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Particle Films as a Deterrent for Insect Pests

For the past 90 years, growers have utilized particle films to deter insect and mite feeding on horticultural crops.

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Updated:

June 12, 2024

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Figure 1: Particle films act as physical and visual deterrent for a variety of insect pests. Photo by Thomas Ford, Penn State

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Kaolin clay, marketed as Surround WP, is the primary product utilized by growers today to protect crops from arthropod infestations and feeding injuries. To be effective, a particle film must have the following properties:

It must be chemically inert.
Particle diameter must be <2 µ
It must be formulated to spread to create a uniform film over the leaf surface.
The film must be porous so that it does not interfere with gas exchange from the leaf.
The film must transmit photosynthetically active radiation (PAR) but excludes ultraviolet (UV) and infrared (IR) radiation to some degree.
The film must alter insect/pathogen behavior on the plant that is being protected.
The film must be able to be physically removed from harvested commodities.

Particle films deter insect feeding through various mechanisms, including reflected light, mineral barriers, and the toxic properties of the particle film that has been applied. Researchers have long held that insects like aphids were repelled by highly reflected surfaces (Moericke 1952, 1955; Kring 1962, 1964). Research from Dr. D. Michael Glenn and Dr. Gary J. Puterka revealed that particle films can have significant effects on insect behavior that were not previously recognized by other researchers. Their research also demonstrated that particle films repelled various insects that were not previously known to be repelled by reflected light.

Particle films have proven effective against many key orders of arthropod pests affecting crops, including homopterans, coleopterans, lepidopterans, dipterans, and rust mites. Arthropods utilize all their senses when locating and accepting plants as hosts for feeding and reproduction (Miller and Strickler 1984). When an insect is exposed to positive cues (touch, taste, sight, and smell), it will exhibit acceptance behavior and begin feeding or oviposition. If a particle film is present and the insect's touch, taste, sight, and smell are adversely impacted (negative cues), repellency or deterrence may be noted.

Organic growers have frequently adopted particle film technologies to protect their crops from insect injury. Striped cucumber beetles are a known vector of bacterial wilt and are a major cucurbit pest in the Mid-Atlantic region. Growers wishing to use a particle film like Surround WP should spray their crop twice a week early in the season to deter striped cucumber beetle. Kaolin clay is white in color, and when it is sprayed on plants, it will leave a white or chalky film on the leaf and/or stem surfaces that will reflect light and impact visual cues while providing a protective barrier against insect feeding and oviposition.

Organic tree fruit growers can also utilize particle films to deter insect infestations in fruit crops. An organic fruit grower in my area applies Surround WP weekly to their orchard to deter Japanese beetle feeding. Trees protected with Surround WP are almost beetle-free, while adjacent unsprayed trees with no residue are almost completely defoliated.