Location: Subtropical Plant Pathology Research
Project Number: 6034-22000-042-004-N
Project Type: Non-Funded Cooperative Agreement
Start Date: Aug 1, 2015
End Date: Aug 1, 2020
Objective:
Develop one or more methods using water or air, heated by direct sunlight, and apply this heated water or heated air to the tree in specific areas, i.e., trunk and main scaffolds, thus removing the possibility of damaging excess foliar material, but still negatively affecting the bacterial pathogen survival. With minimal damage to the tree, we anticipate a short recovery time, low impact to the grower, and tree recovery to a productive state.
Approach:
1) Hydro-solar thermotherapy: Firstly, the hot water is provided by three (3) solar heater coils, hooked up in parallel, each holding approximately 40L of water. From these coils hot water is pumped to “water jackets” around 5 trees hooked up in series. Water is cycled form one coil to the next to maintain maximally heated water in the system. The electrical demands of the system (pump, valves, etc.) are minimal, and are handled by an on-board SLA battery, which is being kept charged by onboard solar panels. Capacity is dependent on volume. The coil around each tree and plumbing between trees contains ~0.15 to 0.20 gal of heated water. Each coil system contains approx. 11 gal of water, and can therefore tree 54 to 71 trees. By chaining multiple coils in series the potential increases to treating 100s of trees simultaneously.
2) Hydro-solar thermotherapy via alternating heat and cold: The second system is based on a single solar heater coil collecting heat, and a second coil that is “cool” water (ambient or less). This is being done to test if cycling back and forth between hot and cool water will add additional stress to the CLas bacteria, more stress than can be achieved by heating alone. To test this, the second coil (composed of copper pipe) will be buried in the ground near the trees (in a more real world application, cool water could be provided from the plant watering system). Burying the coil in the ground will act as a cooling sink as the soil temperature rarely gets above 70°F.
3) Parameter estimation: This series of experiments are designed to define citrus tree heat tolerance via trunk application of a series of increasing temperature regimes and thereby optimize the heat tolerance parameter. With this system, heat can be added to the tree in a regulated, controlled method, so that temperature and duration of the hot water can be determined. To accomplish this, the system will be comprised of an on-demand hot water heater (also known as a “tankless” hot water heater), and feedback temperature control system, so that the water temperature going to the tree remains constant for a given period of time. Once we determine how much heat and for how long a tree can tolerate, we can better apply an optimal “in-field” system.
