Protect Your Clients’ Ash Trees

Source: www.TurfMagazine.com

Ash trees are popular and attractive street trees and very common in municipal parks, on college grounds, and on residential and commercial landscapes. They’re valued for their shade-producing canopy, medium height, sturdy trunks and, in several popular species, attractive fall color. All of this is being lost.

PHOTO BY JARED SPOLOWSKY, N.Y. STATE DEPT. OF AGRICULTURE AND MARKETS.

In a scenario reminiscent of the Dutch elm disease that wiped out native, nonresistant elms in much of North America by the mid to late 20th century, another unwanted invasive species from Asia is creating similar havoc on ash trees. While the elms fell victim to a destructive fungus that was spread from tree to tree by bark beetles, the culprit this time is the insect itself, the emerald ash borer (EAB).

The EAB, discovered near Detroit in 2002, is devastating ash trees throughout the eastern United States and Canada. It is believed to have entered the country on pallets or some other wood products delivered via ship through the St. Lawrence Seaway and the Great Lakes.

The EAB is now found in more than 14 states and two Canadian provinces. In the 25-state area emanating from Detroit, as many as 38 million landscape ash trees are at risk. Responses include treatment, removal and replacement of more than 17 million ash trees at an estimated cost of $10.7 billion, says the U.S. Forest Service.

While the optimum time to treat ash trees is months away, landscapers and grounds care pros should start researching treatment and pricing options now so they’re ready when customers or, in the case of grounds departments, their employers seek their help.

Presently there are three main treatment options: trunk injection, soil application and bark sprays. And, depending on the preferred application method, one of three different primary active ingredients are used. Emamectin benzoate (the active ingredient contained in TREE-äge insecticide) is used for trunk injection. Imidacloprid is used in most soil drench methodologies and many trunk injections. Dinotefuran is used in bark sprays.

Trunk Injection – Emamectin benzoate (brand name Tree-äge) provides two years of control for EAB with a single trunk injection application, claims its supplier Arborjet. This method uses a plug that seals a precise dose inside the tree without exposing chemicals to the soil, water or air at the time of injection.

Several other trunk injection methods are employed using the same active ingredient commonly used in soil drench applications, imidacloprid. Most require an annual treatment.

Soil Application – Soil drench or soil injection applications must be reapplied every year to maintain protection. For municipalities or treatments on large lots, soil applications are limited by the amount of product you can apply per acre. This may limit you to as few as four to eight trees per acre. This is not a great option for cities, that may have dozens of ash trees per acre. These products must be applied well in advance of an expected outbreak or attack, as it may take 10 to 14 weeks for these types of products to reach the pests after applied to the soil.

Bark Sprays – Bark sprays have had limited use, shorter residuals, must be applied closer to infestation occurrences, and have been shown to be less effective on larger trees. These tend to cost more than soil drenches and must still be applied annually to protect the tree. While bark sprays are faster-acting than soil drenches, they are not as long-lasting, so timing of application is even more critical.

This photo shows how bad EAB damage can be on a tree.
PHOTO BY EDWARD CZERWINSKI, ONTARIO MINISTRY OF NATURAL RESOURCES.

Treatment effectiveness depends on the active ingredient used and the method chosen to apply that chemistry. Any treatment made to the soil with currently labeled products will provide approximately a single year of protection. Bark sprays will also provide just one season of protection. Most trunk-injected products also provide a single year of protection. Some have limits to the number of trees per acre per year, while all seem to be less effective under heavy EAB attack and/ or when tree size is larger. Emamectin benzoate trunk injection provides two years of control.

While each state has its own regulations requiring licensure, certified pesticide applicators (or applicators under their direct supervision) are allowed to make these treatments. Lawn service contractors can offer EAB treatments to residential and commercial customers. Many cities and universities will have grounds crews perform injections; however, others will put injections out to a formal bid for which contractors may be eligible.

