Oilseed rape growers warned over light leaf spot threat

Oilseed rape growers are being urged not to ignore light leaf spot disease as fungicide control at this stage can lift overall crop yields.

With many rapeseed crops reaching green bud stage in the recent cool and dry weather, crop experts are warning that the disease can still cause major yield losses.

Julie Smith, plant pathologist at crop consultant Adas, says there is still time to use a fungicide at the stem-extension stage, especially if it is one with plant growth regulatory activity.

“Don’t forget about light leaf spot – it is still likely to be out there and good yield responses can be seen from fungicides at the stem-extension stage,” she tell Farmers Weekly.

See also: Oilseed rape growers put on light leaf spot disease alert

She suggests if growers are thinking about a plant growth regulator (PGR) then they should consider one that has fungicidal activity such as the azoles metconazole or tebuconazole.

There is no spray threshold for oilseed rape’s biggest disease threat, but as it can cause yield losses of up to 0.75t/ha, the recommendation is to treat crops when the disease is seen.

If infection is not controlled the disease could cause problems in the following crops. “This year’s innoculm could feed next year’s epidemic,” adds Ms Smith.

Across the country, light leaf spot is being reported even in oilseed rape varieties with good resistance scores to the disease.

A lot of light leaf spot today. Classic symptoms seen in Harper, Picto, DK Exentiel and DK Imperial – all 6 rated. pic.twitter.com/P8uAlw28xD

— Ben Giles (@Gilesy256) March 18, 2016

Light leaf spot still ripping through OSR despite earlier treatment and variety ratings of 7s pic.twitter.com/I6Gvm1S937

— Ben Burrows (@BenBuzzsaw) March 17, 2016

Seeing a lot more LLS now. I think there's going to be some big downgrades in RL ratings this year on certain varieties.

— David Jones (@CCCAgronomy) March 21, 2016