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Date: 13 Jan 2009
Source: Farmers Weekly [edited]
<http://www.fwi.co.uk/Articles/2009/01/13/113769/high-potato-black-dot-infections-serve-as-warning-for.html>

High potato black dot infections serve as warning for 2009

High black dot levels in potatoes in the past 2 years should serve as a warning to growers to check this year's [2009] field history for the disease, and consider having soil inoculum levels tested, advisers suggest.

Levels of the fungal blemish have been higher this year, says Paul Coleman of Greenvale AP [potato producers]. Heavy rain before and after desiccation [of plants] helped push infectious spores down to the tubers, he explains.
"It also meant harvest in quite a lot of cases was delayed from 3 weeks to
4 or 5 weeks after desiccation. Black dot seems to be getting worse."

That extra period in the ground is critical for the development of the disease, Jeff Peters from the Central Science Laboratory [UK Ministry of Agriculture Fisheries and Food] notes. "The amount of black dot that develops is proportionate to the time the crop is in the ground from emergence to harvest." Research suggests growers who know they have a high risk from either having their soil tested or from previous field history, should look to minimise the number of days crops are in the ground, Dr Peters says.

[byline: Mike Abram]

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[Black dot of potato is caused by the fungus _Colletotrichum coccodes_. The pathogen can also affect tomato, soybean, oilseed rape, oats, lucerne, and a number of solanaceous weeds which may serve as pathogen reservoirs. On potato, symptoms include black dots (sclerotia) and lesions on roots, stems, leaves, and tubers. Severe infection can cause large brown patches, tuber shrivelling, and may lead to wilting and root rot. Lesions may deepen when tubers are stored after harvest. Up to 30 per cent yield loss due to the early death of infected plants has been reported.

The pathogen is soilborne and may be spread by infected plant debris, tubers, soil, and mechanical means. Disease management is difficult because there are few effective fungicides and little varietal resistance in current potato cultivars. Cultural procedures such as crop rotation and minimising inoculum are used to achieve some control of the pathogen.

Maps of UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif>  and
<http://healthmap.org/promed?v=54.5,-2,5>
Pictures
Black dot symptoms:
<http://www.panhandle.unl.edu/potato/assets/images/autogen/a_Black_Dot_on_tuber_skin.jpg>
(tuber),
<http://ipmnet.org/plant-disease/plant_images/Potato_Black_Dot.jpg>  (leaves),
<http://ipmnet.org/plant-disease/plant_images/Potato_Black_Dot_stem.jpg> (stems) and
<http://ipmnet.org/plant-disease/plant_images/ACFJGA0nA_Wo.jpg> (close-up of tuber lesion)
Affected potato field with early dying plants:
<http://www.ars.usda.gov/images/docs/15116_15310/russet%20diseased.jpg>
Black dot photo gallery:
<http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Potatoes/BlackDot/PotBlkDtPhotoList.htm>
Links
Black dot disease information and fact sheets:
<http://www.potato.org.uk/department/sbeu/potato_diseases/index.html?did=48&pg=1>, 

<http://ipmnet.org/plant-disease/disease.cfm?RecordID=883>,
<http://www.panhandle.unl.edu/potato/html/black_dot.htm>,
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_BlkDot.htm>,
<http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Potatoes/BlackDot/PotBlkDotFS6.htm>
and
<http://www.ars.usda.gov/Research/docs.htm?docid=15116&page=2>
_C. coccodes_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=295323>
Greenvale AP:
<http://www.greenvale.co.uk/>
UK Central Science Laboratory:
<http://www.csl.gov.uk/> - Mod.DHA]

[see also in the archive:
2003
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Black dot disease, potato, atypical lesions - France 20031111.2795]