A ProMED-mail post
<http://www.promedmail.org>
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International Society for Infectious Diseases <http://www.isid.org>

Date: February 15, 2008
Source: Southwest Florida Online [edited]
<http://swflorida.blogspot.com/2008/02/tomato-blight-appears-in-immokalee.html>

Late blight has been found on tomato and potato plants in several locations around Fort Pierce, and this week Leon Lucas of Glades Crop Care has reported that late blight has been found near Immokalee on tomato plants. This report was confirmed microscopically by the UF/IFAS [University of Florida Institute of Food and Agricultural Sciences] Plant Disease Clinic in Immokalee. At present, barring further reports from Southwest Florida, the find in Immokalee appears to be isolated to one location and limited in area.

Given the fact that late blight is present in South Florida and the weather forecast for the next few days calls for increased chance of showers and conditions conducive to the spread of the disease, growers are advised to increase scouting efforts and apply protectant fungicides, says Gene McAvoy of the Hendry [county] Agricultural Extension Office in LaBelle.

Late blight is caused by the fungus _Phytophthora infestans_, which is a pathogen of potato and tomato. Very few vegetable diseases cause more concern to growers. The disease can spread quickly and devastate a tomato or potato field within a few weeks if not properly controlled said McAvoy. Since the disease can spread so rapidly, McAvoy says growers should scout their fields thoroughly each day, especially when cool and wet conditions conducive to disease development prevail.

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[Late blight caused by the fungus _Phytophthora infestans_ causes a devastating disease of potato and tomato with up to 100 percent crop losses. To a lesser extent, it can also affect other solanaceous crops such as eggplant and capsicum. The pathogen can affect leaves, stems, and fruit of tomato causing spots, lesions, and rotting. The disease can spread rapidly within a crop and destroy it within a few days. It is highly infectious, and once it is found in a region, all susceptible crops nearby are threatened. The disease is favoured by cool, moist conditions, and under favourable conditions epidemics in tomatoes seem to be even more rapid than in potatoes. Spread often occurs on infected tomato transplants or other plant material, by wind, water, or mechanical means. Late blight is not considered a true seed-borne disease. Solanaceous weeds can serve as pathogen reservoirs.

Disease management requires an integrated approach and includes phytosanitary measures, removal of weeds, and volunteer crop plants as pathogen reservoirs, limiting free moisture in the crop, preventative fungicide treatments of planting material, and fungicide sprays of crops. Crop rotation with non-hosts may reduce available inoculum. Commercial tomato cultivars vary in their degree of susceptibility to late blight, but few are resistant. Sources of genetic resistance have been identified in wild relatives of tomato, and breeding programmes are under way.

Late blight is a concern in many countries because new and even more virulent strains are emerging. Two mating types of the fungus exist, and where both are present the chances for fitter strains to evolve are increased further. Since 1990, there have been severe outbreaks of late blight in commercial and garden plantings of potato and tomato in both the US and Canada, which were mostly attributed to new strains, introduced from Mexico.

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html>
and <http://healthmap.org/promed?v=40,-97.6,4>
Florida:
<http://www.mapsofworld.com/usa/states/florida/florida-map.html>
Florida counties:
<http://mapsofworld.com/usa/states/florida/florida-county-map.html>

Pictures
Late blight symptoms on tomato:
<http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2006/23hrt06a3f1.jpg>
Tomato field destroyed by late blight:
<http://www.apsnet.org/online/feature/BioSecurity/Images/lateblightbolkan.jpg>
Late blight on potato:
<http://www.sciencedaily.com/images/2007/01/070102132649.jpg>
 and <http://www-biol.paisley.ac.uk/bioref/Chromista/potato_blight.jpg>
Microscopy of infected cells:
<http://micro.magnet.fsu.edu/optics/olympusmicd/galleries/brightfield/images/potatoblight.jpg> 


Links
Information on late blight of tomato:
<http://www.omafra.gov.on.ca/english/crops/hort/news/hortmatt/2006/23hrt06a3.htm> 

Late blight of tomato and potato, fact sheets:
<http://ohioline.osu.edu/hyg-fact/3000/3102.html>  and <http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_LateBlt.htm>
Disease history and background:
<http://www.apsnet.org/online/feature/lateblit/>,  and <http://www.olympusmicro.com/micd/galleries/brightfield/potatoblight.html>
Late blight information and resources via:
<http://www.potato.org.uk/department/knowledge_transfer/fight_against_blight/advice_blight.html>
_P. infestans_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=232148>
Global Initiative on Late Blight:
<http://gilb.cip.cgiar.org/>
UF/IFAS:
<http://www.ifas.ufl.edu/>.  - Mod.DHA]