Farmers working in their orchards and vegetable fields may get irritated on hot, dusty days when a fine film of dirt adheres to them, distracting them from their chores. It turns out that the effects of a fine layer of minerals similarly irritate insects, and horticulturists have exploited this in the development of an organic barrier pesticide, kaolin clay.
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Kaolin clay is a common, natural mineral derived from feldspar. The U.S. Food and Drug Administration consider this mineral so safe that food and cosmetics manufacturers even add it to their products to prevent them from caking. In its agricultural application, processors grind the mineral to a fine powder and suspend it in water to help it cling to plants. Agricultural kaolin clay is commonly marketed as Surround.
Kaolin clay interferes with insects on several levels, giving organic farmers a high level of efficacy with minimal toxicity. Although kaolin clay applications produce a fine film on crops, it’s enough of a barrier to prevent insect pests from accessing tender foliage and fruit. The vivid reds, purples, and greens of host plants that act as a beacon to insect pests is camouflaged by the white residue of kaolin clay, which confuses insects. Finally, the product distracts insects when the film sticks to the pests, interrupting their feeding and normal behavior.
Kaolin clay affects many orchard insect pests, including apple maggots, the coddling moth, and the dreaded plum curculio. The utility of kaolin clay isn’t limited to the fruit orchard, as this product controls several vegetable pests including cucumber beetles, flea beetles, onion thrips, pepper weevils, and the cabbage aphid.
Organic farmers must combine kaolin clay with water according to package directions. As kaolin clay has superior caking properties that are valued in applications other than farming, the product should be agitated frequently during application to avoid clumping. This may involve using a mechanical agitator in large operations, or can be as simple as shaking a backpack sprayer for a small field treatment. Adequate coverage of the crop is necessary for the kaolin clay to have the maximum impact against insects.
The same features that make kaolin clay an effective insect control can also diminish the value of the crop: fruits and vegetables with a white filmy coating are unappealing to consumers. Farmers can cease applications a few weeks before harvest to allow rain to wash the clay away, and they can wipe off any lingering residue.
Although kaolin clay is nontoxic, the product can damage the lungs if a farmer inhales it during application. Workers can prevent lung damage by using a respirator during application.
Source:
Cornell University College of Agricultural and Life Sciences
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