OSR varieties – Personality over looks

 

For growers sticking with OSR, choosing a variety that has a chance of coping with cabbage stem flea beetle attack is likely to be a key priority. CPM sits down with a breeder, agronomist and seed merchant to gather their views on the varietal characteristics which shift the odds in the crop’s favour.

Establishing the crop using luxury amounts of seed flies in the face of all our previous learnings.

By Lucy de la Pasture

Oilseed rape has always had an element of variability about it, but this year has been a game-changer for many growers who have witnessed crops fail late in spring as cabbage stem flea beetle (CSFB) larval damage finally got the better of them.

“While flea beetle adults may be difficult to control, it’s not impossible. But to cope with larvae, you’re reliant on the physiological response of the plant,” comments Openfield’s Lee Bennett.

The odds were stacked against the OSR crop from the start last autumn, he adds. “The whole flea beetle issue we’re experiencing was exacerbated by the seasonal conditions of last year. Crops went into very dry conditions and many struggled to grow away. After the dry summer the ground had a lot of work to do to re-wet and without moisture, the crop never had much of a chance.”

Although this season has been exceptional for many reasons, there’s no reason to believe the CSFB threat is going to magically disappear. With that in mind, Lee suggests that when growers consider varieties there are more important things than yield to consider.

“Gross output is nice to have but if a variety hasn’t got get up and go, then you risk not having anything. My best advice is to grow hybrids, simple,” he states emphatically.

Peter Cowlrick, independent agronomist at CCC Agronomy and responsible for AICC trials R&D, has also come around to the same opinion.

“Over the years I’ve been cynical of the benefits of hybrids but, on balance, the fields that have suffered the most and been held back the longest are conventional varieties, especially where they’ve also suffered from pigeon damage.

“What’s been very apparent is that it’s the varieties with that extra vigour about them that have coped the best with a high larval load this spring. Often these have also had the Clearfield trait,” he notes.

Hybrids offer more than just hybrid vigour, points out Peter. “Hybrids can be planted at lower seed rates and produce a cotyledon which is about twice the size of one in a conventional variety. That gives plants a bigger solar panel from the word go, so they’re able to put on biomass rapidly and they provide a bigger target to hit with insecticide.

Limagrain’s Vasilis Gegas believes the conversation about how to manage crops to counter CSFB has now come full circle. “There have been a number of tactics employed, including drilling early and increasing the seed rate, but the solution is to start the crop properly. That means selecting the right variety and right seed. By making an investment in hybrid seed, the crop is being given a fighting chance to establish and grow away,” he says.

Before the ban on neonics, OSR husbandry was mostly concerned with how to grow a high-performance crop by obtaining the optimum plant population and managing the crop canopy, points out Lee.

“Nowadays it’s all about establishing the crop by using luxury amounts of seed which flies in the face of all our previous learnings,” he says.

“Increasing the seed rate actually leads to an increase in overall larval numbers per hectare,” adds Peter. “There’s not the dilution effect you may expect.

“Their increased vigour means hybrids can be drilled later, which is a tactic that growers may want to look at this autumn to help reduce the impact of CSFB on crops. Early drilled crops looked good over the winter, but they definitely didn’t grow away as well this spring as later drillings due to higher larval numbers,” he comments.

Although vigour is something that’s much talked about, it’s poorly understood. It’s a phenomenon that hasn’t been quantified and growers only have observational information about varieties to rely on. Even hybrids differ in their vigour, explains Lee.

“Varieties don’t all display vigour twice. Some have get up and go in the autumn and these put on big biomass, while others get going faster in the New Year.

“It appears that if a crop has early spring vigour then it’s more able to bounce back from larval damage and a greater capacity to recover,” says Peter.

Only time will tell if the problems the UK OSR crop has experienced this season is a one off or a warning of things to come, but it’s certainly caused some unexpected performances in the field.

Lee says he’s tracked a variety for a number of years which has looked full of potential.

“This particular variety has vigorous, prostrate growth in the autumn and builds a big canopy. It’s also a later-flowering type and this spring it refused to move during the warm spell we had in Feb because it simply isn’t in its DNA to grow away early. March became cold and was followed by a dry April and hot Easter.

“This variety is now looking disappointing when in the longer term it’s been quite the opposite. It’s not short on vigour but has seasonally been found wanting,” he says.

“We really need to define vigour so that we can quantify it exactly. As we currently understand it, vigour is a combination of biological factors and processes. There are many contributing elements, some which we can measure and others that we can’t,” explains Vasilis.

“In the context of breeding, we separate the different stages of crop development. So when we’re determining biomass this encompasses developmental characteristics such as speed of germination, emergence and establishment.

“To define vigour then we’ll have to tease out these developmental aspects which are genetically determined, giving the variation between cultivars,” he says.

But it’s not as simple as it seems, adds Vasilis. “If a variety has rapid establishment then it’s probably going to be resilient because of its root development, even if the autumn biomass isn’t so good. But a big biomass is also a useful attribute to have because it means there’s nitrogen available to the plant, captured in its canopy. This helps explain why some cultivars are able to get going more quickly in the spring,” he comments.

He also points out that the ability of a cultivar to start growing after the winter is different to the speed it elongates in the spring and this is another factor that can be determined genetically. The way a cultivar behaves before and after the winter is something which he considers breeders need to connect.

Lee agrees that until vigour is truly defined, making a judgement between varieties comes down to what he describes as ‘blonds and brunettes’. “Beauty is in the eye of the beholder. I look at varieties extensively from the time they enter breeders’ nurseries to when they reach trial sites. I see them over and over again, well before any meaningful data even exists. What gets your attention comes down to your own subjectivity.”

