More than four acres of Willow Trees have died off in the Elfin Forest, and the culprit is a mystery.
Officials with the Escondido Creek Conservancy noticed black leaves and rotting stumps in the spring. Tests at UC Riverside have ruled out the Shot Hole Borer Beetle, which has wiped out Willows by the hundreds of thousands in the San Diego area.
Scientists say the area at Questhaven and Harmony Grove roads is "ground zero" for the infestation.
In early August trails were closed to prevent any kind of potential spread.
"We are telling people to make sure their dogs are leashed and do not take any kind of wood from the area, that contributes to the spread," said conservancy board member Leonard Wittwer. "This is very disconcerting."
While the cause is still a mystery, initial tests found a fungus called Phaeoacremonium. According to Wittwer, the fungus is not believed to be harmful to humans.
Wittwer says tests conducted Friday will be completed in seven to 10 days.