Mobile Batch Heat Treatment System for Treating HLB-Infected Citrus Trees

摘要

Citrus production in Florida is devastated by citrus greening disease, also known as HLB. The HLB is a phloem-limited bacterial disease of citrus, and currently, there is no known cure for it. Previous research has shown that heat treatment slows downthe progress of this disease and increases the production life of HLB-infected trees. The objective of this research was to develop a mobile heat treatment system using steam to heat treat individual small- to mid-sized HLB-infected citrus trees under field conditions. The mobile heat treatment system consisted of a tree-covering enclosure system attached to a citrus hauling truck, a portable steam generator, a water tank, a water supply pump, and an electric generator. The tree covering enclosure system was built in a reverse U-shape frame attached to the side of the truck and was hydraulically operated. The frame was covered by a relatively heat-resistant opaque plastic tarp to completely cover an area of about 14 m3 in volume. The steam was supplied from a diesel-operated portable steaming generator, which was loaded on the back of the hauling truck. The inside temperature of the tree enclosure was monitored using four thermocouples and a data logger. More than 1600 trees of different varieties and ages were treated in more than 10 different locations. Trees were steamed at different temperatures and for different durations. It took about 25 to 30 s to hydraulically unfold the tent and cover the tree, fold it back, and move to the next tree. However, raising the air temperature within the tent to about 60°C took 60-90 s depending on the ambient temperature and wind speed. The treatment duration was between 0-6 min. The apparatus is simple in design and efficient for field use. However, the long-term effect of heat treatment is still under investigation.