{"id":118,"date":"2019-06-14T08:51:35","date_gmt":"2019-06-14T12:51:35","guid":{"rendered":"http:\/\/site.extension.uga.edu\/vidaliaonion\/?p=118"},"modified":"2019-06-14T08:51:35","modified_gmt":"2019-06-14T12:51:35","slug":"black-mold-in-vidalia-onions-quick-facts","status":"publish","type":"post","link":"https:\/\/site.extension.uga.edu\/vidaliaonion\/2019\/06\/black-mold-in-vidalia-onions-quick-facts\/","title":{"rendered":"Black Mold in Vidalia Onions: Quick Facts"},"content":{"rendered":"<figure id=\"attachment_122\" aria-describedby=\"caption-attachment-122\" style=\"width: 777px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-122\" src=\"https:\/\/site.extension.uga.edu\/vidaliaonion\/files\/2019\/06\/black-mold.jpg\" alt=\"\" width=\"777\" height=\"495\" srcset=\"https:\/\/site.extension.uga.edu\/vidaliaonion\/files\/2019\/06\/black-mold.jpg 777w, https:\/\/site.extension.uga.edu\/vidaliaonion\/files\/2019\/06\/black-mold-300x191.jpg 300w, https:\/\/site.extension.uga.edu\/vidaliaonion\/files\/2019\/06\/black-mold-768x489.jpg 768w, https:\/\/site.extension.uga.edu\/vidaliaonion\/files\/2019\/06\/black-mold-217x138.jpg 217w\" sizes=\"auto, (max-width: 777px) 100vw, 777px\" \/><figcaption id=\"caption-attachment-122\" class=\"wp-caption-text\">Photo Credit: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org<br \/>Creative Commons License licensed under a Creative Commons Attribution-Noncommercial 3.0 License.<br \/>https:\/\/www.invasive.org\/browse\/detail.cfm?imgnum=1571411<\/figcaption><\/figure>\n<h3><strong><u>Quick Facts About Black Mold in Onions<\/u><\/strong><\/h3>\n<p>There have been some questions about Black Mold in onions the last couple of weeks.\u00a0 I wanted to share with you what we know about the disease, and some possible considerations on management.<\/p>\n<p>For many of you, this may be old news, but I wanted to share some basic facts about the disease as a refresher for myself and those who aren\u2019t familiar with it.<\/p>\n<p><strong><u>Background\/History:<\/u><\/strong>\u00a0 Black mold of onions is a fungal disease.\u00a0 The scientific name of this pathogen is\u00a0 \u00a0<em>Aspergillus niger. <\/em>It is found around the world, and it can affect many other crops.\u00a0 The spores that cause the disease are everywhere, in the soil and in the air. It usually only poses an issue with onions when conditions are right for it to develop (hot and humid).<\/p>\n<p><strong><u>Symptoms:<\/u><\/strong>\u00a0 The fungus is first detected as an area covered with a black sooty mass (made up of microscopic spores) on the neck or outer scales, where injury, disease, or toppling of the foliage has caused an opening in the skin. Fungal spores may develop between dry, dead outer scales and the first inner fleshy scales of the bulb.<\/p>\n<p><strong><u>Disease cycle:<\/u><\/strong> The Black Mold fungus grows on dead plant and animal tissues and spores are very common in the air and soil everywhere.\u00a0 Infection of onion bulbs can occur in the field or in the packing shed.\u00a0 Infection frequently occurs through injured tissue, such as from cuts, bruises, or damage from other onion diseases.\u00a0 Temperature and humidity play a crucial role in the development of the disease:<\/p>\n<ul>\n<li>The <strong><u>minimum<\/u><\/strong> temperature for growth of Black Mold is <strong><u>59<sup>0<\/sup>F<\/u><\/strong>.<\/li>\n<li>The <strong><u>optimum<\/u><\/strong> temperature for growth of Black Mold is <strong><u>82<sup>0<\/sup> \u2013 93<sup>0<\/sup>F<\/u><\/strong>.<\/li>\n<li>Black Mold will <strong><u>not grow<\/u><\/strong> in temperatures <strong><u>greater than 116<sup>0<\/sup>F<\/u><\/strong><\/li>\n<li>Fungal growth is significantly <strong><u>slowed<\/u><\/strong> when the relative humidity is <strong><u>below 76%<\/u><\/strong><\/li>\n<li>When the relative humidity is <strong><u>above 81%<\/u><\/strong>, growth can occur <strong><u>rapidly<\/u><\/strong> (3-6 hours).<\/li>\n<li>Free moisture must be present on onions for 6 \u2013 12 hours for infection to occur. This can easily happen in the field, and also in the packing shed when onions \u201csweat\u201d from cooling or temperature changes.<\/li>\n<\/ul>\n<p><strong><u>Past Research and Findings from UGA:<\/u><\/strong><\/p>\n<ul>\n<li>Three on-farm trials were conducted in Toombs and Tattnall 2013 and 2014 to see if fungicides could be used in the field to reduce black mold, and to look at how on farm drying of onions affects the disease. None of the products used significantly reduced the disease.