If you find ants on your magnolia tree, should you be concerned? Yes. Ants do not eat wood, even magnolia tree wood, but there are other features magnolia trees have that can attract ants. Any species of ant can be found on magnolia trees. But the most commonly seen species are the carpenter ants, which are larger than most other kinds of ants.
Many species of magnolia trees attract a parasite commonly called scale. These insects attract ants and even wasps because they secrete sweet honeydew-like liquid which the normally carnivorous ants and wasps enjoy drinking. In order to get more of the drink, the ants will let the magnolia scale live but will kill other insects on the tree.
Significance
Magnolia trees with noticeable populations of ants need checking further. The ants are either attracted to the honeydew from magnolia scale or they are trying to find a home in dead wood for their colonies. Ants cannot directly kill a magnolia tree, but they are quick to exploit any decaying or dead parts of the tree.
Carpenter ants in particular will tunnel into dead wood, causing the entire tree to become weaker and weaker until whole limbs may fall off. According to the Texas Agricultural Extension Service, magnolia trees often have knots that contain decaying or weakened wood. Carpenter ants can set up colonies in the knots.
Magnolia scale is not that great for a magnolia tree, either. According to the University of Wisconsin, a tree heavily infested with magnolia scale can eventually die.
Treatment
If you are unsure what species of ant is crawling about your magnolia tree, please contact an exterminator. The only species that need exterminating are carpenter ants because of their tunneling habits. Carpenter ants can be treated with insecticides like rotenone that is placed directly into their colony. Colonies can usually be located by the presence of frass or ant droppings being shoved out of a hole in the tree by ants.
Other species of ants and even wasps are only hanging around the magnolia tree because they want to drink the sweet liquid secreted by the magnolia scale. Removing magnolia scale parasites will also get rid of the ants. However, treating magnolia scale can be tricky. The University of Kentucky recommends pruning any branch that is heavily infested. This action may save the whole tree because the tree will not be spending any energy on trying to keep the infested branch alive.
Insecticidal soaps have proven effective for only the newly hatched magnolia scale. But larger magnolia scale can be killed naturally with ladybugs and predatory mites. If the tree is heavily infested, contact an exterminator to bring in heavy-hitting insecticides like pyrethrins.
References:
Texas Agricultural Extension Service. “Carpenter Ants.” http://insects.tamu.edu/extension/bulletins/l-1783.html
University of Kentucky. “Magnolia Scale.” http://www.ca.uky.edu/entomology/entfacts/ef431.asp
Rhode Island Cooperative Extension. “Carpenter Ants in Trees.” http://www.uri.edu/ce/factsheets/sheets/carpanttrees.html
University of Wisconsin Extension. “Magnolia Scale.” http://www.uwex.edu/ces/wihort/gardenfacts/XHT1154.pdf
