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Light leaf spot (LLS) is being found increasingly readily in oilseed rape crops signalling the time is right to get in with an appropriate fungicide at the first opportunity. That’s the advice of ADAS senior plant pathologist Dr Faye Ritchie. 

With little in the way of winter weather the disease has had little to stop it. “In the past week we’ve seen LLS in early drilled crops, which last had a spray in November. Crops sprayed in December will also be running out of protection, so with no threshold required for spraying crops before stem extension growers need to be thinking about taking action,” she said.

Sodden fields will delay applications, but it will pay to get in as soon as is possible, Dr Ritchie advises. “It is much easier to get good control in crops with low disease, rather than to wait and treat a month later at stem extension when the crop could be heavily infected. Keeping disease out of the upper canopy is the priority, to prevent pods becoming infected as this causes yield loss.”

And she notes that even varieties with a high resistance rating show a good yield response to fungicides, so will be worth spraying. “More resistant varieties can give you more time to get a spray on, but as soon as you’ve seen light leaf spot you need to be thinking about treating, regardless of the resistance rating.”

But Dr Ritchie would hold off with a PGR apart from on particularly advanced crops. “Late green bud/yellow bud is the key time for applying PGRs, and will also provide another opportunity to hit light leaf spot, especially if conditions remain mild,” she notes.

Bayer’s Darren Adkins agrees and says that the last thing growers want is the disease getting into the canopy. “If the disease gets into the canopy you’ll only be able to protect new growth. The danger now is that even autumn treated crops could run out of steam ahead of stem extension. It looks like we could see plenty of the disease again this season and canopies could be at the mercy of rain and wind dispersed spores.

“An application now with a potent LLS product such as prothioconazole would protect current growth, and could be topped up with a growth regulatory and LLS active such as tebuconazole at stem-extension,” he says.