Springing Ahead

In recent years, far too many crops have gone into winter in reasonable condition, only to be ravaged by cabbage stem flea beetle larvae, pigeons or slugs. Writing-off crops at this stage is especially damaging in wasting the substantial investment already put into them, and in limiting replacement options. Surviving crops tend to be characterised by stunted plants, uneven canopies and flowering, and disappointing yields. Thankfully, the past two seasons have been less problematic in these respects for most. However, the extent of crop losses from pest damage in 2019 and 2020, together with recent very wet and very dry springs have underlined the value of growing varieties better able to tolerate less-than-ideal spring and autumn conditions.

Pennine priorities

At Brignall Farm on the eastern edge of the Pennines near Barnard Castle, Andrew Watson needs his oilseed rape to have plenty of get-up-and-go at all times.

“Running up to 700 ft [altitude], we have to get crops out of the blocks rapidly to keep ahead of flea beetles and pigeons, not to mention the scourge of French partridges when the local shoot is active.

“We want them to be well-rooted with a good big canopy by the end of October. And we like to see them grow away strongly from the winter, though not too early as our clay loam soils take a while to warm-up.

“Excalibur was great for us, DK Exalte even better, and the DK Exstar we have these days is better still. It’s very vigorous without turning into a monster, and it has the best combination of Phoma, light leaf spot resistance and standing power you can get. What’s more, the 25 ha we grew last season averaged 4.7 t/ha.”

Sowing in early August, Mr Watson wants his crops to have plenty of nitrogen in them ahead of spring. As soon as he can travel in February he applies around 75 kg N/ha, which puts enough nutrition in the soil to support the vigorous growth and branching he wants, as soon as crops need it.

Plenty of nitrogen in the canopy and good spring vigour are also important in enabling Mr Watson to delay the remaining 200 kg/ha of nitrogen as late as he can, so as much as possible goes into the seed.

“DK Exstar’s excellent light leaf spot resistance and standing power means we can hold back our stem extension spray too; generally until green bud,” he notes.

“This allows the greatest PGR encouragement of branching, rather than just stem

shortening, and gives a good platform for our flowering spray programme, which is particularly critical with the serious sclerotinia problems we’ve had in the past.”

Lincolnshire learnings

In coastal Lincolnshire, multiple YEN award winning grower Mark Stubbs also grows varieties that “crack-on rapidly” in spring. And he is heartily glad he does, given the intense slug pressure some heavier land at Marshchapel came under last season.

The DK Expectation he grew there proved his star 2022 performer, averaging almost 6 t/ha and delivering up to 7 t/ha over the weighbridge in places, delighting him for its ability to deal with the slug challenge.

“We deliberately chose hybrids when we reintroduced oilseed rape into our rotation just over 10 years ago, and we’ve averaged 4.5 t/ha or more across our farms ever since, starting off with Excalibur, then DK Exclaim, as well as high value HOLL rape.

“We’re not fans of PGRs, so don’t want our crops putting on too much growth ahead of winter. After the Proline they get with Astrokerb in late November, we often don’t spray them again until mid-flowering. So, good light leaf spot resistance and stem strength are vital. “DK Expectation replaced the DK Exclaim that did us proud for many years,” he continues.

“Our best 9 ha field went over the weighbridge at 6.5-7.0 t/ha. But the real proof of the pudding was a large area of one field hammered by slugs that compensated fantastically well to average 4.5 t/ha.

“As it came into the spring we were seriously considering writing the crop off. But there were sufficient plants /m2 for us to give it a chance, and come April, it showed the exceptional vigour we’ve always valued in Dekalb varieties to branch out and fill-in wonderfully well.”

Jim Carswell

Agrii Trials Manager

Agronomic assessments

Spring vigour is a key criterion scored in the field-scale oilseed rape studies Agrii trials manager, Jim Carswell, runs each year, with up to 20 of the most popular and promising varieties on iFarms across northern England and Scotland.

He sees consistent differences between varieties in both the earliness with which they restart growth in spring, and the speed they develop – DK Exsteel and DK Exstar invariably being some of the earliest and fastest respectively.

While the earliest-developing varieties also tend to be the earliest to flower in his experience, this is not always the case. And while he generally favours those that develop fastest, he says some initially slower hybrids can catch-up rapidly, and those later into flowering can perform every bit as well at harvest.

“A good 30% of DK Exstar plants at Bishop Burton were flowering when we scored the iFarm plots on 5 April last year, compared with just 0.5% of the DK Exposé,” he says. “Yet both varieties gave us a very impressive 5.8 t/ha gross output at harvest on 29 July.

“It’s horses for courses. In some cases, rapid spring growth can be a great help in enabling crops to grow away from winter or pest damage. But on cold, wet ground the earliest crops can start growing before the soil warms up enough to meet their nutrient needs. And the more vigorous a variety is in spring, the more important it is to be stiff in the stem.

Earlier flowering can also mean a longer pod fill period for higher yields, although the risk of frost damage is higher, so early flowering varieties need to be particularly strongly branching to compensate for any early pod loss, he says.

Mr Carswell insists growers need to be especially ‘on-the-ball’ with the earliest and fastest developers, both nutritionally and with spray programmes.

“Early nutrition is even more crucial for the earliest starters. Get your first nitrogen and sulphur on as soon as you can travel so they have something to support growth as soon as they need it. Then you can tailor nitrogen to GAI with the second split.

“Fresh available phosphate in spring can be particularly valuable on higher pH soils to combat their tendency to lockup these and other nutrients. And spring applications of the phosphate availability enhancer, Release, have given the most cost-effective responses on high vigour varieties like DK Exsteel in our trials.

“It’s certainly worth considering early foliar nutritional support for varieties with the greatest spring vigour if your soils remain cold and wet too,” Mr Carswell adds.

“As it may also be if the weather turns very dry – with boron especially important to combat stem cracking.

“Good plant growth regulation should be another priority with any particularly vigorous varieties that don’t have the stiffest of stems. They can go into stem extension surprisingly early and the best stem strengthening always comes from an early PGR application.”

Dekalb differences

Clear differences in spring development of leading Dekalb oilseed rape hybrids were again apparent in the 14 field-scale strip trials run by Bayer with growers under their own farm regimes across the country last season.

Earliest to start re-growing in February were DK Extremus, DK Exstar and DK Exsteel. DK Expectation showed a particular turn of stem extension speed to match DK Exstar in its earliness of flowering in April, while DK Excited also picked-up its pace of development to flower ahead of DK Exsteel and DK Exposé.

“Interestingly, when it came to performance, there was little to choose between the varieties,” notes Bayer trials manager, Richard Williams.

“Despite an inevitably earlier harvest than ideal for the later flowerers, variety seed yields were in a tight 4.8-5.1 t/ha range.

“What’s more, the latest flowerer, DK Exposé underlined its developmental flexibility with an above average 5 t/ha. And when harvested a week later than the main strips on one site to replicate commercial practice by better matching its maturity, the variety delivered 5.65 t/ha – 15% up on the average.

“All our work with oilseed rape emphasises the importance of choosing hybrids with the most appropriate spring and autumn development for a farm’s particular conditions, then matching their agronomy to the varieties’ specific strengths,” he concludes.

This article is an extract from CropFocus magazine, if you would like to sign up for the next issue please sign up here