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[1] Light leaf spot - Ireland:
increase
[2] Light leaf spot - United Kingdom: alert
[1] Light leaf spot - Ireland: increase
Date: Tue 1 Apr 2008
Source: The Independent [edited]
<http://www.independent.ie/farming/crops-pinpoint-the-growth-of-crops-1333778.html>
Oilseed rape is now starting to flower in all but the later-sown
or backward crops. Walking through a few crops last week, I was
surprised to find that the incidence of light leaf spot had
risen to alarming levels compared to a relatively clean crop a
couple of weeks ago.
The symptoms from the disease look a little like fertiliser
damage and, where the infection is particularly bad on the leaf,
it will take on quite a curled up look. Immediate action is
needed where the disease reaches this level. Research has shown
that, where 25 per cent or more of plants are affected, control
is economically viable, with an application of a fungicide.
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[2] Light leaf spot - United Kingdom: alert
Date: Tue 1 Apr 2008
Source: Crop Monitor UK [edited]
<http://cropmonitor.csl.gov.uk/wosr/encyclopaedia/view_icard.cfm?cslref=12680>
The spring survey of commercially grown winter oilseed rape is
currently underway, and most of the crops have now been assessed
for disease.
Provisional results show that light leaf spot levels and
severity are higher than in recent years. 65 per cent of crops
assessed were affected.
The highest incidence has been found in samples from the north
and the south west.
See the light leaf spot forecast for details of risk in
different regions at <http://www3.rothamsted.bbsrc.ac.uk/leafspot/forecast/Default2.htm>.
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[Light leaf spot (LLS) in _Brassica_ spp. is caused by the
fungus _Pyrenopeziza brassicae_. In the UK, it has been reported
to cause yield losses of oilseed rape of up to 1.5 t/ha, at an
estimated cost of more than GBP 30 million (USD about 59.4
million). It is rarely very damaging on other brassicas. Leaves
become infected soon after sowing, but remain symptomless until
pale green or water soaked lesions which are brittle and crack
easily, appear on older leaves. LLS can cause severe damage if
it attacks the flower buds before stem extension and can cause
the buds to rot. Developing pods are often infected, leading to
premature ripening of seed pods and pod shatter.
LLS is a polycyclic disease. The fungus survives the summer on
debris from the previous crop and to a lesser extent on
volunteer and vegetable brassicas. Crop infection is initiated
by wind-blown sexual spores in the autumn and develops through
subsequent cycles caused by rain-splashed asexual spores
resulting in characteristic patches of disease by spring. It is
thought that a 2nd sexual cycle takes place on decaying plant
material releasing a 2nd flush of spores. Disease management
includes use of varieties with decreased levels of
susceptibility to LLS, disease monitoring, and timely
applications of fungicides.
Maps
Ireland:
<http://www.fishing-ireland.de/karte.html>
and <http://healthmap.org/promed?v=53.2,-8.2,5>
UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>
and <http://healthmap.org/promed?v=54.5,-2,5>
Pictures of LLS symptoms on oilseed rape:
<http://cropmonitor.csl.gov.uk/wosr/encyclopaedia/view_iImage.cfm?id=46>
and <http://www.sac.ac.uk/mainrep/images/winteroilseedrape?view=Standard>
(leaves) <http://www.rothamsted.ac.uk/ppi/pics/llsp_lge.jpg>
(pods) Links Information on LLS on oilseed rape:
<http://www.rothamsted.ac.uk/ppi/ppigallery.html#lls>
and <http://www.sac.ac.uk/consultancy/cropclinic/clinic/diseases/LLS>
LLS epidemiology:
<http://www.rothamsted.ac.uk/ppi/diseases/lls.html>
_Pyrenopeziza brassicae_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=322140>.
- Mod.DHA]
[see also in
the
archive:
2007
---
Foliar diseases, brassica crops - UK 20070913.3037]
