Huanglongbing (HLB; “citrus greening disease”) is currently the biggest threat to the Florida citrus industry. HLB has caused declines in citrus production and has infected trees at a rate of 100%. Insecticides reduce Asian citrus psyllid, the pest that transmits HLB, but they don’t prevent more psyllids from moving into the planting, and they often kill the pest after transmission. This is why growers need non-insecticidal prevention options. One of these options is to apply kaolin particle films on trees to help manage psyllids.
Kaolin particle films cover the natural color of the plants, which is what ACP are attracted to. White kaolin was already known to reduce ACP, but this study tested whether red kaolin may also help mitigate ACP. ACP are attracted to the blue and ultraviolet light in the leaves and red was thought to further reduce this. We made the kaolin red by taking naturally white kaolin and mixing in a dye and a binding agent, resulting in a pinkish color.
This field study tested the effect red and white kaolin particles had on ACP pressure over the course of two years. The particles were added to the leaves of young non-bearing Hamlin trees. Another set of trees were treated with foliar insecticide and one control set received no treatments.
Overall, trees with red kaolin had the lowest number of ACP. Trees with white kaolin had less than the trees with foliar insecticide. The control trees had the most ACP. Important to note, none of the kaolin treatments completely prevented ACP from infecting trees but merely slowed the infection down. The onset was slower in red trees than white. These findings indicate that kaolin particle films may be an alternative pest management to foliar insecticides when it comes to reducing ACP and slowing HLB infection.
Here Monique Rivera, entomologist at UC Riverside, and Christopher Vincent, physiologist at UF, discuss using particle films in citrus management. At some point I make a particularly effusive gesture, and smack my fancy microphone and lose sound for a minute. What can I say physiology is just too exciting to keep my hands down!
Mark Keeley turned a lifelong passion for plants into work that hopefully will help us better understand the way HLB affects Florida citrus trees. He worked in citrus research before starting his Master’s, but said he’s always been interested in plants and has been playing around with them for as long as he can remember. He made his way to plant research after trying out several undergrad degrees that didn’t fit quite right. Eventually, to no one’s surprise he told me, he joined the UF Horticultural Sciences Department. From there he had several jobs before landing one at a private agricultural research station. He likes his job because he said it’s, “Me and orange groves 4 or 5 days a week. Me and the plants, it’s quiet. Calming.” Through this job he decided to pursue a Masters in Agronomy. When asked why he’s pursuing his masters and working full-time for the private lab he laughed and said it was mostly for selfish, personal reasons. As a part of his master’s program he’s working with the tree physiology lab on a project that’s attempting to show a relationship between photosynthesis and citrus greening.
At the tree physiology lab, we hope to improve citrus growth based on understanding its environmental physiology. This particular experiment’s goal to describe the effects of HLB on photosynthesis. Part of this experiment also includes looking at the difference between shoot photosynthesis and leaf photosynthesis. This photosynthetic activity can’t be translated between leaf and tree, so we are trying to determine why. Studying photosynthesis on the leaf level can help garner understanding for the effects of photosynthesis on the whole canopy, but we need to understand what causes differences, too. Mark explained, “[We are] specifically looking at impacts of greening on photosynthesis as well as the amount of photosynthesis acquired from the leaf material and the stem material and what those impacts are over time on maturation.” In terms of the importance of this work for management, “It’s no longer preventing the bacteria from being there; it’s more how do we support the tree in [spite] of the bacteria,” he explained. This would be helpful because Mark believes the current approach to managing HLB isn’t working, so this could open the door to try other approaches.
The project uses an infared gas analyzer (affectionately called “IRGA”) called Li-Cor 6800. The machine cycles a known amount of CO2 and water over the leaf and measures how the concentrations change after they pass over to determine how much CO2 is being taken in and how much water is being released by the plant. This allows us to measure photosynthetic activity. Doing this in the lab with a known amount of light allows us to see the direct impacts of disease or other treatments over time without having to contend with clouds, different radiation intensities, etc. Eventually Mark would like to do work like this in the field, but while he’s still developing the methods, inside the lab is the best opt
The project uses an infared gas analyzer (affectionately called “IRGA”) called Li-Cor[RV1] 6800. The machine cycles a known amount of CO2 and water over the leaf and measures how the concentrations change after they pass over to determine how much CO2 is being taken in and how much water is being released by the plant. This allows us to measure photosynthetic activity. Doing this in the lab with a known amount of light allows us to see the direct impacts of disease or other treatments over time without having to contend with clouds, different radiation intensities, etc. Eventually Mark would like to do work like this in the field, but while he’s still developing the methods, inside the lab is the best option.
When I asked why he believes this work is important he said, “Fascination for me. I keep going down the rabbit hole more than anything. I think it will be important if we find some of these relationships with the infection level and the tree. Like I said, it’ll change the way we culturally try to manage the disease [HLB]. Other than that, it’s more of a curiosity.”
Citrus Tree Physiology Lab 