Most oilseed rape crops are further behind than in recent years, but using a growth regulator still offers benefits in achieving the right canopy to maximise the number of seeds.

Growers are in a very different situation this spring, says Agrovista technical manager Mark Hemmant. “Crops are much more variable, some are forward and will need holding back while most are backwards.”

There is, therefore, an expectation by many growers that they won’t need to use a growth regulator this season.

“But some of these backward crops are nicely set to produce reasonable yields. How often do you see a poor crop then go on and produce some of your best yields,” says Mr Hemmant.

To maximise yields, crops will need managing to maximise the number of seed/sq m and this requires regulating growth to achieve the ideal plant canopy.

However, manipulating growth to achieve the ideal canopy is set to become easier this season with a new growth regulator. But unlike other growth regulators, BASF’s Caryx has been specifically designed for oilseed rape instead of being an existing cereal fungicide that has had the label extended for use on rape, explains BASF field crops manager Will Reyer.

“In addition, it is the only true growth regulator, rather than being a fungicide that happens to have growth regulatory properties.”

Side branches on oilseed rape plants can contribute as much as 1t/ha to the overall crop yield

It contains the familiar fungicide pgr metconazole (30g/litre) plus the new active mepiquat chloride (210g/litre). “This combination has been widely used on the continent for a few years and is now available for the first time to UK growers.”

Caryx has three key effects on the plant; it helps promote a better canopy, protects against lodging and promotes rooting. It fundamentally manages the use of energy in the plant, changing the hormone balance in two ways, inhibiting gibberellins and stimulating cytokinin production.

Lodging

A key effect of this change in hormone balance is reduced cell elongation, thickening tissue and strengthening the stem. More energy is diverted into rooting resulting in a larger tap root as well more adventitious roots, explains Mr Reyer.

Lodging results in large losses (see panel) and even leaning crops lose yield. According to a recent ADAS report, for every 10% of area lodged, yields fall by 0.07 to 0.16t/ha, depending on time of lodging and the angle from the vertical.

Trials with the new regulator showed that using it at half rate (0.7 litres/ha) reduced lodging from 48% (untreated control) to 12% and applying the full rate of reduced it further to 4%.

Similarly, in several trials carried by ADAS found that applying Caryx resulted in 20% greater height shortening than full-rate metconazole. “The difference was noticeable,” says ADAS principal research consultant Pete Berry.

Canopy

While reducing lodging risk is the traditional reason for using a growth regulator, it also has a crucial role in canopy management. “It reduces apical dominance in the primary stem, reducing overall crop height, and promoting growth and the number of the secondary branches,” says Mr Reyer.

With an overlarge canopy, you get light reflectance (up to 60%) which shades the lower part of the canopy. “Fewer seeds/sq m in the lower canopy equals poor yield,” says Mr Hemmant.

By using the regulator you get an open canopy, stronger lower branches and more light to these lower levels.

“But many growers tend to focus on the terminal raceme and primary branches,” says Mr Hemment.

Finally, using the regulator increases the number of chloroplasts (parts of a cell containing chlorophyll) resulting in increased photosynthesis and delayed senescence, keeping crops greener for longer.

“Compared with straight metconazole, trials show greater consistency, particularly when crops are under stress.”

Reasons for this increased consistency is improved take up of metconazole due to an improved formulation plus the complementary effects of the two actives, says Mr Reyer.

Metconazole has a shorter duration of activity, rapid onset of effects and has an optimum temperature of 12-18C. In contrast, mepiquat has a relatively slower onset of effects, relatively short duration and optimum activity at colder temperatures, says Mr Reyer.

It’s straightforward to use and Dr Berry has carried out nine complex trials to help determine how the product partitions yield in the plant.

“Using the product resulted in a greater number of secondary branches. We measured the contribution and found altogether the secondary branches yielded about 1t/ha. We were surprised they contributed this much.

“The terminal raceme gets most attention, but generally only accounts for 20% of the total. Maximising secondary branching can make a meaningful contribution to overall yield,” says Dr Berry.

Mr Hemmant agrees that this approach to managing canopies delivers more seeds/m sq rather than just lodging control.

With this in mind, Mr Hemmant is looking at combining its use with wide rows. He believes it could increase further the contribution from secondary branches, thus pushing oilseed rape yields even higher.

“We are looking at its use within the Growcrop Gold trials this season and hope to see how it performs in wide row crops.”

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Winter hardiness

On the continent where the winter weather can be much harsher, Caryx is used in the autumn to improve winter hardiness.

“It works by redirecting growth down to the rooting. Leaves are, subsequently, much more prostrate and tighter to the ground, thus helping with winter survival.

“It is currently only approved for spring use in the UK, but we may consider seeking approval for autumn use in the future.”

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Lodging estimate

Last year was a high lodging year, but a new ADAS report suggests growers are underestimating the extent of the problem and more importantly, the cost.

The BASF-funded survey carried out by ADAS used aerial photographs to get a handle on the size of area affected and the severity of damage caused. One of the key findings showed on average 35% of oilseed rape cropping area lodged.

Dr Berry believes the results highlight the need to assess the threat of lodging seriously.

The survey showed over 99% of fields showed some sort of lodging, highlighting the scale of the problem and how much we underestimate it,” he says.

Carried out in 2012, the survey showed that on average, 35% of the oilseed rape cropping area lodged. If the average lodged area of 35% is representative of the whole country, it is estimated that lodging could have reduced the national average yield by between 0.25 and 0.61t/ha.