The U.S. Department of Agriculture has confirmed citrus greening in Savannah, Ga., bringing to four the states in which the lethal citrus disease has been found.

The positive sample came from a mature sour orange tree on a residential property near where Asian citrus psyllid had been found in August 2008. The disease was found when inspectors paid a follow-up visit to the property, according to a pest alert.

The USDA's Animal and Plant Health Inspection Service is investigating the source of the tree.

The USDA is working with the Georgia Department of Agriculture to develop a quarantine in the area.

Earlier this year, greening, also known as huanglongbing or HLB, was confirmed on a residential property in Charleston, S.C.

Last year, it was confirmed in residential trees in three separate Louisiana parishes.

Citrus greening is harmless to humans but can kill a citrus tree in a matter of a few years once it's infected.

For more information on citrus greening, visit the University of Florida's citrus greening database.