A New Zealand statistician has been helping citrus growers in the United States battle a disease which is crippling their industry.
Citrus growers in Florida have been badly affected by citrus greening - a bacterial disease spread by psyllids. It has cost the industry $4.5 billion in lost production in Florida alone.
Otago University statistician Matthew Parry said one of the problems with the classic epidemic disease model was that it was complicated by the understandable response of citrus growers.
"The issue, of course, is that in an orchard setting the growers, once they become aware of the disease, go about trying to prevent it spreading further," he said.
"And in this case that is not only removing infected trees but also spraying against the psyllid to kill it. And that makes figuring out how the disease is spreading much more difficult."
The control model included how to take those control measures into account while still figuring out what was going on with the disease.
"So we want to learn important things about the disease like essentially how far are the psyllids are travelling when they infect trees, at what rate is the infection happening, those kind of parameters which are key parameters for characterising the epidemic," Dr Parry said.
"So once we know those we can actually say what's going to happen next."
He said the psyllid which spread citrus greening had just spread to California, and the adapted model he had helped design was giving growers there a better picture of what was about to unfold.