30-31 should arguably be termed a T1⁄2 timing, if it is accepted that T1 treatments would normally be applied in the GS32-33 window (between second and third node). Kicking off with a T1⁄2 spray is a strategy more common in Scotland, where slow developing tillers need extra protection.

Where the risk from early mildew and septoria is judged high, then use a cheap and cheerful mix, perhaps applied with the first growth regulator split, just to tide crops over until the standard T1 timing, suggests Dr David Ellerton of ProCam. "Consider a chlorothalonil-type product, or quinoxyfen." He doesnt advise using a T1⁄2 spray, and then waiting until flag leaf (GS39) for the next treatment – "the gap is just too long".

"If the weather allows you to go ahead early, then it could be a good move anyway – bearing in mind what happened last year, when later sprays were delayed."

The other advantage is cost. At earlier timings, effective control of mildew is possible with much reduced rates, adds Colin Myram of the Crop Care Group. "If you get rid of it completely, its much easier, and cheaper, to keep on top of it for the rest of the season."

"The biggest risks this year will be mildew and rust – both yellow and brown," says Mr Myram. "Theres some confusion between the rusts because its hard to distinguish between yellow and brown rust at an early stage. If rusts and mildew are visible, then a spray mid March with spiroxamine or quinoxyfen plus a triazole would be appropriate. This is also part of an anti-resistance strategy."

In most situations, consultant John Clarke of Independent Agronomy wont be straying from the standard T1/T2 type programmes. However, for Brigadier, Savannah, Riband or other wheats which are susceptible to yellow rust he is prepared to go in earlier – "probably with a low rate of Opus, as soon as we see any sign of rust starting to move".

The advisers are agreed that if a T1⁄2 treatment is used, it doesnt mean growers can abandon T1 sprays. Although some adjustment might be made to rate, its best to keep to the T1 timing as a follow up.

In the past, eyespot has been the one disease which has forced sprayers out earlier than T1, usually for a sequence of sprays based on prochloraz products. But with the R strain now predominating, the pressure for very early action has dropped, says Mr Myram – despite what many are predicting will be high eyespot incidence this spring.

The old favourite

CONVENTIONAL timings still rule; most wheat will once again be treated to the familiar T1 (GS32 – second node) and T2 (GS39 – flag leaf) sequence again this year. In practice, that usually means mid-April and mid-May.

Despite initial thoughts that the new chemistry might revolutionise spray timings, and that very early strobilurins (T0 to T1⁄2 )could be used as crop protectants – keeping plants completely clean from day one – two years experience has convinced most advisers that this is the wrong approach. The advice is not to use a strobilurin for a very early spray – instead wait until T1 timings, or later, and then stay with conventional timings.

"Dont leave the gap between T1 and T2 to more than four weeks – even if you use strobilurins," warns Mr Myram. "But if the flag leaf spray is delayed, then up the triazole element to give more kick back."

Many advisers are adopting a sequenced strobilurin programme, with new chemistry included in both the T1 and T2 mix. The T1 spray is now the main focus for eyespot control.

The predominant rye strain can be effectively controlled with a T1 treatment with a number of new products including cyprodinil (Unix) and fluquinconazole plus prochloraz (Foil). Only just released commercially, Foil looks to give reasonable eyespot, good mildew and rust control and excellent septoria activity, says Mr Myram.

"It could be a useful mix partner for the strobs, as it has a Maximiser formulation, which appears to boost the strob effect. We dont have a huge amount of data as yet, but a mix with Amistar seems promising."

A mix of Foil and Unix could be extra effective against eyespot because of the combination of two different modes of action, he suggests.

Another option is Granit (bromuconazole), which gives good control of eyespot as an early T1, together with useful fusarium activity, says Dalgetys Dr Bob Bulmer.

Wait until late

THE waiting game worked last year in Dalgety trials – could it pay off this season? The companys national technical manager Dr Bulmer stresses that a stretched T1/T2 starting at GS33 (third node) followed by a GS59 (full ear emergence) paid dividends, but beware. This was in a season when there was no early mildew, he warns.

Dr Bulmers winning sequence of two full rate Mantra treatments (kresoxim-methyl with epoxiconazole and fenpropimorph) at GS33 and GS59 gave a 4t/ha (1.6t/acre) return as compared with untreated. According to Dr Bulmers calculations, thats a margin over fungicide cost of £234/ha (£95/acre). The success of this strategy depends on maintaining full rates, he says, to ensure any established disease is eliminated by the curative effect of the epoxiconazole element.

Its also important not to open the gap between first and second spray too wide. In the same set of trials, when the T1 went on earlier at GS31 (first node), then the GS59 T2 came in too late to save yield from the effect of disease. Performance fell by 2t/ha (16cwt/acre).

The lesson with later T1 sprays is to judge the season on disease risk and also variety – and adjust rate accordingly. Consultant John Clarke is aiming for a later start on some of the more disease resistant wheats, which then allows the T2 to double up as an ear spray as well.

Dr David Ellerton sounds a warning note. "Waiting till later is a risky approach. If it starts to rain, you could be stuck. In my opinion, GS33 – third node – is too late for a T1."

Prompt action against eyespot

EYESPOT is enemy number one for Cambs grower Chris Ascroft. But he reckons hes found the solution – and upped his yields by over 1t/ha (8cwt/acre) to boot.

Within the 690ha (1,705acres) at Wilbraham Farms, Mr Ascroft has a field of early drilled, continuous Brigadier. With its light shallow soil overlying chalk, this is a prime site for eyespot trouble, and so he doesnt court disaster by delaying a T1 spray.

He aims for a GS32 (second node) timing with the first hit, and so a low rate of cyprodinil (Unix) has been his choice as an eyespot plus foliar product, mixed in with another triazole – usually cyproconazole (Alto).

Last year he split the field in two. Half was given the farms standard T1 mix – low rate Unix with half-rate Alto, which was applied on 20 April when the crop had reached GS32 (second node). Rates of Unix were low; to keep costs down, Mr Ascroft had tended to pare it back to between 0.3-0.5kg/ha.

At the manufacturer Novartis suggestion, Mr Ascroft doubled the rate of Unix on one half of the field, but kept the Alto element. The T2 and T3 sprays (Alto then Amistar) were the same for both sides. That meant the rate of Unix was the only difference between the two. None of the field lodged.

Come harvest, Mr Ascroft was amazed to find a huge yield difference between the two areas. The conventional programme yielded 7.89t/ha (3.2t/acre); the one with the full rate of Unix managed 9.06t/ha (3.7t/acre). After deducting the cost of the product, that worked out as an extra £50/ha (£20/acre) return from the full rate treatment.

Why the difference? Diagnostic assessment indicated a high eyespot risk from both the R and W strains; Mr Ascroft reckons he may have underestimated the effect of the disease on the rooting system in the shallow soil. "I didnt notice much eyespot in the crop – but the diagnostic results show it was there. So well be using it at high rates throughout this spring for our T1 programme, because the numbers speak for themselves."

Thats not the only benefit. Hes looking to extend the window of protection between T1 and T2, to give more room to manoeuvre in case of bad weather. A more robust T1, even at the early timing, might allow this flexibility.

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