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Wed 20 Feb 2009
Source: Farmers Guardian [edited]
<http://www.farmersguardian.com/story.asp?sectioncode=19&storycode=24447>

Light leaf spot levels highest since 1995

Light leaf spot in oilseed rape is at its highest level since the epidemic of 1995 a Defra [Department for Environment, Food and Rural Affairs]-funded survey of commercial oilseed rape crops has revealed.

In autumn 2008 light leaf spot affected 9 percent of crops and 1.8 percent of plants (compared with 12.2 percent of crops and 1.7 percent of plants in 1995). Incidence of the disease last autumn [2008] was also markedly higher than the long-term mean. Crops in the south east have been affected at this growth stage for the 1st time since 1997.

Regional analysis confirms trends noted in previous years with the highest incidence of disease recorded in the north and some in the West Midlands, says the Central Science Laboratory [DEFRA], which conducted the survey as part of its Crop Monitor service.

Growers are advised that as light leaf spot remains active at very low temperatures, the cold weather could lead to more damaging attacks of the disease than usual. Fungicide use last autumn [2008] was low because of the later sowing and the slow development of phoma leaf spot.

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[Light leaf spot (LLS) of _Brassica_ species is caused by the fungus _Pyrenopeziza brassicae_. In the UK, it has been reported to cause considerable yield losses of oilseed rape (_Brassica napus_) of up to
1.5 t/ha estimated at [GBP] 40 million [approx. USD 57 million] per year.

Leaves become infected soon after sowing, but remain symptomless until lesions appear on older leaves. Developing pods are often infected, leading to premature ripening of seed and pod shatter. LLS is polycyclic and survives the summer on crop debris, volunteer oilseed rape, and vegetable brassicas. Disease management includes varieties with decreased levels of susceptibility, disease monitoring, and timely fungicide applications.

Phoma leaf spot and stem canker (blackleg) is caused by the fungus _Leptosphaeria maculans_. For more information see link below.

Maps of the UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/promed/en?v=53.167,-0.25,5>

Pictures of LLS symptoms on oilseed rape
Leaves:
<http://cropmonitor.csl.gov.uk/wosr/encyclopaedia/view_iImage.cfm?id=46>  and <http://www.sac.ac.uk/mainrep/images/winteroilseedrape?view=Standard>
Pods:
<http://www.rothamsted.ac.uk/ppi/pics/llsp_lge.jpg>

Links
Information on LLS on oilseed rape:
<http://www.sac.ac.uk/consultancy/services/c-e/cropclinic/clinic/diseases/LLS>,
<http://www.rothamsted.ac.uk/ppi/ppigallery.html#lls>,  and
<http://www.niab.com/services/disease/resistance-pathogen-characterisation/pyrenopeziza-brassicae.html>
LLS epidemiology:
<http://www.rothamsted.ac.uk/ppi/diseases/lls.html>  and  <http://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO.2003.93.6.657>
_Pyrenopeziza brassicae_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=322140>
Information on phoma leaf spot:
<http://www.cropmonitor.co.uk/wosr/encyclopaedia/downloadfile.cfm?id=1428>
Central Science Laboratory:
<http://www.csl.gov.uk/>.  - Mod.DHA]

[see also in the archive:
2008
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Fungal diseases, wheat, oilseed rape - UK 20080930.3083 Light leaf spot, oilseed rape - Ireland, UK 20080403.1225
2007
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Foliar diseases, brassica crops - UK 20070913.3037]