Emerald Ash Borer Detections and Treatment Horizon

Abe Nielsen, Kentucky Division of Forestry Forest Health Specialist, reported first detections of emerald ash borer infested trees at locations in Clinton, Cumberland, and Wayne counties. The map (Figure 1) shows the extent of the known infestation.

Figure 1. The emerald ash borer has been found in counties marked in green.

Is Preventive Treatment Worth It?

(From Insecticide Options for Protecting Ash Trees from Emerald Ash Borer, 2014 link)

The economics of treating ash trees with insecticides for emerald ash borer (EAB) protection are complicated and depend on several factors. Consider tree size, health, location, value, as well as treatment cost, the likelihood of success, and potential costs of removing the trees. Scientists have compared costs of removing urban ash trees versus treating the same trees with emamectin benzoate, which provides 2 years of EAB control. Results consistently show treatment costs are much lower than removal costs. As treatment options continue to evolve, costs of treatment will likely change. It will be important to stay up-to-date on these options and management recommendations.

Benefits of treating trees can be more difficult to quantify than costs. Healthy landscape trees typically increase property values, provide shade and cooling, and contribute to the quality of life in a neighborhood. In addition, landscape trees, especially mature trees, capture storm water, reducing potential pollution of streams and rivers. The economic benefits provided by trees increase with the size of the tree, as does the cost of removal. Many people are sentimental about their trees. These intangible qualities are important and should be part of any decision to invest in an EAB management program. Hence, it may be particularly economical to treat larger trees.

Figure 2. Treated versus non-treated ash trees in Napierville, IL (http://www.isa-arbor.com/ )

The size of EAB populations in a specific area will change over time. Populations initially build slowly but increase rapidly as more trees become infested. As EAB populations reach peak densities, a high proportion of the untreated ash trees in a given area will decline and die, usually over a 3- to 5-year period. Once untreated ash trees in the area succumb, however, the local EAB population will decrease substantially. Ongoing studies in southeast Michigan and northwest Ohio, for example, indicate EAB populations still persist but at much lower densities simply because few mature ash trees remain in this area. Young ash saplings in forests or woodlots will likely be colonized by EAB eventually, so landscape ash may continue to face some risk of EAB infestation. It seems likely, however, that surviving ash trees can be managed with less frequent treatments once the EAB invasion has passed. Studies on the dynamics of EAB populations and whether the intensity of insecticide treatments can decrease after the local EAB population has collapsed are underway in Michigan and Ohio.

 

By Lee Townsend, Extension Entomologist

 

Posted in Forest Trees, Landscape Trees & Shrubs