New method tells growers more about citrus decay

If we know why fruit is dropping, we can better figure out what caused it to drop -- factors such as temperature, wind, humidity, rainfall, citrus greening or other factors, said Wonsuk "Daniel" Lee, a UF/IFAS professor of agricultural and biological engineering.

While there is no known cure for greening, it's important to know its locations and how much damage the disease caused at those sites so growers can mitigate the disease, a new study led by Lee says.

One indicator of the severity of damage is the number of dropped fruit. The other is how much the fruit has decayed once on the ground.

"Daniel and his team are developing methods that will allow a grower to scan many acres to quickly and accurately estimate the severity of citrus fruit drop at any given time," said Fritz Roka, UF/IFAS associate professor of food and resource economics and a co-author in the study led by Lee.

"Unfortunately, greening has exacerbated the degree of fruit drop," said Roka, a faculty member at the UF/IFAS Southwest Florida Research and Education Center in Immokalee, Florida. "Some growers have reported losses of 50 percent of their crop to premature drop. While everyone believes the drop situation is related to greening, we don't have a clear reason why the fruit is dropping."

In the newly published study, Lee and a team of researchers devised an algorithm that helps cameras detect decayed citrus. This research follows a study published two years ago in which Lee found an algorithm to accurately find and count fruit that had dropped from trees in citrus groves.

UF/IFAS researchers are trying to find methods to control the citrus greening disease. A lot is riding on the outcomes of that research. For instance, American growers produced 5.8 million tons of citrus in 2014-2015, down 350,000 tons from 2013 to 2014, according to the U.S. Department of Agriculture. In Florida, the crop is reportedly worth $10.7 billion, according to UF/IFAS researchers.

Lee and his colleagues used their camera equipment to take images of citrus at a commercial grove in Immokalee, Florida. The proposed algorithm improved accuracy of decay compared to previous studies, Lee said.

By estimating citrus fruit drop and creating a fruit-drop map, you can create citrus management strategies specific to certain locations. For example, growers can implement better fertilization and irrigation programs that can help treat greening-infected trees to delay tree death and prevent tree infection.

The machine vision system demonstrated it could be further redeveloped into a real-time system for use in commercial citrus groves, Lee said.

Findings from the study are published in the journal Computers and Electronics in Agriculture.