Does Diatomaceous Earth Kill Potato Beetles?

What is Diatomaceous Earth?

• Diatomaceous earth is made from the fossilized remains of diatoms, a type of single-celled plant. DE is mainly composed of silica and is sharp, but the particles are so small that they do not affect humans or pets. They are lethal to insects and their larvae, however, and are an effective method of controlling garden pests, such as the Colorado potato beetle. DE can be purchased at home and garden centers or online. It is considered a safe food additive by the EPA.

Colorado Potato Beetles

• Colorado potato beetles can do serious damage to a crop of spuds, and they are infamous for developing resistance to pesticides. Adult bugs are about 1/2-inch long, with orange heads and striped black and yellow bodies. They spend the winter in the soil and emerge in the spring to feed and lay their eggs. Potato beetle eggs look like clusters of yellow dots on the underside of the potato leaves. The larvae of potato beetles are red with black spots, and this is the stage when DE is most effective against them.

Using DE to Kill Potato Beetles

• DE kills potato beetles and other pests by cutting their skin, in the case of larvae, or the exoskeleton of adult insects. Simply sprinkle the powder on the soil around the potato plants, or dust the undersides of the leaves. You can use a puffer to apply the dust, or you can fill a glass jar with DE, place a piece of flexible window screen over the top of the jar and secure it with a rubber band. Be sure to label the jar. DE loses much of its effectiveness when it gets wet, so you will need to reapply it after rain. Bees and other beneficial insects are also susceptible to DE, so apply it before the potato flowers bloom and cover the plants with a light-weight, floating row cover or an old sheet to protect the bees and ensure the potato beetles come in contact with the DE. When the flowers begin to bloom, remove the covering and rinse the DE off the plants, unless rain has washed them for you.

Food Grade DE

• The type of DE used in gardens is called "food grade," but there is another form used in filtration systems for swimming pools. Make sure you get the food grade DE for killing potato beetles, because the pool variety is not effective for pest control. It has been washed and heated and will not cut the insects.