Inexpensive Vision Sensor Detects Citrus Greening

While a commercially available cure for crop-killing citrus greening remains elusive, University of Florida researchers have developed a tool to help growers combat the insidious disease: an efficient, inexpensive and easy-to-use sensor that can quickly detect whether a tree has been infected.

That early warning could give growers enough lead time to destroy plagued trees and save the rest.

“The current ground inspection is very time-consuming, subjective, and labor intensive, and also requires a lab analysis of leaf samples,” said Daniel Lee, a UF professor of agriculture and biological engineering who developed the sensor. “Our real-time, in-field detection system can provide objective, fast, and accurate results of the disease detection.”

Scientists have been unable to find a cure for citrus greening because infected plants are difficult to maintain, regenerate and study. But UF/UFAS researchers relied on the fact that citrus greening causes leaves to store high levels of starch that can rotate the direction of reflected light from its original orientation in the development of the sensor.

In 95 to 98 percent of laboratory and field tests, the sensor accurately detected the signs of citrus greening: leaves with veins and splotches that appear a pale shade of gray on the sensor’s images, an obvious contrast to the dark-gray image of healthy leaves.

UF/IFAS researchers used 10 high-powered LEDs and an inexpensive camera to assemble the sensor for a cost of less than $1,000, making it affordable for even small citrus growers, although commercial availability depends on finding a sponsor, Lee said.

Citrus greening, also known as “yellow dragon disease,” begins when a tiny sap-sucking insect deposits bacteria on the leaf of a healthy fruit tree. The bacteria invade the tree and starve it of nutrients, causing its fruit to be shrunken and misshapen with a thick, pale peel that remains green at the bottom. Most trees afflicted with citrus greening die within a few years.

First described in China in 1929, citrus greening was only recently detected in North America. In Florida, one of 10 states that have been quarantined due to the presence of the bacteria-carrying insect, commercial citrus acreage decreased by 28 percent from 2004 to 2011, with greening one of the major reasons for this loss.

While pursuing early detection methods that lead to the removal and destruction of infected trees to control the spread of citrus greening, UF/IFAS researchers are working to wipe out the disease on a number of fronts. Among them are eradication of the bacteria-carrying insect that causes the disease and breeding citrus rootstock that show better greening resistance.

A UF/IFAS study on the vision sensor appears in this month’s issue of Computers and Electronics in Agriculture. Contributors to the report in addition to Lee include Alireza Pourreza, a postdoctoral research associate in UF’s Department of Agricultural and Biological Engineering; Reza Ehsani, a UF associate professor of agricultural and biological engineering; John K. Schueller, a professor in UF’s Department of Mechanical and Aerospace Engineering; and Eran Raveh, a researcher at the Agricultural Research Organization in Negev, Israel.