Scottish Variety Choice Critical in Light Leaf Spot Fight

That’s the view of Frontier trials manager, Jim Carswell, who suggests that rape is the type of crop where if you get just 1% of the management wrong, then performance can plummet.

He points out that average yields nationwide are no more than 3.5t/ha, yet the genetic potential of rape is certainly double this. 

“Fungicides help to bridge this gap and omitting key sprays, or using inappropriate, reduced rate sprays, coupled with poor variety choice are some of the key limiting factors holding crops back,” he stresses.

In Northern Britain, the key disease remains light leaf spot (LLS) and growers need to do what they can to cut these risks and selecting a variety with the best inherent resistance to the disease is a good starting point.

 “Across most of the UK, we find it is important to get the first fungicide on to coincide with phoma control needs.  Quite often this can be the first week of October, particularly on early-drilled crops - but this is usually 3-4 weeks ahead of any likely need to control LLS.

“However, this means that a second spray – to target LLS – is best left until the weather cools down in November.  At this stage the disease gets into the meristem and, if left unchecked, can cause stunting at stem extension and in severe cases death of the main florets.

“The problem is that at this time of the year, the opportunity to travel and the number of available spray days, are more limited.  This is why varieties with the best 9-rating resistance package – such as Cuillin – are important, particularly the further north you go.”

“Because of its strong disease resistance rating, Cuillin can effectively buy you an extra couple of weeks compared with those rated 7 or less for light leaf spot,” says Mr Carswell.  “This may be just the window of opportunity farmers need to get on and gain control from sprays that can be delayed until mid-November if need be.”

Mr Carswell confirms that Cuillin was a top-performer in Frontier’s trials last year.  However, even Cuillin gave a 15% yield response when a third rate Nov 3rd Proline was upped to half rate.

Looking at season-long rape crop disease control requirements, Mr Carswell suggests that five sprays may be necessary depending on seasonal disease development, varietal susceptibility and growers' aspirations. 

This could start with flusilazole-based fungicides for phoma in the autumn, followed by prothioconazole based products in the autumn, and again in the early spring, for control of light leaf spot.  If a growth regulatory effect is wanted, substitute Prosaro for Proline.

The final two sclerotinia sprays should then be based on Filan and Prosaro – the latter helping top-up and light leaf spot left in plant tissue.  “This is quite a robust programme, but one which helps to minimise the effect of one of the key variables influencing yield,” says Mr Carswell.

Failure to control light leaf spot can cut rape yields by between 0.5-1t/ha and Mr Carswell suggests that by using varieties such as Cuillin to help enable optimum timing of the LLS spray in the autumn, will help minimise these sort of losses,” he says.