For the past seventeen years, the neighborhood has rallied behind SOE's efforts to protect our heritage trees from Dutch elm disease (DED). Volunteers have applied over 50,000 microinjectors at a cost of over $200,000. We're confident these efforts have slowed the spread of DED, but the tree loss rate in the past three years has been cause for concern and is prompting new action.
The SOE Board has evaluated new ways to protect the Ladd's Addition grove from DED. The Board consulted with other urban foresters and scientists from the US Department of Agriculture to understand the latest best practices in management of urban elm groves. The results of that research indicate that microinjection, the process SOE has used in recent years to protect our elms, is not effective at distributing fungicides to the crown of trees where the elm bark beetle often infects new growth. Further, the fungicides available for microinjection have not been shown to persist and protect trees for more than two years. Thus, our three year cycle of microinjection is not providing adequate protection. Because of the root flare damage (i.e., drilling) done during injections, we cannot inoculate the trees every year.
The preferred alternative to microinjection is a process called macroinfusion, in which Arbortect fungicide is heavily diluted with water and pumped into the root flares of the tree. This process requires licensed applicators as well as professional pumps and tanks. The cost per tree using macroinfusion is nearly $600; much more expensive than microinjection.
We do not have the capacity to raise the estimated $50,000 per year needed to protect every tree on a three year cycle using macrofusion. We can, however, identify areas where DED has taken a foothold. In those areas, we can selectively inoculate using macroinfusion in an effort to stop the spread to new trees. To do so, we will begin redirecting funds from microinjection to macroinfusion and monitor the results.
Macroinfusion is not a silver bullet. But the latest research and field experience indicates it is an effective protection method. We will use it, microinjection and new scientifically-proven inoculation methods as they become available in an ongoing effort to protect and maintain our beautiful elm trees.