DIATOMACEOUS EARTH: those rare deposits of one -celled diatom.

By J. Mullin
from Acres U.S.A. (a Magazine for Eco-Agriculture)

A thriving, healthy ecological farm and garden is the best argument against the ominous threat that 50 million will starve if we quit using toxic chemicals. When crops are threatened with severe damage, eco-growers look beyond the utopian claims of poison sprays and seek safer methods. One of the most effective materials for controlling insects may be diatomaceous earth.


Approximately 300 million years ago, countless trillions of minute one celled plants called diatoms existed in the oceans. They constructed tiny shells about themselves out of the silica they extracted from waters. When the diatom died, its microscopic shell was deposited on the floor of those ancient seas. Through the centuries, these shells eventually collected into deposits, sometimes thousands of feet thick. When the waters receded, the deposits were eventually covered and the shells fossilized and compressed into a soft chalk-like rock called diatomaceous earth.

When diatomaceous earth is quarried, milled, finely ground, passed through a screen and put through a centrifuge, it becomes a fine talc-like powder. This powder can be safely handled with bare hands, fed to animals and used to kill insects on contact. The process of destroying insects with diatomite is entirely mechanical, unlike the action of chemical insecticides, