Reducing Heat Stress and Insect Pressure in Crops Using Kaolin Clay (Surround WP) - Part 1

Based on the extreme heat and drought that most farmers experienced not only in Missouri but in many areas of the Midwest, in this article I discuss the advantages of using kaolin clay (one trade mark is Surround WP, an OMRI-approved product that has both sticking and spreading agents incorporated) to protect plants against excessive heat and sun radiation while reducing insect pressure.

What is kaolin clay? Kaolin is a naturally occurring clay resulting from weathering of aluminous minerals such as feldspar with kaolinite as its principal constituent. Kaolin is a common mineral, considered “generally regarded as safe” by the U.S. Food and Drug Administration. It is 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. 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 does it work? This material has several modes of activity. According to the manufacturer, the principal use of Surround WP is to reduce heat stress; thus, the use of Surround WP can increase overall fruit yields in regions with high light and temperature levels because Surround’s specially engineered kaolin particles reflect harmful infrared and ultraviolet radiation. With less radiation and cooler fruit there is less sunburn damage. However, kaolin also 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.

Formulation and application guidelines: Kaolin clay is available as a wettable powder (i.e., Surround WP) 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. 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.

Reentry interval (REI) and pre-harvest interval (PHI): 4 hour REI. May be applied up to the day of harvest.

Tomorrow you will read case studies of kaolin clay with different crops.
(by Jaime Pinero, State IPM Specialist, Lincoln University)