\u00a0 Drying onions also increased the severity and incidence of Black Mold. Read the full report here: <a href=\"https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20114_1.PDF\">https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20114_1.PDF<\/a><\/li>\n<\/ul>\n<ul>\n<li>In 2012, UGA conducted a trial looking at post-harvest fungicides to control black mold in Vidalia Onions.\u00a0 These products helped control the disease, but logistics\/feasibility\/cost could prohibit this practice.\u00a0 See the full report here: <a href=\"https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20109_1.PDF\">https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20109_1.PDF<\/a><\/li>\n<li>There have also been some questions about different storage types (CA, refrigeration, ozone) and if one is better than the other for black mold.\u00a0 Some evidence would suggest that ozone may help, but I have not been able to find any UGA research to support this.\u00a0 If you know of any research from somewhere else that has been done with storage facilities and black mold, please let me know.\u00a0 This may be something we need to look at in the future.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p><strong><u>Management:<\/u><\/strong><\/p>\n<ul>\n<li>In the field, manage your onions for other diseases. These can weaken the plant and create an entry point on onions for Black Mold.<\/li>\n<li>Timeliness! Prompt harvest and post-harvest management of onions is critical, especially as temperatures rise later in the season.<\/li>\n<li>Minimize bruising or injury of tissue. This includes during harvesting, transport, pre-grading, grading, and packing. Bruises or injury that are not obvious to the naked eye create entry points for the disease.<\/li>\n<li>Minimize \u201csweating\u201d of onions during cooling\/drying process. This creates moisture needed for Black Mold to develop.<\/li>\n<li>Temperature and Humidity control are critical: Below 60<sup>0<\/sup>F and under 76% relative humidity is best.<\/li>\n<li>Heated drying of Vidalia Onions is necessary in most situations. Keep in mind, however, that this process often makes Black Mold worse (because we dry at temperatures optimal for development of the disease), especially if the onions already have an established infection.<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<p>Sources for this info:<\/p>\n<p>Schwartz, Howard F., Mohan, S. Krishna, et al. \u00a0\u201cCompendium of Onion and Garlic Diseases.\u201d\u00a0 APS Press, 1995.<\/p>\n<p>Sanders, F.H. Jr, Langston, D.B., Foster, M. \u201cBlack Mold Post Harvest Fungicide Trial, 2012.\u201d Georgia Onion Research-Extension Report. <a href=\"https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20109_1.PDF\">https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20109_1.PDF<\/a><\/p>\n<p>Sanders, F.H. Jr, Riner, C.M., Edenfield, J., Tyson, C.T., and Foster, M. \u201cEffect of Pre-harvest Fungicide Sprays and Commercial Drying on Black Mold of Onion.\u201d\u00a0 <a href=\"https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20114_1.PDF\">https:\/\/secure.caes.uga.edu\/extension\/publications\/files\/pdf\/AP%20114_1.PDF<\/a><\/p>\n<p>UC IPM Pest Management Guidelines: Onion and Garlic, UC ANR Publication 3453. <a href=\"https:\/\/www2.ipm.ucanr.edu\/agriculture\/onion-and-garlic\/black-mold\/\">https:\/\/www2.ipm.ucanr.edu\/agriculture\/onion-and-garlic\/black-mold\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Quick Facts About Black Mold in Onions There have been some questions about Black Mold in onions the last couple of weeks.\u00a0 I wanted to share with you what we know about the disease, and some possible considerations on management. For many of you, this may be old news, but I wanted to share some [&hellip;]<\/p>\n","protected":false},"author":97,"featured_media":122,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"class_list":["post-118","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-vidalia-onion"],"_links":{"self":[{"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/posts\/118","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/users\/97"}],"replies":[{"embeddable":true,"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/comments?post=118"}],"version-history":[{"count":6,"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/posts\/118\/revisions"}],"predecessor-version":[{"id":125,"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/posts\/118\/revisions\/125"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/media\/122"}],"wp:attachment":[{"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/media?parent=118"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/categories?post=118"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/site.extension.uga.edu\/vidaliaonion\/wp-json\/wp\/v2\/tags?post=118"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}