Canopy care makes oilseed sense

Article taken from CPM, written by Tom Allen-Stevens

Canopy management in OSR

Agrovista’s Growcrop Gold trials series has helped growers look at the establishment of oilseed rape over the past seven years.  Row widths, seeds per metre row and band application of nutrition and herbicides have all developed in the quest for greater yield.  One problem that has stood o9ut, especially in thick crops is canopy manipulation and plant growth regulation.  Here we look at the latest work to come from the series.

After last year’s sparse offerings, a full oilseed rape crop coming out of the winter may be a cheery site.  But a thick crop won’t yield well unless it’s actively managed, warns Mark Hemmant of Agrovista, and it could end up lodging.

In fact, it’s often the crops that have been knocked back in the spring that go on to perform best – a high-yielding harvest frequently follows a spring drought, for example.  Trials have shown that a crop with the optimum canopy at flowering will outyield one with a large canopy by around 0.4t/ha, or 10%.  So what you do to the crop between now and when flowering starts will determine what yield it’s capable of producing.

Why is a good canopy important?

The driver for yield is seeds/m², but while a full, thick crop will produce plenty of pods, seed production occurs after flowering.  The seed number is actually set by the amount of photosynthesis that takes place in the 2-3 week period following mid flowering, while the amount of sunlight captured for the remainder of the season will determine seed size.

So from the onset of flowering, you have to ensure every green bit of the canopy has access to sunlight to photosynthesise nutrients into yield.  A dense canopy may look as if its intercepting this sunlight, but it results in poor light penetration to lower leaves and pods, while a thick canopy of flowers will reflect light away from green material.

The ideal canopy consists of eight or nine primary branches per plant to achieve optimum seed set, pod fill and yield.  Strong secondary-branch development is also essential.

A population of 25-30 plants/m² in spring will help provide the ideal canopy share – Growcrop Gold trials have found a high seed rate frequently results in a poorer yield.  Row spacing has less influence than overall density, however.  Wider rows (up to 0.5m) achieve the same yield as a standard row width, and in good growing seasons perform better, provided the plant population within the rows is adjusted accordingly.  This is probably down to the way the crops puts out secondary branches to fill the space.

What are the fundamentals?

The optimum canopy to aim for is a green area index (GAI) of 3.5 at flowering.  That actually looks deceptively thin – look down on a crop with the correct canopy and you’ll see about 5-10% of the ground.

Careful management of nitrogen and PGRs is the key to building that canopy and to reduce lodging risk. Unless you’ve an N-Sensor, you’ll need to assess the GAI of the crop before applying inputs.  Digital photographs provide a quick and easy way of estimating GAI, but uploading them to or using BASF’s OSR GAIapp, its Caryx app or Yara’s Image IT app.  Reference pictures are also available on the HGCA website (search for HGCA green area index).

How do you balance N applications?

Unlike cereals, OSR doesn’t transfer resources within the plant.  That means any N in the plant or available in the soil before flowering will contribute to canopy, while N taken up after the onset of flowering will build yield.

Each unit of GAI requires 50kgN/ha, so to achieve the recommended GAI of 3.5 at the beginning of flowering, a 3.5t/ha crop needs 175kgN/ha.

However, plants and soil both contain N, so predicted available amounts must be calculated and deducted from the 175kg/ha requirement – a crop with a GAI of 2 at stem extension will contain 100kgN/ha, for example, and the soil may supply 15kgN/ha (refer to the Fertiliser Manual RB209 or take deep core samples for soil N supply).

The resulting figure should be divided by 0.6 (fertiliser is assumed to be 60% efficient) to obtain the amount of applied N required – 100kgN/ha in this case.  An extra 30kgN/ha for each additional 05t/ha of yield expected (above 3.5t/ha) should be added to the adjusted total to achieve the final target dose of N.

Growcrop Gold trials results suggest putting a little N on early helps get the roots going.  The balance to build the canopy should be applied about two weeks later during stem extension when plants are more likely to use N efficiently, and all crops should also receive 75-100kg/ha of SO₃, ideally with the first dose of N.  Additional N held back for yield should be applied as late as the spreader can run through the crop without causing damage.

What role do fungicides have?

Any crop with a GAI score above 0.8 at early stem extension will benefit from growth regulation – there are few crops this year that don’t warrant treatment.  Fungicides like metconazole or tebuconazole remain valuable, applied at stem extension for best height and lodging reduction and at yellow bud for best canopy manipulation.

But disease control may be the primary driver – light leaf spot is increasing in prevalence, especially in south and east England, and must be seen in the crop, prothioconazole is a better choice at stem extension.

At yellow-bud stage, a strobilurin helps the crop stay healthy and green and provides an insurance against sclerotinia prior to the main mid-flowering spray.  So for forward, thick crops, relying on metconazole or tebuconazole to deliver both growth regulation and disease control may be risky this year.

What is Caryx?

Caryx (metconazole+ mepiquat chloride) is a new PGR, introduced last year by BASF, and the only one available for OSR.  It does the same job as metconazole on its own, and can be applied at the same timings (although only once per season), but our trials have found it’s more effective.

Mepiquat has a slow initial effect of growth regulation, but it’s more prolonged than metconazole.  The actives, combined with the enhanced formulation technology BASF claims Caryx has, means than straight products – if the weather turns against you shortly after application, metconazole can have no PGR effect, whereas Caryx is more reliable.

A low rate of Caryx offers better lodging protection and a similar height reduction to a full rate of Sunorg Pro (metconazole).  Our trials have found it works particularly well at low seed rates in wide rows.

How is it best used?

In the Growcrop Gold trials last year, Caryx was used at three different rates – 0.7 l/ha, 1 l/ha and 1.4 l/ha.

The lowest dose would provide a modest amount of canopy manipulation – this year there are few crops where a higher dose wouldn’t be justified.  So the 1 l/ha application would suit most crops, while for those most prone to lodging, we advise 1.4 l/ha.

Whether this is timed at stem extension or yellow-bud stage will depend on your priority – if lodging is a concern, stem extension is the best timing.  You can always follow at yellow-bud stage with straight metconazole if required.

It’s worth noting the results obtained in the Growcrop Gold trials last year were on crops with a very low level of leaning and lodging.  Weather conditions ensured canopies (or at least those that survived) were relatively sparse.  For 2014, it’s a very different picture, and we’d expect even better results from Caryx across most crops.

Canopy management: top tips

  • Canopy management starts now – most crops will need managing to achieve the maximum potential yield
  • Adjust N applications to suit the canopy – Aim for a GAI of 3.5 at early flowering and work back, taking account of N in the crop and oil
  • Use PGRs where necessary – Most crops warrant an application of Caryx at either stem extension or yellow-bud stage

Sponsors message

The Growers Choice Insite trials programme, conducted by Agrovista UK, lies at the heart of their success in providing the most up-to-date and unbiased technical information possible.

The information is then utilised on farm to maximise gross margins in a consistent, cost-effective and responsible manner.  This in-depth programme is dedicated to finding practical solutions to crop production problems, whether in the broad-acre arable crops or in the pursuit of high-value fruit and vegetable produce.

The Growcrop Gold Oilseed Rape trials series hosts three grower day through the year to look at development work and crop progress.  If you would like more information or to come to any of the events please visit the events page at

To see more of the development work that Agrovista is engaged with, the Select publication is available either through the website or by sending a request for the latest edition to


14 March 2014

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