Free disease diagnosis is on offer this autumn to identify oilseed rape’s most damaging disease, light leaf spot, which can halve crop yields if left unchecked.

This aim is to help to spot one of the most difficult diseases to detect in its early stages during the late autumn and winter, and decide on appropriate fungicide treatments.

The disease clinic is being initiated and funded by agrochemicals group Bayer, with crop consultant Adas undertaking the diagnosis, and the aim is to try to get results back to growers within a week of Adas receiving the sample.

The project kicks off on 1 October and will run until March, with pre-paid envelopes being supplied to growers, and Adas preparing to test 500 leaf samples throughout the monitoring period.

See also: Wet weather prompts phoma disease alert for oilseed rape

Light leaf spot is the most yield-sapping OSR disease, and is spreading in importance, as growers are sometimes not recognising the symptoms quickly because it can be difficult to see in its early stages. It is often confused with scorch from fertiliser or herbicides.

Early disease warning

Julie Smith, plant pathologist with Adas, is leading the scheme and points out that disease symptoms are not usually seen until mid- to late November, but can appear as late as mid-January, so some early disease warning will be helpful.

© David Jones

“Light leaf spot is an important disease that is often misdiagnosed or not spotted early enough to allow effective fungicide treatment,” she told Farmers Weekly.

Samples will be examined for a range of diseases including phoma, alternaria and downy mildew, but the focus will be on light leaf spot, which can be hidden and take several weeks from infection to symptoms showing.

Initial infection occurs via airborne spores that are released from last year’s oilseed rape stubbles. Predicting when to use a fungicide, which gives about three weeks of disease protection, can be tricky

Claire Matthewman, Bayer’s oilseed rape fungicide specialist, said the aim is to help growers and agronomists to get a better handle on the disease, with the scheme entitled SpotCheck.

“We hope this will provide another tool in the armoury to gain a better understand of this oilseed rape disease,” she said.

Target pesticides

Sean Sparling, chairman of the Association of Independent Crop Consultants, is supporting the scheme because he believes it is important to target pesticide inputs effectively.

“It is key that we understand where disease levels are, as it is vital we target inputs as precisely as we can,” he said.

Growers are advised to contact Adas for pre-paid envelopes, and then pick 30 random leaves and send them to an Adas laboratory.

Growers should provide a selection of large and small leaves, as light leaf spot can often develop first on newer leaves and phoma on older leaves.

Many growers already select leaves, place them in a plastic bag and leave in a warm room so the disease develops in a few days, but this laboratory analysis will give a more accurate disease diagnosis.