{"id":31540,"date":"2024-08-12T13:39:02","date_gmt":"2024-08-12T17:39:02","guid":{"rendered":"https:\/\/extension.umaine.edu\/publications\/?page_id=31540"},"modified":"2024-08-12T14:36:22","modified_gmt":"2024-08-12T18:36:22","slug":"2417e","status":"publish","type":"page","link":"https:\/\/extension.umaine.edu\/publications\/2417e\/","title":{"rendered":"Bulletin #2417, Protecting Potato Tubers from Late Blight"},"content":{"rendered":"\n

By I. Kutay Ozturk, Extension Potato Pathologist, University of Maine Cooperative Extension<\/em><\/p>\n\n\n\n

For information about UMaine Extension programs and resources, visit extension.umaine.edu<\/a>.<\/strong>
Find more of our publications and books at extension.umaine.edu\/publications\/<\/a>.<\/strong><\/p>\n\n\n\n

This bulletin lists the best management practices for minimizing the risk of spreading late blight to tubers during late-stage growing season, harvest, and storage.<\/p>\n\n\n\n

Vine-killing<\/strong><\/h2>\n\n\n\n

Vine-killing is essential for all potato growers in a late blight season. Late blight requires living host tissue to survive and ensuring that the vines are completely desiccated before harvest is crucial. Green digging, a practice that exposes tubers to pathogens and increases bruises, significantly increases the risk of late blight incidence. Harvesting potatoes is recommended at least two weeks (preferably three weeks) after the vines die down.<\/p>\n\n\n\n

Chemical vine-killing or flaming should be preferred over mechanical vine-killing, as the latter can spread the disease and fail to achieve complete desiccation.  On infected fields, sulfuric acid can be considered for vine-killing.<\/p>\n\n\n\n

Fungicide applications<\/strong><\/h2>\n\n\n\n

It is crucial to continue fungicide applications until the vines are entirely desiccated. Products containing triphenyltin hydroxide, such as Agri Tin and Super Tin, kill spores on contact and can be used during vine-kill to reduce tuber infections dramatically. Late-season mancozeb applications before vine-kill may also limit tuber infections. Various fungicides, including chlorothalonil, fluazinam, cymoxanil, and copper-based products, are available to control late blight. Mefenoxam\/metalaxyl-containing products can be effective on some strains (Table 1). Please refer to the Potato Pest Control Guide<\/a> for the most up-to-date list, and always check product labels before use.<\/p>\n\n\n\n

Table 1.<\/strong> Overview of Phytophthora infestans<\/em> strains, mating types, and mefenoxam sensitivities.<\/p>\n\n\n\n

Strain<\/th>Mating Type<\/th>Mefenoxam\/metalaxyl sensitivity<\/th><\/tr><\/thead>
US-1<\/td>A1<\/td>Sensitive<\/td><\/tr>
US-6<\/td>A1<\/td>Resistant<\/td><\/tr>
US-7<\/td>A2<\/td>Resistant<\/td><\/tr>
US-8<\/td>A2<\/td>Resistant<\/td><\/tr>
US-11<\/td>A1<\/td>Resistant<\/td><\/tr>
US-20<\/td>A2<\/td>Sensitive<\/td><\/tr>
US-21<\/td>A2<\/td>Sensitive<\/td><\/tr>
US-22<\/td>A2<\/td>Sensitive<\/td><\/tr>
US-23<\/td>A1<\/td>Sensitive<\/td><\/tr>
US-24<\/td>A1<\/td>Sensitive<\/td><\/tr>
US-25<\/td>A2<\/td>Resistant<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Harvest and Storage<\/strong><\/h2>\n\n\n\n

Best practices in bruise management are essential to minimize the spread of late blight to tubers since bruises are entry points for pathogens. Vine kill ensures that a good skin set is formed, which reduces bruise risk. Potatoes should be harvested from dry soil when the tuber pulp temperatures are between 45-65 \u00b0F.  <\/p>\n\n\n\n

Treating with phosphite-based fungicides post-harvest can provide additional protection in storage. However, if post-harvest products are used, it is essential to adjust the rate and water volume appropriately following the label recommendations. Too high volumes could cause potatoes to stay wet in storage, creating ideal conditions for other diseases such as bacterial soft rot.  <\/p>\n\n\n\n

