Dutch elm disease is difficult to control and, without proper management, it will wipe out a large population of elms in just a few years. However, with a properly implemented management program, the devastating effects of the disease can be reduced greatly.
An effective Dutch elm disease management program includes four parts for control:
- Prompt detection and removal of diseased elms
- Disruption of root graft transmission
- Saving diseased elms
- Protecting high-value elms with Arbotect
1. Prompt detection and removal of diseased elms
Scouting for Dutch elm disease and identifying diseased elms is the first step of any DED management program. Scouting also involves checking peoples’ yards and garages for elm wood. Scouts will usually move through an area every 2-4 weeks during the growing season to make sure dying trees are identified and properly dealt with.
Promptly removing and disposing of elms dying from Dutch elm disease is the key to effectively managing Dutch elm disease on a community-wide basis. It involves identifying diseased elms that cannot be saved by tracing and immediately removing those trees. This will reduce the number of disease carrying beetles. A single dead elm can produce tens of thousands of contaminated beetles. Without such a program, a substantial majority of a community’s elm population will succumb to Dutch elm disease and die within a few years. Removed elms need to either have their bark removed, be chipped, burned, or buried.
2. Root Graft Prevention
Severing grafted root systems between diseased and healthy elms can save many trees. Accordingly, prompt disease detection as well as installing root graft barrier trenches is very important to the overall success of an integrated control program.
The only way to stop the spread of Dutch elm disease through root grafts is by physically breaking the root connections between the infected tree and the healthy tree. This is most often accomplished with trenchers or vibratory plows. In situations where there are buried utilities, an Air Spade can be used to remove the soil and expose the root grafts without damaging the utility lines. Trenches should be at least 3 feet (1m) deep in clay soils and 5 feet (1.5m) in sandy soils, although it is always best to go as deep as your equipment allows.
Trenches are typically installed midway between the infected tree and the healthy tree, although this can be adjusted in either direction depending on how far the infection has spread. It is important to know where the fungus is located in the diseased tree before the trench is installed. If the disease stain is already at ground level in the infected tree it is impossible to determine how far it has traveled through the root system toward the healthy tree, so a second trench may be necessary. This trench would isolate the healthy appearing tree from any others that might be root grafted to it.
It is important to sever the root grafts before removing the diseased tree. Because each tree is transpiring, removal of the diseased tree must allow the healthy tree to pull all of the moisture and fungal inoculum out of the other tree’s root system quickly. An Air-Spade can be used to remove soil and expose root grafts in situations where utilities are present.
3. Saving Infected Elms
Tracing is a method of saving elms recently infected with Dutch elm disease. It is far more cost effective than removing and replacing an elm. By utilizing this procedure, a city can save many thousands of dollars. Since the fungus that causes Dutch elm disease grows very predictably in a narrow band downward and only in the current year’s water-conducting vessels, tracing is easy to learn and incorporate for a qualified arborist.
4. Protecting High-Value Elms with Arbotect
There have been hundreds of proposed “cures” or protection products for Dutch elm disease over the years, but only one treatment has been proven to work through replicated University trials. When applied properly, Arbotect provides a 99% success rate against Dutch elm infection for up to 3 years.
Arbotect does not work if the tree already is infected with Dutch elm disease or if the disease fungus enters the tree via root grafts.