{"id":33130,"date":"2025-05-23T08:48:10","date_gmt":"2025-05-23T12:48:10","guid":{"rendered":"https:\/\/www.purdue.edu\/fnr\/extension\/?p=33130"},"modified":"2026-04-24T15:52:41","modified_gmt":"2026-04-24T19:52:41","slug":"revisiting-ash-tree-protection-purdue-landscape-report","status":"publish","type":"post","link":"https:\/\/www.purdue.edu\/fnr\/extension\/revisiting-ash-tree-protection-purdue-landscape-report\/","title":{"rendered":"Revisiting Ash Tree Protection, Purdue Landscape Report"},"content":{"rendered":"

Purdue Landscape Report<\/em><\/a>: Recently, there has been an uptick in questions related to one of Indiana\u2019s most notorious invasive pests: the emerald ash borer.\u00a0 Homeowners, businesses, even professionals have asked if ash trees are still present in Indiana, and if the insect is still a threat to our ecosystem.\u00a0 Emerald ash borer wreaked significant havoc among Indiana\u2019s hardwoods, and a person could be forgiven for believing that there are no ash trees at all in our state, but this is simply not true.\u00a0 Ash still survives in Indiana and can be found both as ornamental plantings and in untended woodlots; unfortunately, emerald ash borer is also still present and just as deadly to them as ever.\u00a0 The question of protecting ash versus removal them is complex, but entomologists and tree specialists have learned from this insect\u2019s invasion.<\/p>\n

\"Figure<\/a>

Figure 1. Side view of EAB, John Obermeyer<\/p><\/div>\n

The emerald ash borer (Agrilus planipennis<\/em>), a wood-boring insect native to Asia, is responsible for decimating ash (Fraxinus\u00a0<\/em>spp.) throughout the United States and elsewhere.\u00a0 In Indiana, this insect\u2019s presence was confirmed in 2004, though it had probably been in the state for some time before then.\u00a0 Since its arrival, Hoosiers have been forced to watch as ash trees have rapidly declined and died due to the insect\u2019s feeding and life cycle.\u00a0 The insect lays its eggs in crevices in the bark of an ash that is 8 to 10 years old, and after hatching, the new larvae begin to bore through the tree\u2019s cambium tissue. The tree relies on its cambium tissue to transport water and nutrients and supply cells for new growth.\u00a0 Often, the only signs of the insect\u2019s presence are a reduction in canopy coverage and D-shaped exit holes in the bark, indicating adult emergence. \u00a0As time goes on, however, the tree will continue to lose canopy, experience limb death, and often have large chunks of bark detach. Unprotected trees will typically die within 2 to 5 years of infestation.\u00a0 Dead and dying ash trees represent a serious hazard to health and property as infestation will leave them extremely brittle. Brittle ash will often fall during weather events or even collapse over time as limbs fall off.<\/p>\n

While emerald ash borer did significant damage to ash tree populations in Indiana, they did not destroy the population entirely.\u00a0 While virtually all untreated trees will eventually become infested, saplings with a trunk diameter of \u00bd to 1 inch will remain untouched, allowing annual replacement of trees to continue.\u00a0 Since the initial invasion killed so many trees, the borer\u2019s populations have been proportionally reduced as well due to a lack of a food source.\u00a0 This combination of factors has created a cycle of growth and infestation that allows both populations to survive, but at significantly lower levels as compared to the period of the initial infestation.\u00a0 Unfortunately, this also means that emerald ash borer is now a permanent fixture in the hardwood ecosystem in Indiana.<\/p>\n

\"Figure<\/a>

Figure 2. This photo illustration shows three ash trees in Bloomington, Indiana, with different levels of canopy lost to the emerald ash borer. (Purdue Tree Doctor app illustration\/Cliff Sadof)<\/p><\/div>\n

While many may believe ash trees are a total loss, there are still options to protect ash tree and even rescue ash that have already been infested.\u00a0 The first step in this process is to determine the extent of damage in a given tree.\u00a0 As the cambium tissue is consume by ash borer larvae, the tree will experience a steady loss of canopy and limb death.\u00a0 The proportion of lost canopy makes a great indicator for treatment viability.\u00a0 For example, a tree that has only lost 10% of its canopy will normally respond well to treatment.\u00a0 As more canopy is lost, recovery is more challenging, until the tree has lost %30 of canopy coverage.\u00a0 After that point, there is very little chance that a rescue treatment will be successful, and removal will most likely be necessary.\u00a0 It is also important to remember that limb death may occur; these limbs will not recover and will need to be removed to avoid any potential hazards.<\/p>\n

There are several insecticides with varying ranges of efficacy that can be used to manage emerald ash borer.\u00a0 These include imidacloprid, dinotefuran, azadirachtin, and emamectin benzoate. Several studies have been conducted to find the best combination of chemical and application type, such as the difference between using a soil drench compared to a trunk injection. While all of the above chemicals can be effective against the insect, the combination of emamectin benzoate applied through a trunk injection offers the best, longest lasting protection from infestation.\u00a0 This combination has a durable effect lasting for two years under dense infestations.\u00a0 However, the reduction in emerald ash borer populations have spread the distribution of the insect thinner, and longer intervals between treatments are possible.\u00a0 A ten-year study conducted by Purdue University demonstrated that treating trees once every three years provided sufficient protection from the beetles, while also showing that 4 to 5 years after last treatment coincided with an increase in damage to the trees.\u00a0 This same study also found that by six years post-treatment, the trees would decline to the point of making removal a necessity.\u00a0 This research concluded that increasing time between intervals after three years increased the risk of catastrophic damage due to emerald ash borer activity, thus the recommendation for three-year intervals.<\/p>\n

Ultimately, many will see this as a financial issue: the cost of treatment over time against the cost of removal to avoid potential damages.\u00a0 The above study estimated the cost of treating a single tree with an emamectin benzoate injection at $300 per treatment. Since treatment only needs to happen once every three years, the cost per year per tree would be $100, approximately.\u00a0 Tree removal was estimated between $1800 and $3600, depending on tree location and other factors.\u00a0 Also consider replacement costs if you wanted to continue to grow ash in that area, and how long the tree would need to grow to match the size of the tree you just replaced.\u00a0 Additionally, add in any treatment costs to make sure it survives infestation.\u00a0 When looked at from this angle, maintaining regular treatment on rescuable trees would appear to be the most cost-effective route for managing ash.\u00a0 Any treatment plan should be discussed with a professional, such as a certified arborist.<\/p>\n

Read the original article posted in the Purdue Landscape Report April 2025 Newsletter: Revisiting Ash Tree Protection<\/a>.<\/p>\n

Subscribe and receive the newsletter: Purdue Landscape Report Newsletter<\/a>.<\/p>\n

Resources:
\n<\/strong>New Hope for Fighting Ash Borer<\/a>, Got Nature? Purdue Extension-FNR
\nInvasive Pest Species: Tools for Staging and Managing EAB in the Urban Forest<\/a>, Got Nature?
\nEmerald Ash Borer<\/a>, Purdue Extension-Entomology
\nEmerald Ash Borer Tools & Resources<\/a>\u00a0\u2013 Purdue Extension Entomology
\nPlanting Your Tree Part 1: Choosing Your Tree<\/a>, Purdue Extension YouTube Channel
\nTree Planting Part 2: Planting a Tree<\/a>, Purdue Extension – Forestry and Natural Resources YouTube Channel
\nIndiana Invasive Plant List,<\/a> Indiana Invasive Species Council, Purdue Entomology
\nLandscape Report Shares Importance of Soil Testing,<\/a> Purdue FNR Extension
\nFind an Arborist<\/a> website, Trees are Good, International Society of Arboriculture (ISA)
\nTree Risk Management<\/a> \u2013 Got Nature? Blog, Purdue Extension \u2013 FNR
\nID That Tree<\/a> – Video Playlist, Purdue Extension \u2013 Forestry and Natural Resources (FNR) YouTube Channel
\nPurdue Arboretum Explorer<\/a>
\nConservation Tree Planting: Steps to Success<\/a>, Purdue Extension \u2013 FNR YouTube Channel
\nA Woodland Management Moment<\/a>, Playlist, Purdue Extension \u2013 FNR YouTube Channel
\nWoodland Stewardship for Landowners<\/a>, Playlist, Purdue Extension \u2013 FNR YouTube Channel
\nIndiana Department of Natural Resources: Invasive Species<\/a>
\nIndiana Invasive Species Council<\/a>
\nCooperative Invasive Species Management Area (CISMA)<\/a>
\nReport Invasive<\/a>, Purdue Extension
\nNative Trees of the Midwest<\/a>, Purdue University Press
\nProfessional Forester<\/a>, Indiana Forestry Woodland Owners Association
\nForest Improvement Handbook<\/a>, The Education Store<\/p>\n

Bob Bruner<\/a>, Exotic Forest Pest Educator
\nPurdue Entomology<\/p>\n

<\/div>\n","protected":false},"excerpt":{"rendered":"

Purdue Landscape Report: Recently, there has been an uptick in questions related to one of Indiana\u2019s most notorious invasive pests: the emerald ash borer.\u00a0 Homeowners, businesses, even professionals have asked if ash trees are still present in Indiana, and if the insect is still a threat to our ecosystem.\u00a0 Emerald ash borer wreaked significant havoc […]<\/p>\n","protected":false},"author":62,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[80,47,54,622],"tags":[331,330,60,261,65,895,408,72,1113],"class_list":["post-33130","post","type-post","status-publish","format-standard","hentry","category-trees","category-invasiveinsects","category-wildlife","category-woodlands","tag-ash-tree","tag-emerald-ash-borer","tag-forestry","tag-indiana","tag-invasive-insects","tag-purdue-landscape-report","tag-trees","tag-wildlife","tag-woodland","audience-for-enthusiasts","audience-for-homeowners","audience-for-landowners","audience-for-professionals"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts\/33130","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/users\/62"}],"replies":[{"embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/comments?post=33130"}],"version-history":[{"count":10,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts\/33130\/revisions"}],"predecessor-version":[{"id":41110,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/posts\/33130\/revisions\/41110"}],"wp:attachment":[{"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/media?parent=33130"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/categories?post=33130"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.purdue.edu\/fnr\/extension\/wp-json\/wp\/v2\/tags?post=33130"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}