Hard Decisions Ahead With Ash Trees By: Stanton Gill, Extension Specialist in IPM and Entomology for Greenhouses and Nurseries Central Maryland Research and Education Center University of Maryland Protect it or cut it down? This decision is one that managers are going to be faced with over the next couple of years where there are green or white ash planted in the landscape. Green and white ash were one of the top selling nursery trees for over 40 years and a lot of them were installed in new communities around office parks throughout the metro area. Many of these trees are now big caliber trees of 15 25 DBH. You heard the saying The bigger they are, the harder they fall. This case will be very true in many landscapes. In May 2013, a meeting was organized to help city managers and arborists understand what we can expect as emerald ash borer continues to establish itself in Maryland. The program organizers brought in urban forester managers from mid-west cities that had to deal with the fall of the ash in the mid-west. They commented that you go through about 3 or 4 years of discovery of the pest in the area followed by a tidal wave of dying trees. This is called the Exponential Death of Trees. You really need to start planning in these early stages because when the Exponential Death of Trees starts, you will have a large number of dead trees that have to be taken down. If you can keep your ash trees alive through the tidal wave, then the population goes down and you are hopefully left with standing trees. The questions are how much are you are willing to spend on protecting the ash trees and for how long? There is no natural resistance to the emerald ash borer among ash trees so the choice is which chemical you apply to the tree to protect its life. You also have to decide when the tree is taken down. Sounds simple, but as many things in life, it is not simple at all. A big tree not only shades areas reducing temperatures in summer, it
absorbs huge amounts of runoff water. Taking down a large tree is going to dramatically change the environment in the area where it was growing. It is also expensive to remove a tree and stump grind out the roots. A replacement tree takes years to grow and fill in an area. Do you inject and save the ash or cut it down? I lean toward removing the tree and starting over with another species of tree but it can be argued it is best to inject and save a tree a little while longer until the tidal wave passes by. The other thing is it may be too expensive to take down all of the ash trees in an area preemptively. Some city foresters are choosing to go out and rate the quality of the ash tree and evaluate its potential hazard if it dies. They rate the trees on a scale of say 1 5 with 5 being the trees that should have priority on being removed. One city in Maryland that has 22,000 ash trees in its tree inventory is choosing to remove 500 ash trees each year, picking the ones with a 5 rating. They are injecting 25-30% of the better ash trees to give them more breathing room before these trees have to be removed. Eventually, the plan is to replace the ash trees with other species of trees and have a mixed species stand of trees to protect against outbreaks of other insects coming in the future. This approach is probably the best long range way of dealing with EAB. The adult beetles will be out in May. Emerald ash borer adults emerge at 450 degree days which is the time when black locust trees are in full bloom. If you are taking action with insecticide treatments, then May and June is the best treatment time for most of the treatments. Adult emerald ash borers range from iridescent green to greenish copper in color
Here is a list of chemicals with time of application and how long they will give control of the emerald ash borer: Table 1. Insecticide options for professionals and homeowners for controlling EAB that have been tested in multiple university trials. Some products may not be labeled for use in all states. Some of the listed products failed to protect ash trees when they were applied at labeled rates. Inclusion of a product in this table does not imply that it is endorsed by the authors or has been consistently effective for EAB control. This table is adapted from the publication Insecticide options for Protecting Ash trees from Emerald Ash Borer by Daniel A. Herms et.al. at: http://emeraldashborer.info/files/multistate_eab_insecticide_fact_sheet.pdf Insecticide Formulation Active Ingredient Application Method Recommended Timing Professional Use Products Merit (75WP, 75WSP, 2F) Imidacloprid Soil injection or drench Xytect TM (2F, 75WSP) Imidacloprid Soil injection or drench Mid-fall and/or mid- to late Mid-fall and/or mid- to late IMA-jet Imidacloprid Trunk injection Early May to mid-june Imicide Imidacloprid Trunk injection Early May to mid-june TREE-äge TM Emamectin benzoate (restricted use) Trunk injection Early May to mid-june Inject-A-Cide B Bidrin Trunk injection Early May to mid-june Safari TM (20 SG) Dinotefuran Systemic bark spray Early May to mid-june Transtect Astro Onyx TM Tempo Sevin SL Dinotefuran Permethrin Bifenthrin Cyfluthrin Carbaryl Soil or Basal Drench Preventive bark and foliage cover sprays TreeAzin Azadirachtin Trunk Bayer Advanced TM Tree & Shrub Insect Control Imidacloprid Homeowner Formulation Soil drench Early May to June 2 applications at 4-week intervals; first spray should occur when black locust is blooming (early May in southern Ohio to early June in mid-michigan) Typical application takes 30-60 minutes per tree. Translocate throughout the tree within 48 hours May to Mid-June Mid-fall or mid- to late
