The university said in a statement Wednesday that a herbicide commonly used to kill trees was applied "in lethal amounts" to the soil around the two trees, and that they likely can't be saved.
Auburn discovered the poisoning after taking soil samples on Jan. 28, a day after a man called a syndicated radio show based in Birmingham saying he had used the herbicide on the trees.
"The weekend after the Iron Bowl, I went to Auburn, Ala., because I live 30 miles away, and I poisoned the Toomer's trees," the caller told The Paul Finebaum Radio Show, saying he was at the Iron Bowl.
Calling himself "Al from Dadeville," he said he used Spike 80DF, also known as tebuthiuron, and the trees "definitely will die." The caller signed off with, "Roll Damn Tide."
Auburn fans traditionally celebrate by using toilet paper to roll the Toomer's Corner trees, which are estimated to be more than 130 years old.
"We will take every step we can to save the Toomer's oaks, which have been the home of countless celebrations and a symbol of the Auburn spirit for generations of Auburn students, fans, alumni and the community," university President Jay Gogue said in a statement.
City police are investigating the incident. The use of Spike 80DF is also governed by state agricultural laws and the Environmental Protection Agency. The university said it doesn't use the herbicide.
"We are assessing the extent of the damage and proceeding as if we have a chance to save the trees," said Gary Keever, an Auburn University professor of horticulture and a member of Auburn's Tree Preservation Committee. "We are also focused on protecting the other trees and shrubs in Samford Park. At this level the impact could be much greater than just the oaks on the corner, as Spike moves through the soil to a wide area."
A small group gathered and rolled the trees Wednesday afternoon.
The soil samples were tested at Mississippi State.
The amount of herbicide detected in four samples ranged from 0.78 parts per million - described by Auburn as "a very lethal dose" - to 51 parts per million.
"This herbicide is extremely active and persistent," Keever said. "It's very likely to be in the soil for 3 to 5 years."