Kaolin is naturally occurring clay resulting from weathering of aluminous minerals such as feldspar with kaolinite as its principal constituent (ATTRA 2004). Kaolin is a common mineral used as an anti-caking agent in processed foods and an additive to cosmetics, toiletries and health products. It is also used as an “inert” carrier in some pesticides, and enhances the performance of some microbial products (Rasad and Rangeshwaran, 2000). Its use is permitted in organics, being considered non-synthetic. Kaolin is ground and processed further to reach a uniform particle size for application as a plant protectant. Applied in suspension in water, kaolin produces a dry white film layer of interlocking microscopic particles on the surface of leaves, stems and fruit after evaporation of the water.
How it works: Kaolin material has several modes of activity (Stanley 1998). Kaolin acts as a physical barrier preventing insects from reaching vulnerable plant tissue. It acts as a repellent by creating an unsuitable surface for feeding or egg-laying. The uniform white film may also disrupt the insect’s host finding capability by masking the color of the plant tissue. Furthermore, particles of kaolin act as an irritant to the insect. After landing on a treated surface, particles of kaolin break off and attach to the insect’s body triggering an excessive grooming response that distracts the pest.
It was originally developed for pest control, because the film mechanically hampers pest suction, but the different light signature of the reflected light also causes insect avoidance for many pests. In viticulture, kaolin has been proposed to control the diffusion of Pierce’s disease. Kaolin films not only reflects photosynthetically active and ultraviolet radiations, but also infrared, thus lowering temperatures of sprayed organs. (See Kaolin and Climate Change).
Kaolin formulations have also been shown to suppress diseases in greenhouse and field studies (Haggag 2002, Puterka et al. 2000, Glenn et al. 1999), and to kill insects in stored grain (Mostafa and Al Moajel 1991). Labeled products for these purposes are not currently available in the US.
The use of Surround® (a trade name for kaolin clay) can increase overall fruit yields in regions with high light and temperature levels (Puterka et al. 2000). In these situations, it can act as an anti-transpirant, reducing stress on the plant. Surround® has caused both yield increases and decreases in vegetable trials (Maletta et al. unpublished). In eggplant, it reduced marketable yields and plant growth, while in potato it increased yields of ‘Superior’ but not ‘Norland’ variety, even though it had no effect on potato leafhopper levels.
Formulation & application guidelines: Kaolin clay is available as a wettable powder to be mixed with water. Application can be made with most commercially available spray equipment but large amounts of water are required. To prevent caking, it is suggested that the material be added while mechanical agitation is running, or to first completely mix the needed amount in a small amount of water before filling up the tank to the recommended volume. It may be tank mixed with soaps, and most pesticides, but not copper, sulfur, or Bordeaux mixtures. Precipitation, curdling, uneven film formation or changes in viscosity are signs of incompatibility (Engelhard 2001). Periodic shaking is recommended for a backpack sprayer or use of an automatic agitation mechanism for larger equipment in order to keep the material suspended in water. Efficacy is only successfully achieved with thorough coverage. Care should be taken to cover the entire surface of the crop. Hydraulic sprayers at full dilution apply a better covering than mist blowers using concentrated sprays.
Re-entry interval and Pre-harvest re-entry interval (PHI): 4 hour REI. May be applied up to the day of harvest.
OMRI Listed products: Surround WP®, Engelhard Corporation
Concerns: The white film, while non-toxic, may reduce marketability if not removed (eg on edible fresh fruit, vegetables. It can be wiped or brushed and washed off after harvest. To avoid this, applications can be discontinued earlier to allow for natural weathering of the material. Care should be taken to protect workers from the dust generated during mixing and application.
Effect on the environment, human health | Soil effects are likely to be similar to natural kaolin clay in the soil. Since Surround® is applied at high concentrations, beneficial insects that come into contact with the direct spray would likely be affected, but less so once the material dries on the plant. Inhalation of dust can cause lung damage. Use a respirator when handling. Its LD50 is above 5000 mg/kg (Engelhard Corp 2003).
Types of pests it controls: Surround has been shown effective against several orchard pests, including apple maggot, white apple leafhopper, and pear psylla (Heacox 1999). It gen erally gives at least fair control of plum curculio and several species of fruit pest caterpillars (codling moth, oriental fruit moth, tufted apple bud moth, lesser appleworm). However, university trials also show that heavy use is harmful to beneficial species, and can lead to a flare up of European red mites or San Jose scale.
Surround has shown potential against pepper weevil, cabbage aphid, and onion thrips on vegetables in field trials, though more research is needed. It has been effective in the lab against flea beetles, but less so in the field.It has shown some repellancy against the silverleaf whitefly in the lab (Liang and Liu 2002). Surround has shown inconsistent results against the striped cucumber beetle in field trials; however, it was applied on a weekly basis in these trials. Some growers have reported better results against the cucumber beetle when Surround is used twice weekly when plants are small and more susceptible to damage from this pest. An experimental kaolin product has also given good control of grape and cucurbit powdery mildew and brown rot in peaches in controlled trials. This product is not currently available commercially.
ATTRA. 2004. Reduced-Risk Pest Control Factsheet: Kaolin Clay for management of Glassy-winged Sharpshooter in Grapes. http://attra.ncat.org/attra-pub/PDF/kaolin-clay-grapes.pdf
Engelhard Corporation. 2003. Surround“ WP and Surround at Home Crop Protectants Material Safety Data Sheet.
Engelhard Corporation. 2001. Surround® WP label.
Glenn, D. M., G. Puterka, T. Vanderzwet, T. Byers, and C. Feldhake 1999. Hydrophobic particle films: a new paradigm for the suppression of arthro-pod pests and plant diseases. J. Econ. Entomol. 92:751-771.