T2 wheat treatments merit extra care after tricky spring

Wheat flag leaf sprays look set to be even more important than usual this season, so growers should be especially careful to choose and apply them correctly – ideally, within only three days, urge Syngenta staff.

Given the high cost of inputs, especially fertiliser, getting treatments at this key growth stage right is essential this year to maximise returns and protect producers’ extra investment. But difficult growing conditions so far, with few T0 sprays applied, haven’t helped the decision-making, says the firm’s Rod Burke.

“I reckon the T0 fungicide market is 50-60% back on last year’s, so some growers will have been tempted to spray their T1s early, sometimes before leaf three has emerged. So the gap between T1 and T2 could be longer than usual, and spray timing around GS39-43 will be critical.”

Many crops are thin, backward and poorly tillered after the dry spring restricted N uptake, but they will romp through their growth stages as the weather improves, adds Mr Burke.

That means the lower leaves are likely to add more than usual to yield. “Normally, leaves three and four contribute about 11%. This year it’s more likely to be 17% and you can’t afford to lose green leaf area.”

Delaying the T2 risks severe penalty, he warns. Leaving it a fortnight until GS51 has lopped 0.7t/ha off yield in the firm’s trials.

As usual the main disease target is likely to be Septoria tritici. “There are very few years when it isn’t a problem and it’s there this year. It doesn’t take much for it to turn into an epidemic given the right conditions.”

Controlling brown rust at T2 has been more important in the past two seasons, and yellow rust is already showing up in crops, he notes.

Within that picture Mr Burke advocates a three-pronged risk-minimising approach combining strobilurin, triazole and chlorothalonil for which growers should be prepared to invest £30-35/ha.

The triazole helps cure diseases including septoria, especially important on leaves unprotected by T1 treatments, and the chlorothalonil gives long-lasting protection against less triazole-sensitive strains, he says.

Despite strobilurins being no longer effective against septoria, adding one is well worthwhile at T2, having boosted margins by an average of £37/ha since 2004 through physiological greening and improved rust control, he says.

Syngenta maintains that azoxystrobin – as in Amistar Opti (azoxystrobin + chlorothalonil) – is rate for rate more effective against rust than pyraclostrobin at the low water volumes growers need to consider to ensure timely applications. “It’s more systemic,” says Mr Burke.

Spray retention tests at Jealott’s Hill and field trials show that because of its formulation Amistar Opti is more effective than tank-mixing the equivalent doses of Amistar and Bravo, he adds. “In Opti the Bravo effectively comes free.”

flagleafTom-Robinson

However, product choice should be only half growers’ T2 disease control considerations, says colleague Tom Robinson. Timing and the way fungicides are applied are equally important.

“Delays can cost you 0.5t/ha even in a normal year. Ideally, you need to be able to spray your whole wheat area in three days. If you can’t you should look again at your system.”

Mr Robinson says the once popular two-man bowser back-up system has tended to wane as sprayer tank sizes have increased. But 2007 measurements on one Syngenta Application Club member’s farm showed it could boost daily output by a third.

“A bowser and bowser man will pay for themselves when time is pressing and you stand to lose 0.5t/ha a week.”

For operators continuing to work alone, emptying and rinsing cans can waste valuable time, he adds. Tank-filling measurements on another club member’s farm showed that using a formulated product, such as Amistar Opti, took only half as long as mixing the two components.

Using a lower water volume – say, 100litres/ha, rather than the average 150 – is another way to speed the T2 operation. Angled Amistar nozzles, including the relatively new Go-faster version, permit this without sacrificing crop coverage.

But maintaining the correct boom height, 0.4-0.5m above the crop, is important to maximise spray penetration and minimise drift, stresses Mr Robinson. “Don’t lift it too far.”

Syngenta T2 tips

  • Aim to spray whole are within three days
  • Adopt three-pronged fungicide approach
  • Apply formulated product to save time
  • Reconsider bowser back-up system
  • Use low volume angled nozzles at correct height

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