Garden Q&A: On hornets that eat bark and replacing sick shade trees
By Ellen Nibali
Oct 17, 2019 at 7:00 AM
Are these giant Asian hornets? They eat bark off my young river birch. I’m worried it will damage my tree and also I have two small children who play near the tree. I can’t find the nest.
There are no giant Asian hornets in the United States. These are European hornets. Black stripes on the abdomen (as well as on our huge cicada killer wasps) look like the color is dripping.
European hornets strip bark from woody plants (especially lilac) to make their nests and obtain nourishment from the sap. They make papery nests in a cavity, such as a hollow tree or wall void, making them difficult to locate. On rare occasions they make suspended, football-shaped nests like bald-faced hornets do.
Plants typically withstand stripping form European hornets, but there may be some branch dieback when damage is extensive.
These hornets are unusual because they fly at night as well as day, feeding on other insects. Do not attract them by leaving on lights at night. They are not aggressive, but keep your children at a distance as much as you can. Like other social hive-making wasps and hornets, all workers will die with cold weather and the new queens will overwinter elsewhere, never reusing an old hive.
I had to cut down an old white oak in my front yard that developed an armillaria infection. I want to replace it with another shade tree. Do I need to wait for the armillaria fungus to clear from the soil?
With armillaria, if you intend to replant, you need to remove the stump. Armillaria lives on dead wood. Keeping the stump helps armillaria remain in the area, because the stump and remaining root system are a good source of nourishment for it to keep growing.
Have as much of the stump’s wood grindings removed off-site as is possible. Refill the hole with clean top soil. Do not replant in the same hole. Plant your new tree about 30 feet away (or as far as possible.)
It will not matter whether your new shade tree is an oak or other species, as regards the armillaria. However, oaks are the premier species for supporting insects, birds and other wildlife.
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Maryland’s Gardening Experts” to send questions and photos.