Record levels of light leaf spot found in oilseed rape

Oilseed rape growers are advised to check crops for light leaf spot (LLS), as severe outbreaks are being found throughout the country, threatening yields.

LLS thrives in the moist, cool conditions seen in recent months and if left untreated, could result in yield losses of up to 1t/ha.

Mark Bollebakker, senior field trials manager at AHDB, has seen record levels of LLS in Recommended List trials.

See also: Should growers persevere with oilseed rape despite challenges?

“Farmers should be wary of this outbreak as it could potentially have an impact on yields – unless carefully managed through use of fungicides over the next couple of weeks.

Mark adds: “The biggest risk now is if the infection gets onto the pods, which can cause them to become brittle and thereby shed their seed prematurely before the harvest.”

The disease is caused by a fungus and appears as small brown or light green spots on the leaves of plants, with a “fag-ash” appearance.

Paul Gosling, AHDB senior crop production systems scientist, explains that the fungus overwinters on crop residue and can be spread quickly through rain splash and wind, as well as via contaminated machinery.

“Once the fungus infects a plant, it can quickly spread throughout the entire crop if left untreated.”

AHDB crop trials have shown fungicides such as prothioconazole, tebuconazole and mixes containing prothioconazole are effective against LLS.

Growers will have used many of these actives in their spray applications to prevent sclerotinia.

Cultural controls for light leaf spot 

  • Cultivate/plough oilseed rape stubbles to bury infected crop debris
  • Widen the rotation between susceptible crops.
  • Grow new crops as far as possible from old crop fields
  • Drill later, especially in high-risk situations.
  • Avoid saving seed from heavily infected crops
  • Grow a variety with a resistance level of 6 or above.

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