Before storage, tubers need to be graded for late blight since late blight can spread from tuber to tuber. After harvest, it is imperative to cool the potatoes to the curing temperature of 50 \u00b0F as quickly as possible. Throughout storage, provide a high ventilation rate and maximize fresh air intake.<\/p>\n\n\n\n

If late blight on tubers is suspected, storing the tubers at 38 \u00b0F with 85% humidity is ideal. \u00a0Processing potato growers are recommended to work with their customers to process late blight suspect potatoes as quickly as possible.<\/p>\n\n\n\n

References<\/strong><\/h2>\n\n\n\n
    \n
  1. Olsen, N., Miller, J. (2015). Checklist for managing late blight approaching harvest and into storage<\/em>. Miller Research. millerresearch.com\/wp-content\/uploads\/2019\/01\/Checklist-for-Managing-Late-Blight-Approaching-Harvest-and-Into-Storage-2015.pdf<\/a><\/li>\n\n\n\n
  2. Saville, A., Graham, K., Gr\u00fcnwald, N. J., Myers, K., Fry, W. E., Ristaino, J. B. (2015). Fungicide sensitivity of US genotypes of Phytophthora infestans<\/em> to six oomycete-targeted compounds. Plant Disease<\/em>, 99<\/em>, 659-666.<\/li>\n\n\n\n
  3. Larson, E. R., Migliano, L. E., Chen, Y., Gevens, A. J. (2021). Mefenoxam sensitivity in US-8 and US-23 Phytophthora infestans<\/em> from Wisconsin. Plant Health Progress<\/em>, 22<\/em>, 272-280.<\/li>\n\n\n\n
  4. Reid, J. (2014). New Strain of Late Blight Discovered. VegEdge, 14(20)<\/em>. Cornell Cooperative Extension. rvpadmin.cce.cornell.edu\/pdf\/veg_edge\/pdf149_pdf.pdf<\/a><\/li>\n\n\n\n
  5. Lacy, M.L., Hammerschmidt, R. (1995). Diseases of Potato: Late Blight<\/em>. Michigan State University Extension. canr.msu.edu\/uploads\/files\/e1802.pdf<\/a><\/li>\n<\/ol>\n\n\n\n

    <\/h3>\n\n\n\n
    \n\n\n\n

    Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.<\/em><\/p>\n\n\n\n

    \u00a9 2024<\/p>\n\n\n\n

    Call 800.287.0274 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu<\/a>.<\/strong><\/p>\n\n\n\n

    The University of Maine System (the System) is an equal opportunity institution committed to fostering a nondiscriminatory environment and complying with all applicable nondiscrimination laws. Consistent with State and Federal law, the System does not discriminate on the basis of race, color, religion, sex, sexual orientation, transgender status, gender, gender identity or expression, ethnicity, national origin, citizenship status, familial status, ancestry, age, disability (physical or mental), genetic information, pregnancy, or veteran or military status in any aspect of its education, programs and activities, and employment. The System provides reasonable accommodations to qualified individuals with disabilities upon request. If you believe you have experienced discrimination or harassment, you are encouraged to contact the System Office of Equal Opportunity and Title IX Services at 5713 Chadbourne Hall, Room 412, Orono, ME 04469-5713, by calling 207.581.1226, or via TTY at 711 (Maine Relay System). For more information about Title IX or to file a complaint, please contact the UMS Title IX Coordinator at www.maine.edu\/title-ix\/<\/a>.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

    By I. Kutay Ozturk, Extension Potato Pathologist, University of Maine Cooperative Extension For information about UMaine Extension programs and resources, visit extension.umaine.edu.Find more of our publications and books at extension.umaine.edu\/publications\/. This bulletin lists the best management practices for minimizing the risk of spreading late blight to tubers during late-stage growing season, harvest, and storage. Vine-killing […]<\/p>\n","protected":false},"author":21,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_kad_blocks_custom_css":"","_kad_blocks_head_custom_js":"","_kad_blocks_body_custom_js":"","_kad_blocks_footer_custom_js":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"class_list":["post-31540","page","type-page","status-publish","hentry"],"yoast_head":"\nBulletin #2417, Protecting Potato Tubers from Late Blight - Cooperative Extension Publications - University of Maine Cooperative Extension<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/extension.umaine.edu\/publications\/2417e\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Bulletin #2417, Protecting Potato Tubers from Late Blight - Cooperative Extension Publications - University of Maine Cooperative Extension\" \/>\n<meta property=\"og:description\" content=\"By I. 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