GROWERS are being urged to heed the warnings of high levels of light leaf spot in oilseed rape, when choosing their next variety to sow.

The wet weather has provided ideal conditions for LLS to flourish in winter crops as the disease is spread by rain splashes, and as LLS comes into the crop from November onwards, it requires treatment into the spring months.

However, this year some missed their autumn sprays, normally targeted against phoma but with an effect against LLS.

Therefore, the implications of high infection levels for next season’s crops are considerable, as the fungus which causes LLS can continue to cycle in the crop for an entire season if weather conditions are conducive. The fungus survives on debris after harvest and is ready to infect nearby crops emerging in the autumn.

Growers are being urged to consider the role genetics can play in helping to defend against the disease which is equated to the 'septoria tritici of oilseed rape’ and which experts believe costs growers £140m a year in lost yields.

“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, or the disease is not spotted,” pointed out Agrii’s technical seed manager, David Leaper.

“Last year, we didn’t see such an impact on yield from LLS in England in spite of seeing significant disease in crops in early spring. In 2015, February and March were cold and dry, so leaves tended to drop off and the levels of infection were reduced.

"This year with a cold, wet spring, plants have held onto their leaves and it has been easier to see the symptoms develop and get progressively worse.”

ADAS’ plant pathology researcher, Julie Smith, added: “We have seen big yield losses from LLS in recent year’s particularly when fields have been too wet to travel and fungicide timings have slipped. Even the strongest products will not perform well in highly curative situations so it’s important not to let the disease become established early on.”

“As a rule of thumb, 15% plants affected at stem extension equates to a 5% yield loss and I saw commercial crops in the spring which were close to 50% affected.

"LLS will cycle approximately every 4-6 weeks and the wet weather has helped splash spores around and enabled the fungus to progress up the canopy."

With conditions this winter and spring looking suited to the spread of the disease, Mr Leaper expected to see high infections levels across the Agrii WOSR national trials sites, but they have been much higher than he expected.

He said that at the end of March, early April, plots across all of its sites were scored for LLS infection on a rating of 1-9 (with 1 being no infection and 9 being severe).

“The results have been alarming, as there were only four varieties that showed up to or less than 2.5 % infection – the conventional variety, Nikita, stood out with one of the lowest infection levels at 2.3%, taking into account both treated and untreated results.

“Looking at this in more detail in two trial sites, only 1% of plants were infected and this only went up to 3% of plants infected on the untreated plots, clearly demonstrating the robustness of Nikita’s 7 for LLS resistance.”

“Interestingly, varieties with a resistance rating just one lower than Nikita’s did not perform nearly as well. For example, Campus, which is rated a 6 for LLS on the RL showed 6% infection in the untreated and 5% in the treated.

"Nikita missed out being recommended for the East/West list last year on the basis of its lower phoma rating. While this was disappointing, we know that in an open autumn a vigorous variety like Nikita will grow quickly," added Mr Leaper.

“It’s certainly worth considering this wherever you are in the country when planning variety choice for next year as infection levels look high and autumn conditions are always uncertain for spraying.”.

Dr Vasilis Gegas, the senior oilseed rape breeder with Limagrain, said that in years when LLS pressure is high, resistance ratings come under pressure and that there’s a distinct advantage in starting with the highest rating possible.

“There have been considerable advances in varietal defence to LLS in the last five years and one of the reasons for this comes down to the fact that, with increasing levels of infection year on year, breeders have been able to make better selections and that is why we are seeing varieties with better LLS resistance," he argued.

"There are some excellent new varieties coming through and we must start using them if we are to achieve robust disease control whilst minimising the drive toward fungicide insensitivity.”

Nikita has a high gross output of 108 % in the East/West and comparable to Campus in the north, at 110% of controls.