Trust between seed merchant and grower is going to play an important role in placing the right OSR variety in the right place this season, and it’s not something Lee takes lightly.

“I’m playing with people’s livelihoods when recommending a variety, but I’ve gained an insight into the personality of a variety over the years I’ve seen it in trials. The AHDB Recommended List (RL) gives numbers but it’s the way a variety behaves that’s most important,” he explains.

In many ways it’s an opportune time to be discussing changes to the way the RL operates, agree all three commentators.

Vasilis explains that under the regulatory system breeders are obliged to score vigour for varieties but because it’s a subjective assessment, it’s deemed the data isn’t reliable enough to avoid misinterpretation so it isn’t published within the RL.

“We need to consider the aspirations of the RL and begin to evaluate the behaviour of OSR varieties in the field, particularly as the goalposts have changed since the ban on neonicotinoid seed treatments,” says Peter.

“The RL will have to change so that it better represents the interests of growers, otherwise it will be of reduced value to them,” adds Lee.

Vasilis believes the discussions about the future direction the RL takes is timely because it’s important to consider how to maintain a reasonable acreage of OSR in the UK, an area that’s widely considered will drop this autumn. He also believes it’s important to maintain a system where trials are robust and supply meaningful, independent data to growers.

“There are some outrageous claims about resilience and vigour of varieties in private trials which is very open to interpretation using data that’s ropey at best. Data from one year from just a couple of sites doesn’t tell the whole story,” he says.

Peter has little doubt that TuYV is playing a contributory part to poor crop performance this spring and is a disease that can creep under the radar.

“In our area, crops tested in Feb had 80-100% TuYV infection, even in crops treated with two well-timed systemic insecticides based on good crop scouting. OSR varieties with resistance to TuYV seem to have grown away much better from larval damage than crops that are under a combined stress,” he notes.

In a Limagrain survey carried out last autumn, TuYV infection levels were much higher than in previous seasons, where it normally sits around the 30-40% mark, says Vasilis. In 2018 the South East and East Midlands proved to be TUYV hotspots but it’s endemic across the whole of the UK.

Lee believes planting a variety with resistance to TuYV is a no-brainer. “Genetic resistance is there and it’s robust so we should use it, otherwise it flies in the face of everything that’s deemed important in IPM.

“Last autumn I saw OSR which established alright but struggled with adult flea beetle feeding in the dry conditions. The grower sprayed it with three pyrethroids, which did a sufficient job to stem the flea beetle enough for the crop to grow away but it also killed all the predators. He then had to apply a foliar neonic to control aphids – his crop tested 85% for TUYV. It’s crazy to use foliar insecticides when you can use genetics at no extra cost, in fact it’s probably a cost-saving to invest in genetic resistance,” he comments.

Peter agrees that as an industry IPM tools need to be adopted more widely, pointing out that in Lee’s example the cost of using foliar neonics would be in the region of £30/ha, which would more than pay for the extra cost of hybrid seed with the TuYV trait.

The fact there’s no yield penalty associated with the TuYV resistance is another good reason to make use of the trait, says Vasilis.

Choosing a variety that has a combination of traits and characteristics that help the grower overcome agronomic problems is undoubtedly a part of the solution, but Peter highlights seedbed preparations as also crucial in the battle against flea beetle.

“A key point is to avoid creating flea beetle friendly seedbeds. That means timely preparations and make sure seedbeds are fine and firm, double rolling if necessary.

Vasilis agrees, suggesting growers throw the calendar out of the window and rely on drilling their OSR only when ground conditions are suitable to give the crop the best chance of establishment. The genetic solution to the CSFB problem is a number of years away, he believes, partly because it’s very difficult to produce reliable trials data for tolerance to pests because of their sporadic nature. But the answer could be a lot closer if the EU were to embrace breeding technologies such as gene editing.

“The EU decision against new technologies was a kick in the teeth to breeders. With gene editing we would be able to incorporate pest tolerance much more quickly. Using classical breeding tools it will be a long time before we can find a trait to introduce,” he says.

More investigation needed to confirm field observations

Pioneer Hi-Bred’s Andy Stainthorpe believes the industry has been caught by surprise after the neonic ban. “The neonics nailed the CSFB problem but the difficulty with an effective chemical control is that it becomes a crutch. When you take the crutch away then there’s nothing to fall back on as no one had to think about alternative strategies to control flea beetle.”

That means growers and agronomists are having to work out an IPM strategy as they go along using a trial and error approach, he says. “The research simply hasn’t been done to show which strategies growers can adopt that will work.”

This also applies to the attributes of different varieties and what it is about them that may be beneficial in a flea beetle situation, adds Andy. “The observations from the field this spring are really interesting, but we need more research to establish what they actually mean.”

He uses the observation that varieties with the Clearfield trait seem to have coped better this spring as an example. “It’s possible to theorise why this may happen. It could be that if you have a Clearfield hybrid then you’re able to take out more brassica weeds and volunteer OSR, so removing some of the host plants.

“Until proper work is done, we don’t know if this happens or there’s something else at play. In the meantime it’s important not to draw too many conclusions from observations this season, even if there’s logic to them, because we don’t know if they’re repeatable or can be relied upon,” he comments.

In the autumn, Andy points out time of drilling has a bigger effect on canopy development than the difference in vigour between different hybrids, but there can be much bigger vigour differences between varieties in the spring.

Different growth habits may also play a part in how well an OSR plant can withstand larval damage and this warrants further investigation, he suggests. “Semi-dwarf varieties have better winter hardiness because their growing point is situated very low down. This could help mitigate damage and their capacity for branching may be another useful attribute to help withstand high larval infestations.”