Regardless of the chemical product, applicators must strictly follow its label directions. Beyond that, product suppliers also often provide training materials, such as DVD videos and hands-on events.

Contractors that offer (or are considering offering) EAB treatments should also ask product suppliers about the availability of door hangers, flyers and brochures. These have a dual-purpose; they help educate customers, and they’re great marketing tools.

Cost and pricing

Obviously, cost is a big factor when property managers or homeowners consider whether to protect their ash trees or not.

One of the greatest misunderstandings for injection is cost and how to price. In fact, for most cities that have chosen to treat for EAB, the most powerful argument has been how much money they can actually save by treating their city trees instead of removing them.

In general, for an average size healthy tree, most applications will take 10 to 15 minutes or less. Healthier trees will move these products through their vascular systems more rapidly than those already compromised by EAB. Preventative treatment is always the preferred method. Trees under extreme stress, like drought-stressed or damaged ones, will also have slower uptake. During summer months, treatment speed can be hastened by asking customers to water the day before and by treating early and later in the day.

Pricing is generally calculated based on the diameter of the tree. Diameter is measured at 4.5 feet above the ground, or diameter at breast height (DBH). The DBH will determine the volume of product to be injected. Experience has shown that on municipal jobs with large numbers of trees, the price may be as low as $6 per DBH, sometimes lower, while for most residential properties the average is between $8 and $12 per inch, with ranges between $7 and $15 per inch. Applicators have been known to produce as much as $3,000 per day.

Treatment a better option

Whether municipal or residential, the cost of removal and replacement is so high (municipal costs range from $750 to $1,000 per tree) that a tree can be treated for 20 to 40 years before the cost of treating equals the cost of removing and replacing, and they get to keep their tree.

For trunk injection, the guideline is that applications can begin once leaves have matured on the tree. This typically means early May in the southern regions of EAB infestations to late May in more northern regions. Treatment can continue with temperatures below 90 degrees and with adequate soil moisture through the summer and cease when leaves are changing color, as transpiration slows dramatically. In the North, this is typically around the first week of October, but may be extended further south.

The peak of EAB larval damage occurs between August and October. This is important because you need to consider the time required for uptake and protection, the products’ properties, and the EAB life cycle. Because most soil drench products using imidacloprid require 10 to 14 weeks to translocate from the soil to the trunk at a sufficient dose, these applications must be made early enough in the year to protect during larval peak activity. Thus, the recommendation for most soil drench products is early spring applications. Applications of dinotefuran (most bark sprays) are made closer to the point when EAB larvae are expected because they have shorter residuals, so they are often applied in late spring.

The tree on the left was not treated for EAB like the one on the right. Notice the difference between the two.
PHOTO COURTESY OF ARBORSYSTEMS.

Customer communication

Whether or not a contractor provides a written warranty, every time a professional steps on a property, a performance warranty is assumed. A professional can feel confident telling the customer that their treatment, based on research and field use, will offer them a good chance of saving their tree from EAB.

Be careful making similar assurances in regards to treating trees clearly showing canopy thinning, woodpecker feeding or epicormic sprouting (new branches in the center of the tree), as these are clearly signs that EAB is attacking the tree. Research has shown that once a tree reaches over 40 to 50 percent canopy thinning, the chances of recovery diminish greatly due to cambial damage. We have seen trees recover with this much damage, but most cities set limits on a maximum of 25 percent canopy thinning in their decision to treat. The most effective treatment is always a preventative one.

Always read and follow label instructions before buying or using these products. The instructions contain important conditions of sale, including limitations of warranty and remedy. Some products, such as TREE-äge insecticide, carry a restricted use pesticide designation and may only be sold to and used by a state-certified applicator or by persons under their direct supervision. Some products are not registered for use in all states. Please check with your state or local extension service prior to buying or using this product.

The author has 30 years of experience in the green industry, from managing retail stores to his current role as director of urban forestry at Arborjet.