Light leaf spot is now becoming an increasing issue across the whole of the UK
Once a problem for the north and Scotland, light leaf spot is now becoming an increasing issue across the whole of the UK. That’s the view of some technical specialists.
The past two years have seen the spread of light leaf spot (LLS), which has been accelerated by the warmer winters experienced in 2013 and 2014, allowing earlier infection and more rapid recycling of the disease. “In early spring 2014 there was an explosion of light leaf spot following these warm conditions which was a major challenge to control and although this winter has been colder, there has been exceptionally high infection pressure once again,” explains Frontier technical development manager, Stuart Hill.
Andrew Roy, crop protection team leader for the company agrees. “I’ve seen an increase in the level of light leaf spot affecting the 2,200ha of crops that I walk each year. We now find ourselves in a situation where disease incidence is increasing, at the same time as declining fungicide performance with a loss of effectiveness in some of the key triazoles used to control LLS.”
“Because LLS comes into the crop from November onwards, it requires treatment through the winter months, which is a difficult time for spraying especially in the north which is an additional issue to control,” he says.
Spray programmes must become more preventative and use alternative modes of action, adds Stuart Hill. “A combination of SDHI and strobilurin chemistry, is a good option to limit epidemics of the disease.”
Ignoring the problem is not an option as Frontier’s northern seed manager, David Waite, confirms. “Left unchecked LLS can depress yield by more than 1t/ha. Fungicides, of course, can play an important role in controlling the disease but inherent, genetic resistance will give an underlying protection that is invaluable when weather conditions are not favourable to spraying the crop.”
David points out that the next generation of oilseed rape varieties has the potential to raise yields and gross output above the perceived yield plateau. “Care and attention needs to be paid to seedbed conditions and establishment techniques with all varieties. However once the crop is established, disease pressure throughout the winter can test the crop severely; none more than light leaf spot which thrives on the cool damp conditions typical of a normal UK winter.”
All three agree that a critical factor in controlling LLS is the integration of varietal resistance into rape programmes.
Up for recommendation this autumn is the conventional variety, Nikita. Bred by Limagrain, this variety offers a glimmer of hope as it has a LLS rating of 8, which would make it the highest on the HGCA Recommended List. “Varieties with an LLS rating of 8 or 9 show significantly better natural resistance compared with other varieties providing that bit of breathing space required to treat the crops,” says Andrew Roy. “In the past varieties such as Cuillin and Elan were both very strong and it’s great to see some new candidates like Nikita coming forward. These varieties should be selected as an important element in the fight against this very damaging disease.”
Dr Vasilis Gegas, senior oilseed rape breeder with Limagrain, notes that in years when LLS pressure is high, resistance ratings may come under pressure and therefore there’s a distinct advantage in starting with the highest rating possible.
Nikita not only offers a significant step forward for integrated disease management but also delivers solid seed and oil yield. “It’s a conventionally bred variety and a candidate for both the North and the East/West HGCA Recommended List for next year,” continues David Waite.
“In the East/West region, Nikita has a gross output of 110 per cent putting it in joint highest position, 10 per cent above DK Cabernet and 12 per cent over Excalibur, while in the North area it achieves 114 per cent gross output, making it the second best performing variety.
“Additionally it has the short stiff stems that growers prefer for ease of harvest, and very good lodging resistance. Nikita is also medium to flower and mature.”