Disease ratings in rape varieties may be being undervalued and under-used in selecting cropping regimes for the coming autumn sowing season.

According to Neil Groom, technical director for Grainseed, the ratings in oilseed rape should mean as much as they do in wheat or barley varieties.

“Considering disease ratings in wheat and barley is second nature when choosing which varieties to grow, in rape this appears to be an undervalued benefit," he argued.

"Choosing a cereal variety with a strong disease resistance package can save you money or at least give you more flexibility in terms of widening the spray window. It is the same in rape.”

Last spring – according to Crop Monitor (www.cropmonitor.co.uk) – 91% of rape crops across the UK suffered from phoma leaf spot and 40% of plants within the crop had this disease. This made it the most widespread disease in all regions. “Phoma is probably the most significant and costly disease of rape, causing premature death and yield losses up to 0.5 to 1 t/ha, but there are some varieties with good resistance ratings to this disease.

"Grainseed rape varieties like Mambo, has a rating of 7.8; Alegria 7.4; Decibel CL 8; and Aquarel CL 8. This resistance is also multigene and is resistant to all known strains of phoma stem canker, so is unlikely to break down in the field.

"If you look at the AHDB listing for 2018/2019, there are 20 rape varieties listed and just two have an 8 rating for phoma resistance, two have a 7 rating, three a 6 rating, five a 5 rating, six a 4 rating and two have a poor 3 rating," added Mr Groom. "It has been calculated that each resistance rating point is worth at least £20/ha benefit.”

Light leaf spot is the second most common disease and last spring 2017, it affected 68% of crops and 15% of plants within the crop according to Crop Monitor.

The North showed the highest incidence with 88% of crops infected and 36% of plants. On ratings he added: “A couple of years ago most varieties had a 5 or 6 rating but now many more have a 7. However, 7 is the highest rating out of a 1-9 rating system.

"Mambo has a 6.4 rating for LLS and Aquarel CL a 6, Alegria has a 5.4 and Decibel CL a 5.”

Verticillium wilt has also become more widespread, probably due to it being a soil-borne disease and there are no approved chemical solutions. It can cause heavy yield losses. Growers have to rely on just two control options – growing a resistant variety or widen crop rotations.