In our study kaolin particle films helped manage pests, and also improved tree growth. Kaolin particle films are a type of mineral that can be sprayed on plants to create a protective layer. Asian citrus psyllids, the pest that transmits citrus greening disease (HLB), are attracted to the natural color of leaves and the particle films cover this. White and red colored particle films were used in this study. Trees with white and red dye had a greater growth rate of trunk girth than controls, regardless of infection. This study found that particle films helped reduce the number of psyllids on leaves, as well as increased tree growth under HLB pressure.
HLB is the current largest threat to the Florida citrus industry; citrus production has declined, and citrus trees are nearly all infected. HLB stunts tree growth and limits yield, especially if infection occurs when the trees are still small. We studied for three years whether kaolin particle films on newly planted trees could help manage psyllids. We also tracked tree growth response to particle films and HLB.
HLB reduces the growth rate of trees and negatively affects fruit yield and other quality characteristics. HLB cannot be cured once trees are infected so pest control is the usual course of action when it comes to preventing infection. HLB is spread when adult psyllids carry the bacterium from infected trees to uninfected trees. Kaolin particle films are a potential alternative to insecticides as a way to manage psyllids and the reduction in tree growth caused by HLB.
Increased growth in treated trees happened in spite of HLB infection. The positive impact of particle films on growth is likely due to shading, reducing photoinhibition, and light redistribution to lower canopy layers. Kaolin treatments increased growth enough that they made up for the loss in growth from infection. This is promising because it helps relieve pest pressure, while increasing growth of HLB affected trees.
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.
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.”
Talent Vharachumu was an undergraduate intern who is originally from Zimbabwe and attends university in Costa Rica. She is studying agricultural sciences and has become particularly interested in plant physiology, especially due to her time at the lab. Along with the work Talent did for the physiology lab, as is typical for an intern, she sometimes participated in work with other labs as well. She enjoyed this because it allowed her to learn many different things and meet more people. She hopes to be able to return to the lab to complete her masters.
She enjoyed her work at the lab because she learned more about plant physiology. Our goal at the tree physiology lab is to improve general tree health and make strides in understanding tree physiology better and more completely. To accomplish this goal, we do research with a whole plant approach. One such experiment is on how different plants respond to and are affected by heat.
Talent primarily worked on that experiment. She would collect leaves from a variety of trees in a variety of genotypes and perform a procedure on them to test how they tolerate the different temperatures. To do the experiment she used a machine that punches a piece of the leaf out, then placed the piece on a black disk that went inside a Ziplock bag, which was then placed in a container of water for 30 minutes. Then she’d record the chlorophyll fluorescence (photosynthetic energy conversion) of the leaves, given from a machine called the Fluoremeter. She also worked on another project with an infrared gas analyzer (Li-6800) machine to measure photosynthesis, gas exchange, and chlorophyll fluorescence.
When I asked Talent why she believes this work is important and why she thinks people should care about it she explained that the data she’s gathering helps us better understand the way climate change is affecting the planet, different environments, and plants in general. People who work in agriculture can use the data about which plants tolerate heat better to determine which genotypes to grow, which hopefully will increase plant yield and agricultural efficiency as temperatures warm. Talent also said it “…can help them reduce losses from low production due to high temperatures that are being caused by global warming.” This is useful because it allows growers to make informed decisions about what kinds of crops to plant as the climate and planet continue to change. I asked specifically what she would say to people who think they don’t have a reason to care about plants and she said, “They don’t care about plants, but they care about eating.”