By John M. Chater
Kaolin clay is used as a crop protectant in many crops, including tree crops like citrus. This clay is often white to grayish white and is commonly used to reduce sunburn on fruit and young trees. Kaolin also has been demonstrated to reduce pest feeding and activity in some tree crops.
The albedo from the clay reflects and refracts light to reduce radiation on leaves. The geological characteristics of the clay make pest activity, including movement and feeding, more difficult for some pest species. Despite the clay covering the leaves, the plants are still able to conduct photosynthesis and transpire water to cool off. The clay easily washes off of the fruit in the packinghouse.
There are multiple products on the market that have kaolin clay as the active ingredient. Some are more expensive than others. Some of these products have been certified by the Organic Materials Review Institute to be used in certified organic systems.
The use of kaolin clay in citrus-producing regions, including Florida, has a long history. With the summer heat and the high level of solar radiation on Florida farms, kaolin is a good option to reduce the harm caused by abiotic stress factors.
One important consideration for using kaolin clay in Florida is the incidence of rain. Because a lot of sunburn occurs during the summer months, one would expect to utilize this product then. But the frequency of rainfall in the summer months can wash off the kaolin clay, which causes its efficacy to be reduced substantially.
In California, kaolin is used in citrus and other crops, such as avocado and pomegranate. It rains much less in the summer in California, so the applications stay on. It is typical to apply kaolin clay in several passes. It has been observed that trees can look as if they have been snowed upon when the product is applied multiple times, for instance, on pomegranates.
In Florida, it would likely take more applications to get the coverage required to reduce sunburn. And as rains occur, more applications are required. It is unlikely that the desired effect will be seen with one application during the rainy season in Florida. As the citrus tree flushes, the new tissue will grow out of the kaolin, so more applications will also be needed in that case as well.
John M. Chater is an assistant professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.
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