Particle Films
While there is currently no cure for HLB, several management practices have been developed to improve the health of infected trees. Kaolin particle film is one such practice. It does not cure HLB, but it helps create a more favorable canopy environment for affected trees. Imagine a sick person walking in the hot summer of Florida. Now give that person an umbrella. It will not cure their sickness but it reduces exposure to heat and sunlight, allowing the body to function better, making them healthier and less physically stressed. Kaolin works in a similar way for citrus trees.
Kaolin clay is a naturally occurring white mineral. When mixed with water and sprayed onto trees, it forms a thin particle film that coats leaves and fruit. Originally, kaolin was used as pest repellent, as the white coating makes it difficult for insects to recognize their host plants. Over time, researchers discovered additional benefits kaolin particle film related to temperature regulation and light management.
Benefits of Kaolin Particle Film
- It reduces psyllid pressure by interfering with insect host recognition.
- It shades the outer canopy, lowering leaf temperature by about 7 degrees and reducing water loss from leaves.
- It reflects sunlight to the inner canopy, helping shaded leaves contribute to tree growth.
With lower leaf temperature, trees lose less water through transpiration. This improves overall plant water status and allows the tree to function more efficiently. Better water status supports photosynthesis and may help the plant move food (sugars) from leaves to fruit and roots, even when phloem function is partially compromised by HLB.
Learn more:
- Reduce HLB Pressure and Enhance Growth With Kaolin
- Kaolin Clay May Be Viable Option to Protect Citrus Trees from ACP
- Keeping Cool with Particle Films
- Kaolin Helps With ACP and HLB
- Red and White Kaolin Particle Films Enhance Growth and Yield of HLB-infected Sweet Orange Trees
- White and red-dyed kaolin particle films reduce Asian citrus psyllid populations, delay huanglongbing infection, and increase citrus growth
- Particle Films as a Deterrent for Insect Pests
Kaolin is naturally white but can be mixed with dyes. In previous studies both white and red-dyed kaolin have shown increased canopy growth, yield, and fruit quality. However, in ongoing UF/IFAS field project, red-dyed kaolin has not consistently improved performance and, in some cases, has been associated with higher fruit drop and lower yield compared with untreated trees. Based on these results, red-dyed kaolin is not currently recommended to include in grove management practices.
Figure 1: Coverage of and white kaolin particle film on citrus leaves after application.
Application Rates (Based on UF/IFAS Research)
Ongoing research at the UF/IFAS Citrus Research and Education Center (CREC) in Lake Alfred on Hamlin sweet orange has shown that lower kaolin rates than the labeled rates often perform better. 12 lb of Surround WP per acre was associated with higher yield and Brix and lower fruit drop compared to higher rates.
Figure 2: Comparison of high-rate (left) and low-rate (right) applications of white kaolin particle film on citrus trees. The lower rate results in a lighter, less visible coating but has performed best, with higher yield and Brix and reduced fruit drop, and is therefore the recommended application rate.
How to best apply particle films
The goal in applying particle films is even coverage, both over time and over the outside of the canopy. Maintaining consistent particle film coverage is important to achieve the full benefits of kaolin applications. To achieve good coverage small droplet size is ideal, and the volume of application should be small enough to minimize beading on the surface of the leaf. To maintain coverage, it is important to prevent the kaolin film from being washed off by rain and to ensure that new leaves also remain protected.
Rainfast application
Raynox Prime is an emulsified wax product that improves kaolin adhesion to leaf surfaces. When kaolin is mixed with Raynox Prime, the particle film is more resistant to wash-off from rainfall. Always make sure to apply when the product will have time to dry before a rain. When Surround WP and Raynox Prime are applied together and are allowed to dry, there is very little wash off in rain, and the product will adhere to the leaves for several months.
- White kaolin:
12 pounds of Kaolin + 12 pounds of Raynox in 100 gallons of water per acre (approximately half the label-recommended rate for Surround WP)
Application timing
Under these conditions, reapplication is generally only needed following the expansion of a new flush. Citrus trees produce new major flushes three to four times per year, so kaolin should be applied after new leaves are fully expanded. Applying kaolin too early will leave new growth unprotected.
|
Application |
Timing |
|
First |
After expansion of spring flush |
|
Second |
After expansion of summer flush |
|
Third |
After expansion of fall flush |
A fourth application may be required if additional flushes occur.
Application Tips
- Use an air-blast sprayer for good canopy coverage.
- Set spray pressure to >150 psi to produce fine droplets that evenly coat leaf surfaces.
- Operate the tractor at a slow speed (~3 miles per hour) to reduce drift and improve spray deposition on leaves.
- Avoid spraying when:
- Wind speed exceeds 7 mph
- Rain is expected during or shortly after application
- Check the weather forecast before spraying.
- Adjust valve settings to distribute spray evenly throughout the canopy.
- Maintain continuous tank agitation to keep kaolin particles suspended. Without agitation, particles settle at the bottom of the tank, resulting in clogged lines and uneven application.
- After each application, empty and thoroughly rinse the spray tank and lines. Leaving kaolin residue in the system can clog nozzles and lines.
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