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Growers with early sown OSR and higher levels of light leaf spot in OSR varieties, will require treatment this spring, says the nationwide SpotCheck service. The service is a collaboration of Bayer, ADAS and the Association of Independent Crop Consultants (AICC), which offers a free laboratory service. The service analysed samples from 200 crops of OSR and more than 40 different varieties, sown from late July to early September, and diagnosed infections before symptoms developed.

Infection rates have climbed from an average of 5% before Christmas, to 29% in January and February, to over half of the samples showing leaf infection rates of more than 10% and over a quarter 50% in 2022.

SpotCheck Light Leaf Spot has average infection rates noticeably higher in varieties with light leaf spot resistance scores of less than 7.0 and in crops sown before August 21, with Dekalb Ex hybrids showing particularly low rates.

Rosalind Martin, SpotCheck co-ordinator, Bayer says, “Our January & February samples show over three quarters of all crops are going into the spring carrying light leaf spot infections, and this rises to nearly 85% from earlier sowings.”

This shows sowing date and genetic resistance combine to affect the crop, varieties with less-than-ideal resistance are showing infection rates of almost double those with strong resistance from earlier sowings this season.

Rosalind Martin says, “With infections set to cycle increasingly as the weather warms, it will be more essential than ever to keep on top of this damaging disease with a robust fungicide programme from early stem extension through to flowering. A large proportion of this season’s crop were sown relatively early; most crops are coming out of the winter with strong potential and November rapeseed values at record levels. As light leaf spot infections become established well before they become evident, it’s important not to wait for classic leaf-spotting symptoms before spraying,” she adds.

To access the service, Rosalind Martin says “All you need to do is request a sample pack through our website, send your samples direct to ADAS and you will be e-mailed the results within seven working days of their arrival at the laboratory. It’s as simple as that and completely free.”