Striking differences can now be seen between varieties of oilseed rape in terms of branching, flowering and height. Also surprising is the level of Light Leaf Spot that many varieties are starting to show, with a large proportion now with the advanced symptoms of darkened crinkled leaves.
Historically, Light Leaf Spot was referred to as a northern problem and Phoma Stem Canker as the main disease of the South. In recent years however, Light Leaf Spot has developed into a major problem in the south of the United Kingdom with over 90% of crops infected in the South East according to www.cropmonitor.co.uk. The last recorded bad Phoma year was back in 2007 when it had an impacted on yield.
It is up to you to make your own mind up on Phoma, but from the evidence, it could be suggested that seed treatments and Triazole fungicide sprays have kicked it into touch as a yield reducing disease. However, Light Leaf Spot is a different problem. Autumn applied fungicides are far less effective at preventing this disease, achieving at best 50%-80% control. This is a new challenge for the southern farmer to face.
Yield loss from LLS comes from infected plants being killed during the winter, potentially causing 50% yield loss (source HGCA). In the spring, severely affected plants are stunted and produce weak stem extension. Infected stems will display brown lesions and in severe cases, the stems split vertically along the lesion and can break, increasing the lodging risk. These splits can allow access to other diseases such as Botrytis grey mould and Sclerotinia, putting infected plants under an ever increasing pressure.
Growth symptoms can be seen in the spring on leaves, pods and stems. For every 10% of plants infected at growth GS 3.3 (flower buds visible from above ), the Scottish Agricultural College in 2001 estimated there would be a yield loss of 0.14t/ha at £300ex farm which equals £45.99 *.
There are 4 key factors to controlling Light Leaf Spot
Where this disease is more prevalent (Northern region) the HGCA takes this into account for recommendation and will only list a variety that has a 6 rating or higher for Light Leaf Spot. From this we can take that a prudent approach byselecting a variety from the East/West region list, in light of the increased presence of Light Leaf Spot by looking for a variety with a minimum 6 rating.
Incentive a new hybrid from DSV, has an excellent score for LLS resistance, and is also the top yielding variety on both the HGCA North region and the East/West region lists. Combined with its excellent autumn vigour and high resistance to lodging/stem stiffness scores, this variety is the ideal choice for planting in 2014.
*Based on 45% oils, 1% admixture and 8% moisture