New researchat Scotlands Rural College is seeking to discover better ways to predict anoutbreak of light leaf spot in oilseed rape crops. Light leaf spot is thenumber one disease threat to oilseed rape crops and can cut yields by up to atonne per hectare. SRUC researchers will also look to pin down the best timingsand treatments to manage this perennially tricky problem. The 114,000 projectis funded by industry body HGCA. It will be run by SRUC in conjunction withWeather Stations, Rothamsted Research and ADAS, in order to study the spread ofthe disease over a range of sites and varieties.
In 2005 justover 20 million of oilseed rape in the UK was lost due to LLS; in 2012 thatfigure was over 150 million. Like many pathogens Leaf Spot evolves constantlyto try and get around the defences thrown at it. Typically it will erodebetween half a tonne and a tonne of yield from an infected crop. It was onceconsidered a northern UK disease but has spread south in the last two seasonsso that the SRUC crop clinic in Edinburgh has been inundated with requests toconfirm the symptoms at sites right down to the south coast.
FionaBurnett, SRUCs Crop Protection Team Leader, says: With light leaf spot nowmaking its presence felt both south and north of the border this research willbe fundamental to enhancing growing conditions for farmers. After the projectwe should be able to predict possible epidemics of the disease and improve ourguidance around timing of fungicide use.
Trial plotshave been established in three sites in England. In Scotland SRUC will bemonitoring two sites close to Edinburgh and Aberdeen. Researchers willtherefore be able to assess a range of types and varieties, with differentlevels of resistance at different geographic locations, over the course of thethree year project.
While theresearch could help farmers better predict epidemics and better target theirprotection strategies Fiona is warning that, in the meantime, farmers shouldnot become complacent.. While it looks like this year could see a lower LLSlevel than usual, the incidence of the disease has shot up in the last decade asestablished varieties have declined in resistance to this very variablepathogen, something one good year will not change.
Preventionand treatment of Light Leaf Spot relies on resistant varieties, however,inevitably the disease has adapted and varieties like Cracker which were rateda nine when first introduced have now been downgraded to an eight and at somesites behave more poorly than that.
The otherkey defence against the disease is fungicides, but some are now proving lesseffective against the disease than previously. Sensitivity to some of the olderfungicides has declined and there are often quite large differences insensitivity between sites and between seasons. A further difficulty is thatoilseed rape is very vulnerable to the stressful effects of some fungicides.This effect can be useful to regulate the growth but in a stressed crop theeffect of growth regulation can often be negative to yield.
According toFiona: This year, with so many crops early drilled in fine conditions, growthstages are very advanced and a decision might be made in the spring to slow thegrowth of the crop using a treatment such as tebuconazole. However, growershave to be careful as too much could be detrimental to the crop in the longterm. This makes decisions about using chemicals very hard as they need toprotect the crop and check its growth without damaging it. We hope thisresearch will make such decisions easier and so reduce yield loss in the longterm.