You have always been grateful that some species of elm trees are not susceptible to Dutch elm disease, which has decimated so much of the elm population. Now, however, you've heard about a more recent threat that could cause serious problems for your trees – an insect known as the European elm scale. How can you know whether your elm trees are infected with this insect, and what are the possible solutions?
About European Elm Scale
Scale insects are tiny bugs that feed on leaves and branches. European elm scale insects tend to live high up in the small branches of trees. People typically don't realize the tree has an infestation until symptoms of damage develop. Even if the tree is small and the bugs are on branches at eye level, they just look like little dark bumps with white fuzz.
If one of your elm trees has a scale infestation, you'll see patches of yellowing leaves, sometimes in seemingly random places. Some leaves may look as though they've turned black; that's because the bugs excrete a sticky material that tends to develop sooty mold on it. That sticky material is called honeydew. It's very sweet, so it attracts ants, bees, wasps and hornets. It also drips from the tree and lands on vehicles, lawn furniture and other objects underneath. It takes some elbow grease to get that substance off cars and furniture, since it's similar to sap.
In addition, you'll notice leaves falling during the summer and branches that are dying, typically toward the top of the tree.
Depending on the size of your affected elm, tree service technicians may tackle the problem with a hose and a brush. This is only feasible on younger, relatively small trees. Tree service technicians typically do not spray insecticide on affected elms since the spray tends to drift to other plants, where it kills helpful insects as well as harmful ones. For instance, drifting spray will kill lady beetles that eat elm scale insects.
Instead of spraying pesticide, the technician may apply a smothering horticultural oil or inject your infested elms with an insecticide for a targeted approach. He or she may also apply insecticide at the base, where it soaks into the ground and the roots absorb it. From there, the tree takes it up into the branches, twigs and leaves, where it may eliminate or at least significantly reduce the population of the bugs as they chew on these materials.
The actions of the European elm scale negatively affect the beauty of the tree, but they often don't endanger its health to any great extent. However, if the elm had already been weakened for any reason, or if the infestation grows large enough to do a lot of damage, elm scale bugs may eventually kill the plant.
A professional tree service can safely remove dead trees from your property. Technicians also can advise you whether any weak, sick or damaged trees should be removed as well. This often is a good safety measure if the trees pose a danger of falling. Sometimes cutting away a large branch or two can restore the tree to better health.
In some cases, treating an elm scale infestation is not entirely effective, as it can be difficult to eradicate an established population. The ongoing problem with honeydew can be aggravating. You have the option of asking the tree service technician to cut down and remove the trees.
Tree service technicians know which pesticides are most effective for battling European elm scale, the best times of year to use them and how to apply those substances. They also know when it's best to remove trees to prevent dangerous incidents and to prevent bugs from infiltrating other elms. Contact a professional tree service if you see any signs of infestation by European elm scale insects.