University of Florida researchers have created a mathematical model that shows how citrus greening is transmitted within an infected tree — an important step toward helping scientists understand the devastating disease.

The model, published this month by the journal Proceedings of the National Academy of Sciences, revealed that once a tree is infected, insecticides to control the pests that spread the disease may not be enough to halt the disease’s progression in the tree, and instead may only slow its spread within the tree.

Removal of obviously diseased new growth, called flush, or shoots, is not a solution either. The model shows that even without showing symptoms, many shoots may already be infected so that infection of other parts of the tree can continue.

(For more, see: Scientists closer to HLB solutions in citrus)

Citrus greening, known to scientists as huanglongbing, or HLB, was first detected in Florida in 2005.

The disease was discovered in a backyard citrus tree in Los Angeles earlier this year and now threatens California’s citrus industry.

Greening has cost Florida’s economy an estimated $3.63 billion in lost revenues since 2006 and poses a huge threat to the state’s $9 billion citrus industry, the nation’s largest. It weakens and eventually kills infected trees.