Table 2. This is a table to help you understand how long each of the soil, bark spray or injection treatments will provide control of EAB and approximately what professionals are charging to treat trees per each inch of DBH (diameter at breast height). This is not the actual cost of the chemical, but is the range of what most certified pesticide applicators are charging to make an application to a tree. Imidacloprid Dinotefuran Emamectin benzoate TreeAzin Application method Soil drench or Basal trunk spray or soil injection or drench Trunk Trunk Time of application Fall or May - June May - June May - June May - June Residual control 1 year 5 7 months 2 years 2 years What most applicators charge to treat per 1 inch of DBH $1 - $5 $10- $15 $10 - $15 $20 - $30 In Canada they have severely restricted the chemicals that can be used for insect control. The Canadian Forest Service has backed the development of a 5% Azadirachtin B marketed by BioForest Technology, Inc (Distributed in the US by Rainbow TreeCare) for tree injection that should satisfy the organic type customer. The product is called TreeAzin systemic insecticide. This product is an organic systemic insecticide (OMRI listed) for control of Emerald Ash borers. The Azadirachtin that is extracted from Neem tree seeds acts as an Insect Growth Regulator. The larvae are prevented from completing development and die before they can go to the next instar (growth) stage. When treating with TreeAzin for control of EAB, it is suggested to use between 5 to 18.5 ml per DBH. It has been tested in Canada and is supposedly providing 95% control of EAB larvae. Testing in the United State started in 2013. The product must be stored at 40 70 F and will last one year in storage. When you take it out to the field, it is recommended that you pack the material in a cooler with ice packs to keep it cool. The formulation is very thick and it is injected using large tubes and takes 30-60 minutes to get it into the trees. Back to What to Do In May 2013, the city forester from Fort Wayne, Indiana was asked to come and address arborist and landscape managers on how they dealt with EAB in their city. Chad Tickle, the city forester,
started with the comment As the population of EAB goes up the options go down. His approach is to remove a certain number of ash trees each year and treat a set number of trees to buy time until you have to take the trees down. There just isn t enough money to take all of the ash trees down in most cities on one year s budget. He mentioned that it we are in the early stages in most of Maryland, and you can get lulled into thinking you don t need to do anything. Doing nothing is a bad decision because in 2-3 year you are suddenly faced with many standing, but dead ash trees. During the meeting Nevin Dawson, forestry expert, University of Maryland Extension, commented that the City of Baltimore has over 300,000 ash trees in the city. Baltimore is one city in Maryland that better start developing a plan for dealing with EAB soon. In Fort Wayne, when Chad started in his job in 2008, there were 59,000 street trees in the city limits. In 2013 they have 46,000 trees in the city limits. The reduction in tree numbers is mainly due to the removal of ash trees. They still have ash standing, but not many. Green and white ash trees were 25% of the Fort Wayne city tree plantings in 2008. They started their management program with a tree inventory to know what they have and where the trees are located. They then evaluated the tree health and determined which trees needed to be removed immediately and which trees could be treated with imidacloprid to give them one year of control and at least 2 more years until the tree would be killed by EAB and have to be removed. It is a buying time strategy. Originally in Fort Wayne, they treated 11,000 trees with soil injection of imidacloprid to buy time. Now, they treat 1300 trees per year. Chad also noted that emerald ash borers seem to like green ash the most with white ash being less preferred, but it still will be attacked. Chad told the group that the 14,000 trees in Fort Wayne has cost $7.2 million to take down and treat from 2008 2013. Even with this aggressive plan it is not enough for many people and Chad still receives in over 250 complaints about dead or dying trees in the city from citizens who want immediate action to remove the dead trees in their neighborhood. He said you better be organized and prepared. It is good advice for us here in Maryland. We are not trying to scare anyone with this article, but you need to make sure your clientele understand the choices and the consequences of no action. The University of Maryland, College of Agriculture and Natural Resources programs are open to all and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, or national origin, marital status, genetic information, or political affiliation, or gender identity and expression.