The best way to control Dutch elm disease (DED) is through good sanitation, which is removing diseased and dying elms and elm wood piles by chipping or burning the wood, so bark beetles do not have a place to lay their eggs. Unfortunately, good sanitation occurs after the trees are already dead or dying.
The only preventative step to keep an elm from getting DED is to inject it with a chemical that prevents the disease from taking hold in the tree.
- If you haven’t considered preventative injections for your high-quality landscape elms, summer is the time period to do so.
- There are some issues that you should consider if you have one or more prominent elms in your yard and are thinking about injection. The tree should be structurally sound and in good health. Does the tree shade a large portion of your yard or the east or west sides of your home, offering potential energy savings in the summer? Does the tree add significant aesthetic and real estate value to your property? Keep in mind there is a financial commitment that must be made every 2-3 years to keep up on the injections necessary to keep the tree protected.
- A chemical is injected into the tree near the base. To do so, an extremely small drill bit is used to make holes around the root flares of the elm. In many cases, small plastic tees are inserted into the holes and then tubing is connected to each of the tees. The tubing will carry the chemical to the tees, which are inserted into the area of the tree that carries water to the upper part of the tree. When the chemical is injected correctly, the tree takes it up into the crown of the tree and it is evenly distributed to give the elm protection against DED transmitted by bark beetles.
- There are two main chemicals used to protect a tree from DED. They are thiabendazole hypophosphite (known as Arbotect) and propiconazole (known as Alamo and other generic brands). In general, the procedure should be conducted by a certified arborist or a plant health care specialist who has been trained and knows how to obtain adequate distribution of the chemical throughout the tree. Additionally, the chemicals are not sold at retail stores.
- The injections can be used therapeutically in certain cases, when the disease is caught very early, and is only effective if the disease infects 5% or less of the tree’s upper canopy. After a therapeutic injection, the diseased branch portion must be removed, plus 5-10 feet beyond the diseased portion. The chemical is not effective if the tree got the disease through shared roots from a nearby diseased elm or if it is present in a branch less than 5 feet from the trunk of the tree. When appropriate, Forestry staff will make residents aware of the possibility of injection before marking a diseased elm for removal on private property. Keep in mind that the disease progresses each day, so timely treatment is necessary to save the tree.
- Most companies offer a warranty or guarantee when they inject a healthy elm, so that if the tree gets DED within the 2- to 3-year protection time period, they will refund your money or re-inject the tree. Each company’s warranty varies so it is important to get the details before you decide on a treatment. Be sure to get quotes from at least two companies and get the warranty in writing so it is clear. Most companies have kept track of their success and failure rates and are willing to share them if you ask. There are several tree care companies who work in Lakeville who offer injection services.