A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases <http://www.isid.org>
In this post:
 Light leaf spot - UK
 Aster yellows - Canada
 Light leaf spot - UK
Date: Fri 19 Oct 2012
Source: Farmers Guardian [edited]
Light leaf spot at record levels in 2012 oilseed rape crop
Latest results from the Defra [Department for Environment, Food and Rural Affairs] winter oilseed rape pest and disease survey show light leaf spot disease levels in oilseed rape crops during pod ripening were among the highest ever recorded.
Light leaf spot on the pods was recorded in 82 percent of crops and on
35 percent of plants. On the stems, the incidence of light leaf spot
-- 97 percent of crops affected and 63 percent of stems -- was the highest recorded since the survey began in 1987.
Light leaf spot was found in all regions of the survey, with the South West having the highest incidence of the disease on pods.
[Additional news stories:
 Aster yellows - Canada
Date: Fri 12 Oct 2012
Source: The Battlefords News Optimist [edited] <http://www.newsoptimist.ca/article/20121012/BATTLEFORD0107/310129996/-1/battleford/aster-yellows-infect-60-of-canola-crops>
Aster yellows infect 60 percent of canola crops
Aster yellows was a problem in the majority of canola fields across the prairies this year , and has been positively identified in cereal crops as well [see ProMED-mail post 20120806.1229839]. We normally have one to 5 percent infection, but 2012 saw up to 60 percent infection in canola.
Aster yellows is transmitted by insects called leafhoppers [and] each plant they feed on becomes infected. With a life span of 100 days or longer, there are a lot of plants that can become infected.
Application of an insecticide registered for leafhoppers may be beneficial if populations are high enough early in the season.
[Byline: Sherrilyn Phelps]
[Light leaf spot
Light leaf spot (LLS) of _Brassica_ species is caused by the fungus _Pyrenopeziza brassicae_. In oilseed rape (_Brassica napus_), 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. In the UK, LLS has caused considerable yield losses of oilseed rape in the past.
Aster yellows phytoplasma (_Candidatus_ Phytoplasma asteris, 16SrI-B taxonomic group) can infect over 300 host species including a wide variety of broadleaf (dicotyledoneous) crops such as oilseed rape, potato ("purple top"), grapevine, lucerne, and some vegetables.
Cereals and other monocots are usually affected to a lesser extent.
Symptoms in oilseed rape (including canola) may include stunting of plants as well as malformation of flowers and pods. Infected plants typically do not produce seed.
Ornamentals and weeds can serve as pathogen reservoirs. The phytoplasma can overwinter in the living crowns of perennials. It can be transmitted by grafting, but not in soil nor by seed. The primary vector appears to be the aster leafhopper (_Macrosteles quadrilineatus_). Acquisition of the pathogen is followed by an incubation period of 2-3 weeks during which the phytoplasma multiplies inside the vector. Insects then remain infectious for life. The pathogen may be present in host species at very low levels; however, the level can increase under favourable conditions resulting in an outbreak with potential crop losses. Disease management in field crops may include vector control and removal of weeds serving as pathogen and/or vector reservoirs. For woody hosts, clean planting and/or grafting material is most important.
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/r/1lNY>
<http://www.lib.utexas.edu/maps/americas/canada_pol_1986.gif> and <http://healthmap.org/r/1ALd>
LLS symptoms on oilseed rape:
<http://www.fwi.co.uk/assets/getasset.aspx?itemid=5232061> (leaf) and <http://www.rothamsted.ac.uk/ppi/pics/llsp_lge.jpg> (pod) Aster yellows symptoms on oilseed rape:
Information on LLS on oilseed rape:
<http://www.rothamsted.ac.uk/ppi/diseases/lls.html>, and <http://apsjournals.apsnet.org/doi/abs/10.1094/PHYTO.2003.93.6.657>
_P. brassicae_ taxonomy:
UK Department for Environment, Food and Rural Affairs (DEFRA):
Aster yellows disease information:
_C._ Phytoplasma asteris taxonomy and strains:
<http://beta.uniprot.org/taxonomy/85620> and <http://ijs.sgmjournals.org/cgi/content/abstract/54/4/1037>
Phytoplasma resource centre, information, and pictures:
<http://www.ba.ars.usda.gov/data/mppl/phytoplasma.html>. - Mod.DHA]
Aster yellows, wheat & barley - Canada 20120806.1229839 Liberibacter, vegetable crops - multicountry 20120713.1199961
Light leaf spot, oilseed rape - UK: increase 20100826.3015 Verticillium wilt, oilseed rape - UK: spread 20100330.1005
Fungal diseases, oilseed rape, maize - UK 20091019.3590 Light leaf spot, oilseed rape - UK 20090226.0795
Fungal diseases, wheat, oilseed rape - UK 20080930.3083 Aster yellows phytoplasma, grapevine - South Africa: update
Light leaf spot, oilseed rape - Ireland, UK 20080403.1225
Aster yellows phytoplasma, canola - Canada: (SK) 20071114.3692 Foliar diseases, brassica crops - UK 20070913.3037
Aster yellows phytoplasma, chili, pigeon pea - India 20060324.0910
Aster yellows phytoplasma, grapevine - Tunisia 20040512.1280 Potato purple top disease - USA (WA, OR) 20040415.1041]