Once dubbed black gold, oilseed rape as a crop for UK growers now faces a dark future with cabbage stem flea beetle rife in the eastern counties and yield-eroding diseases all too often proving costly to prevent.
The problems the crop is up against are not confined to the UK, however, with pest resistance to pyrethroid chemistry causing similar issues in Germany and more extreme weather patterns playing havoc with growing conditions across the whole of Europe.
With chemicals offering little in the way of effective answers, one German oilseed rape breeder is looking into alternative technical approaches that could reduce yield-loss from pests and diseases, while saving on input costs.
Last year saw a slight decrease in area of oilseed rape grown across Europe, but Alexander Döring, international oilseed rape product manager at DSV, says this is more or less stable year-on-year. By contrast, the rapeseed area planted in the UK last autumn fell by about 14%.
Dr Döring explains that the loss of neonicotinoid seed treatments has greatly impacted European farmers’ ability to grow oilseed rape and predicts that more chemical options may be lost in the next decade or so.
“The number of actives and products available to use in Europe is decreasing in all classes including seed treatments and foliar applications.
“The ban on neonicotinoids is one thing, but the loss of actives will continue.
“It used to take about nine years for the development of a new pesticide, but now 11 years is more realistic and it’s the same for oilseed rape plant breeding too.”
He adds that globally oilseed rape is still viewed as a niche market, which means there is less innovation in herbicides and fungicides available to growers of the crop.
He highlights pyrethroid chemistry, which was considered a milestone development back in the 1980s and is still widely used today, as a prime example.
Add to this the high costs of research and development and rising risks for agrochemical companies in getting their products approved, and it’s clear why chemical options for the crop are dwindling.
More extreme weather as a result of climate change is viewed by DSV as one of the biggest threats to rapeseed yield stability in the future.
Oilseed rape is one of the most drought-tolerant crops thanks to the deep tap root it develops in the autumn, allowing plants to cope in dry conditions.
However, warmer conditions bring heightened risks of certain disease such as verticilium wilt and Dr Döring says breeders will need to work on building varietal resistance in the future.
“Verticilium will increase with climate change and warmer temperatures, overtaking phoma and sclerotinia which will remain at current pressure levels,” he predicts.
“We have to react and adapt our breeding strategy by improving disease resistance for phoma and light leaf spot, but it also be will be extremely important to have solutions to the heightened verticilium risk in future.”
DSV’s senior oilseed rape breeder Detlef Hauska says plant disease resistance will inevitably be a long-term answer to some of the problems growers face, but time is needed for research and development.
“Now we need to have at least a 6 [rating] for light leaf spot and phoma to get on the AHDB Recommended List, so we are focusing on both diseases, but vertilillium is becoming more important for us as breeders.
“The problem with light leaf spot is that symptoms are not always visible and when you can’t see them it makes it hard to select for resistance. Also resistant varieties can become susceptible after a few years as the disease changes.”
Dr Döring stresses that despite the bad news, DSV sees sustained crop profitability in the long term, with an increase in demand for rapeseed oil.
“The importance of the breeder is going to be bigger in the future as other options decline,” he notes.
A look at possible future technical approaches
Alexander Döring says the breeder is investigating how companion crops could be used to help the future of oilseed rape, by possibly saving on herbicide costs and helping reduce pest damage.
“We want to find out how this fits into a normal system because it relies on chemicals to spray it off. There’s also a risk that the companion crop will out compete the oilseed rape plants so we need to find a good species mix.”
So far trials have found that drilling needs happen about 10 days earlier than normal to see any benefit, but doing this risks stem extension before winter, meaning rapeseed varieties with suitable growth characteristics would need to be paired with the companion crops.
He says companion cropping could have the potential to save on herbicide inputs in the autumn by suppressing weeds and this, combined with nitrogen efficiency savings, are estimated to save £80-£120/ha.
“This depends very much on the year and if you need to spray it off. It [companion cropping] could also help with flea beetle control with the use of species which repel the pest and have a masking effect.
“You really have to adapt to make this work and it can be difficult. We need to do more trials and are not at the point of recommendation yet.”
Drop-leg sprayer nozzles
The use of drop-leg sprayer nozzles to apply insecticides to crops is nothing new – the technology is already used for pest control in some vegetable crops.
DSV sees this sprayer technology as a way of reducing the environmental impact of spraying oilseed rape, with the pesticides applied through a 180deg twin flat fan nozzle.
It means growers could use pesticides that they otherwise would not be able to use in flowering rapeseed crops, covering the plant area below the flower without applying any chemical to the flower itself.
In tests this method has successfully applied pesticide to plant area below 70cm and in high disease pressure situations it had a positive yield effect.
This is because the spray is more accurately hitting the right part of the plant, something a conventional sprayer application often fails to achieve.
Dr Döring explains that this technique also reduces spray drift by more than 99% and while the drop-leg nozzles are quite expensive, they might be needed in the future with the introduction of further regulation and restrictions.
Another problem the seed breeder is seeking to address with technical approaches is high levels of crop nitrogen leaching.
One future solution could be to undersow a grass ley to take up N and release it to the following crop, much like a cover crop does.
The undersowing takes place in the spring, with grass seed applied in a mix with farmyard manure or slurry.
“Nitrogen leaching is still a very big challenge facing all farmers. Oilseed rape takes up a lot of N, but it also leaves a lot behind after harvest.
“The grass ley grows very slowly and is left after harvest to help prevent nitrogen leaching,” explains Dr Döring. “It is then sprayed off and ploughed in to release N to following crop.”
He adds that trials are still in their early stages but it is an interesting technique for managing this problems in the future.
Detlef Hauska says all plant breeders are working hard to produce new varieties with better disease resistance, but more can be done moving forward.
In the future plants could be bred to resist and even repel insect attack. For example, he says some insects are put off by hairy leaves and thick waxy layers and oilseed rape plants could be bred with this in mind.
When it comes to pollen beetle attack, Dr Hauska says it could be possible to alter the plant’s flowering time to not coincide with peak pollen beetle migration.
“At the moment the research is still on a basic level and is quite far off. This basic scientific work to find out what part of the plant could be connected to insect resistance,” he says.
He notes that breeders also need to develop varieties which have a greater tolerance of severe damage, coupled with strong vigour to give them the ability to grow back, successfully recover from damage and still give a good yield at harvest.