R.M.Jones

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Managing Backward Wheat Crops

Effective spring management will be the difference between success and failure for large areas of winter wheat across the country this season, believes Agrii research and development manager, Colin Lloyd. Management that is designed to address the special needs of late-drilled and late-developing crops under less-than-ideal soil conditions.

From the company’s extensive Throws Farm-based research in previous difficult establishment seasons and under deliberately challenging trial regimes, he identifies three key management priorities – improving rooting, increasing tiller numbers and maximising tiller retention.

“We know sodden ground, difficult seedbeds and high seed rates add up to poor quality rooting, compromising both nutrient uptake and standing ability,” Colin Lloyd points out. “Phosphate access will be particularly problematic in waterlogged soils.

“We also know crops drilled from late November struggle to tiller. And we know they find it harder to retain their tillers when spring and summer conditions get tough, but will do so with sufficient support.
“Thankfully, our R&D shows there’s much we can do to address these particular challenges through the right early season agronomy.

“Back in the poor establishment season of 2007/8, for instance, we found an early March application of the enhanced PGR, Adjust rapidly gave highly significant improvements of up to 35% in average root fresh weight, root plate diameter and root plate length across 17 winter wheat varieties at two seed rates. It also increased the average number of yield-bearing large stems by up to 30%.

“What’s more, the effect persisted through the season. Overall, we recorded a 44% increase in average fresh root weight at early grain fill together with clear improvements in stem wall thickness and both water and nutrient uptake. Despite a complete lack of lodging in the control plots, this resulted in a yield increase of 5% averaged across the varieties, delivering a £65/ha average margin over the input cost with wheat at £150/tonne.”

As an alternative to early Adjust Colin Lloyd recommends Meteor to boost tiller numbers as well as rooting at early-mid tillering. He finds it a more consistent PGR than chlormequat, particularly valuing its ability to suppress apical growth for 25 days (against just seven with CCC) and its greater effectiveness at lower temperatures.

He suggests adding Quark to the Adjust or Meteor application both as a source of nutrients and to encourage tillering by stimulating growth hormone production, together with foliar P, K, manganese, sulphur and magnesium to make-up for any impaired soil uptake.

“Nitrogen won’t stimulate tiller production but sufficient N is essential to retain tillers,” he explains. “With soil N levels likely to be low following the incredibly wet summer, autumn and early winter, I’d be applying a minimum of 50kg N/ha – up to 75 kg/ha on lighter, hungrier ground – as soon as conditions allow"

“While there’s clearly a lower risk of early Septoria in later-drilled crops, rusts and mildew can be bigger problems with softer growth, more rapid leaf development and poor rooting. This is another good reason for keeping Mn levels up both with any early PGR and at T1.

Mildewicides might also been needed ahead of or at T1,” warns Colin Lloyd. “Especially so as we find some varieties may be more susceptible to disease when later drilled than their official ratings suggest.

“To minimise any loss of crop efficiency from disease – including take-all which can be extremely damaging where rooting is already restricted – a strobilurin at GS32 could be valuable in many cases too. In addition to giving the greatest protection to the lower leaves which make a bigger contribution to yield in thinner crops, its ability to improve nitrate reductase activity within the root will assist N uptake.”
Alongside the need for early action to boost rooting and tillering and minimise harmful nutrient and disease stresses, Colin Lloyd stresses that late-developing crops will remain less competitive with weeds for longer than usual. They are also likely to be more susceptible to damage from post-em contact herbicides and spray mixtures.

Under these circumstances, he advises growers to continue using residuals wherever appropriate and not to leave everything until the T1 timing to avoid over-complicated tank mixes.

Recalling aphid damage beyond mid-February in a later drilled crop, he adds that crops remain susceptible to BYDV infection and urges everyone to remain alert to this threat wherever conditions remain mild.

Backward Crop Priorities

  • Do everything possible to encourage and retain tillers by maximising rooting.
  • Apply early N and foliar P, S, Mn and Mg to make-up for soil access difficulties.
  • Employ enhanced PGRs with superior cold weather activity to improve rooting.
  • Target diseases which threaten rooting with morpholine-containing fungicides and
    those with specific persistent mildew activity.
  • Protect lower leaf area and efficiency assiduously with robust early T0 applications.

Remove weeds as soon as practicable to restrict competition and allow free tillering.

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