"Unstoppable" Disease Threatens California Citrus

"This is not one more thing, this might be the last thing," said Al Stehly, who manages 200 acres of oranges near Valley Center in San Diego County.

The tiny psyllids are the only transmitters of the disease, officially known by its Chinese name, huanglongbing, or "yellow dragon disease" for its visual effect on leaves. In the U.S., growers call it "citrus greening" disease because fruit fails to ripen.

Psyllids feed on the liquid inside citrus leaves, and once a psyllid eats from an infected tree, it carries the bacteria for life. Diseased trees wither and die within a few years.

More than 22 years of research by the U.S. Department of Agriculture has not yet revealed genetic or biological controls for the disease.

"There is no place in the world this disease is under adequate control," said plant pathologist Tim Gottwald of the USDA's agricultural research service in Florida and one of the world's leading authorities on citrus greening. "We don't have an adequate strategy at this moment."