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International Society for Infectious Diseases
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Date: Wed 24 Jul 2024
Source: Michigan State University [summ. Mod.DHA, edited]
https://www.canr.msu.edu/news/michigan-potato-late-blight-detected-on-july-23-2024


Potato late blight has been confirmed in southwestern Michigan, bordering Indiana. The genotype of the _Phytophthora infestans_ pathogen was US-23. The disease was noted in a very small section of a commercial field (about 5 square feet [0.47 sqm]).

Some areas have experienced favourable conditions in the past several weeks due to more frequent and heavy rain events. Preventative foliar programs and diligent crop monitoring are strongly recommended. US-23 can still be managed with phenylamide fungicides.

Since early July [2024], there have been reports of potato and tomato late blight (US-23 genotype) in Ontario, Canada. No other regional detections have been documented.

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Communicated by:
ProMED

[Late blight of potato (PLB) and tomato is caused by the fungus-like organism (oomycete) _Phytophthora infestans_ and can cause 100% crop loss. The pathogen can also affect some other solanaceous crops. In potato, it affects leaves as well as tubers; in tomato, it causes lesions and rotting of leaves, stems and fruits. The disease is favoured by cool, moist conditions. It can spread rapidly within a crop and destroy it within a few days. Under favourable conditions, epidemics in tomatoes may be even more rapid than in potatoes.

The pathogen is spread by plant material (including potato seed tubers, tomato transplants, plant debris, volunteer crop plants), mechanical means (including human and insect activities), wind and water. Disease management requires an integrated approach; it may include removal of pathogen reservoirs, crop rotation, preventative fungicide treatments of planting material, as well as fungicide sprays of crops. Farm saved or uncertified seed tubers have often been reported as sources of PLB outbreaks. Certified clean planting stock and management strategies for fungicide resistance of the pathogen are considered vital to control late blight outbreaks. Commercial crop cultivars vary in susceptibility to late blight. Development of resistant cultivars is being counteracted by the adaptability of the pathogen.

Late blight is considered an increasing problem worldwide. Considerable variation in aggressiveness between different pathogen strains has been observed, but more virulent strains are emerging frequently. The presence of both A1 and A2 mating types of the pathogen increases the chances of strains with additional fungicide resistances and increased yield losses developing.

The A1 strain US-23 in the report above has been predominant in the region in recent years. It is also currently affecting crops in the USA in New York state (see link below). A new A2 strain, US-25, was identified in the region in 2018 (ProMED post 20181025.6110781). Coinfection of both strains would considerably increase the risk of crop losses for growers.

Pictures
Late blight on potato:
https://onvegetables.com/wp-content/uploads/2018/08/Potato-late-blight-No-halo.jpg,
https://www.thompson-morgan.com/static-images/tandm/static-articles/how-to-stop-potato-blight/what-is-potato-blight.jpg and
https://farm1.static.flickr.com/81/281344513_74bbffe5fe.jpg
Late blight on tomato:
https://gardenerspath.com/wp-content/uploads/2021/07/Identify-and-Treat-Late-Blight-on-Tomatoes-FB.jpg,
https://dev.mos.cms.futurecdn.net/4Tae6YFtHhuoRshaDHQ6Ff.jpg and
http://static.agcanada.com/wp-content/uploads/sites/5/2015/09/Late-blight-tomato-stem-leaf.jpg
Microscopy of PLB infected cells:
https://micro.magnet.fsu.edu/optics/olympusmicd/galleries/brightfield/images/potatoblight.jpg

Links
Current PLB outbreak in New York state:
https://hornellsun.com/2024/08/27/cornell-cooperative-update-on-late-blight-outbreak-in-allegany-county/
PLB information with time lapse of PLB symptom development vs. healthy:
https://www.agroscope.admin.ch/agroscope/en/home/topics/plant-production/field-crops/crops/potatoes/diseases/potato-late-blight.html (incl. disease cycle)
Information on late blight:
https://gd.eppo.int/taxon/PHYTIN (with photo gallery),
https://doi.org/10.1079/cabicompendium.40970,
https://cropscience.bayer.co.uk/threats/diseases/potato-diseases/late-blight/,
https://cipotato.org/press_room/blogs/combating-late-blight/ and
https://www.gov.mb.ca/agriculture/crops/plant-diseases/print,mgmt-late-blight-potatoes.html
_P. infestans_ taxonomy & synonyms:
https://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=232148 and
https://www.speciesfungorum.org/GSD/GSDspecies.asp?RecordID=232148
- Mod.DHA

ProMED maps:
Canada: https://promedmail.org/promed-post?place=8718417,12
United States: https://promedmail.org/promed-post?place=8718417,106]

See Also

Late blight, potato - Switzerland 20240530.8716771
Late blight, potato - Jordan: alert 20240306.8715232
2023
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Late blight, potato - India: (PB) 20231219.8713807
Late blight, potato - UK: fungicide resistances Archive Number: 20230126.8707982
2022
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Late blight, potato - Nigeria: (PL) 20220719.8704518
Late blight, potato - Nepal: (KN) 20220203.8701230
2021
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Late blight, potato - Europe, Asia: population changes 20210507.8349166
2020
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Late blight, potato - Russia: (SL) 20200820.7696987
Late blight, potato - Ireland, UK: alert 20200618.7481853
Late blight, potato - India: (PB) 20200113.6887703
Late blight, potato - Africa: strain 33_A2, 1st rep (Nigeria) 20200103.6868372
2019
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Late blight, potato - Europe (02): UK, strain 36_A2 20190712.6562717
Potato diseases - Russia: survey 20190606.6506616
Late blight, potato - Europe: emerging strains 20190416.6424462
Late blight, potato - Nigeria: (PL) 20190130.6286551
2018
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Late blight, tomato - USA: new A2 strain 20181025.6110781
2014
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Late blight, potato & tomato - Canada: strains 20140428.2434165
and additional items on late blight in the archives

Website: http://www.isid.org

Published: August 29, 2024