Kaolin clay is an organic pesticide often sprayed on trees, vines, and vegetables to prevent many insects and diseases, such as aphids, mites, leafhoppers, leaf rollers, thrips, apple maggots, cucumber beetles, and powdery mildew. The clay provides a protective layer on the leaves and fruits that irritates these pests and prevents them from reaching the leaf tissue. It is often used as an organic alternative to conventional pesticides.
Even though kaolin clay has a good track record when used on many crops, there are exceptions to the rule. USDA researchers in Texas sprayed kaolin clay particle film on cotton plants to control aphids. The results were the exact opposite of what was expected. Aphid populations actually increased after kaolin clay applications.
Researchers suggested the aphids might have been attracted to the lower temperatures associated with the kaolin-coated cotton leaves when compared to the untreated leaves. This research illustrates the need to test any spray for possible side effects before widespread use.
For more information on this kaolin clay research, go to: Entomologia Experimentalis et Applicata .