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Date: Sat 16 May 2009
Source: The Birmingham News [edited]
<http://www.al.com/living/birminghamnews/news.ssf?/base/living/1242461772135500.xml&coll=2>

Tomato blight caused by wet Alabama weather

The cool, wet weather conditions we've been experiencing across Alabama this spring [2009] are very favorable to a fungal disease we don't see every year, but it is a problem this year. The disease is called "late blight." This is a fungus that likes wet conditions that is, frequent rainfall and/or overhead irrigation), overcast skies, and cool temperatures.

The disease can destroy a patch of tomatoes or potatoes in a matter of days. One of the best controls for late blight is an extended period of hot, dry weather. The last time I recall a significant late blight outbreak was back in 1995. That year we had weather patterns similar to what we are currently experiencing. In 1995, we basically had a late blight epidemic in home gardens and in low-acreage farms across the state. The disease was not a significant problem in large commercial fields that year because most commercial growers follow a weekly fungicide spray program.

Control options include avoiding overhead irrigation and a fungicide spray program. This disease spreads very quickly so don't wait too long to start spraying. Try to treat when the product will have a few hours of drying time.

[Byline: Tony Glover]

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[Late blight of tomato and potato is caused by the fungus-like organism _Phytophthora infestans_ and can cause 100 percent crop loss. 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, and in potato it affects leaves as well as tubers. The disease can spread rapidly within a crop and destroy it within a few days. It is spread by contaminated plant and other material, wind and water. Under favourable conditions, epidemics in tomatoes may be even more rapid than in potatoes.

Disease management requires an integrated approach and includes phytosanitary measures, removal of solanaceous weeds and volunteer crop plants serving as pathogen reservoirs, limiting free moisture in the crop, preventative fungicide treatments of planting material (tomato transplants, potato seed tubers), and fungicide sprays of crops. Crop rotation with non-hosts may reduce available inoculum.
While commercial crop cultivars vary in susceptibility to late blight, development of resistant cultivars is being counteracted by the adaptability of the pathogen, with new strains evolving all the time.

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html>  and <http://healthmap.org/r/00cn>
Alabama:
<http://www.alabama-map.org/alabama-road-map.gif>  and <http://www.etsu.edu/math/gardner/sputnik/alabama-map.jpg>

Pictures
Late blight 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>

Links
Late blight 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/>,
<http://www.olympusmicro.com/micd/galleries/brightfield/potatoblight.html>,  and <http://www.agric.wa.gov.au/pls/portal30/docs/FOLDER/IKMP/PW/PH/DIS/VEG/FS0401_REVIEW.PDF>
Late blight information and resources:
<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/> . - Mod.DHA]