Utilise variety resistance to combat light leaf spot
Stable domestic demand and a fall in the crop area are helping to keep oilseed rape values above their five-year average. For many growers, oilseed rape remains the most profitable and convenient break-crop option.† Unfortunately, it is not without its challenges.
One of the key threats to profitability is disease, specifically light leaf spot with data from Crop Monitor highlighting the escalating cost. Between 2005 and 2014 (the latest period for which data is available) the impact of light leaf spot to growers in terms of lost output is reckoned to have increased seven-fold to more than £140m a year. No other disease has had such an impact on the performance of oilseed rape.
There are several reasons for this escalation, such as:
- the increased frequency of oilseed rape in the rotation and the popularity of low- or no-tillage cultivations, both of which have led to more inoculum being present to spread infection;
- the popularity of varieties with poor resistance;
- the falling performance of fungicides used to control the disease; and
- difficulty in keeping the crop free of disease before stem extension occurs as ground conditions through the winter can make application a challenge.
The weather too plays a part of course, and it is not always possible to apply fungicides before disease takes hold. Nonetheless, growers do not have to rely solely on the weather; there is another way to approach the problem. Variety choice is the obvious starting point.
A recent report from AHDB advocates greater use of those varieties with better disease resistance, specifically those with a score of 6 or above.
Its sage advice and adopting it is easier than many realise. Some recent variety introductions combine high yields and excellent disease resistance to both light leaf spot and phoma stem canker.
An example of a high yielding variety with excellent disease resistance is Butterfly, a candidate variety from KWS for consideration for addition to the Recommended List in 2018 and available to growers this summer.
Butterfly is an excellent variety with UK-wide potential. It combines high yields with excellent standing and stem stiffness with outstanding light leaf spot and phoma stem canker resistance for which it scores a 7 to both.
above: Chart 1; LLS impact on yield
With light leaf spot now a truly national disease, KWS investigated its impact on yield and the significance of the December fungicide timing by comparing a variety rate 7 for LLS with a significantly lower scoring variety rated 4. Chart 1 gives the results.
The results demonstrate the importance of keeping the crop disease-free ahead of stem extension to protect yield. In practice however, it is not always possible to apply fungicides when they are most needed. Just as with cereal crops, oilseed rape varieties with better disease resistance show greater resilience under pressure thereby affording the grower an element of yield security.
Given the reduced efficacy of the chemical control of the disease and the current value of the crop it is crucial that growers use every available tool to protect their gross margins.† A logical place to start is with using a variety with improved resistance to light leaf spot, such as Butterfly, to reduce the risk of yield loss.