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Kaolin

© Deborah Turton

I’m going to start this column by stating that I don’t grow fruit, and I haven’t used Kaolin. Therefore, none of this information is from personal experience. However, Kaolin is a new product that may be useful to fruit growers, and I felt it would be a good idea to discuss this product.

Kaolin is a clay that is edible and has been used in a variety of food products. The EPA considers it ‘generally recognized as safe.’ Not surprising since the public has been eating it for a while.

Kaolin is combined with water and sprayed on fruit trees to act as an insecticide and fungicide in some cases. The most common brand name is Surroundä.

Kaolin works by creating an inhospitable environment for insects on the trees or vines. The clay coats the tree and irritates the insects in the same way that sitting on a towel covered with sand irritates you at the beach. The insect leaves to find a more hospitable location. When using Kaolin, it is very important to cover all of the surfaces. If not, the insects will find the clean areas on your trees. They will simply feed and reproduce in these areas. Kaolin has been found to be effective on pyslla, apple leafhoppers, thrips, apple rust mites, codling moths, leafroller moths, and mealy bugs. Because kaolin affects all insects it can reduce the number of beneficial predators. Therefore, it can also reduce parasitism of leafminers, and their numbers might increase with use. Obviously, if your major problem is leafminers, Kaolin should not be your first choice.

Kaolin has also been found to be beneficial during times of heat stress. It coats the tree with a white film that reflects the sun. You’d think that this would lower photosynthesis, because the leaves are coated and the sun is being reflected. However, the opposite happens. With a lower leaf temperature, the stomata (holes) that allow carbon dioxide to enter can stay open longer in the afternoon. (Stomata close when the leaf becomes too hot.) Researchers have found that kaolin coated trees can have a 30% increase in photosynthesis. Their apples and pears are larger without a decrease in the number produced. Sunburn damage on fruits and nuts is reduced when sprayed with Kaolin.

Some people have been experimenting with raising the pH of the kaolin spray. This controls powdery mildew and apple scab. The more alkaline spray apparently made the tree less hospitable to these microorganisms.

The copyright of the article Kaolin in Organic Gardening is owned by Deborah Turton. Permission to republish Kaolin in print or online must be granted by the author in writing.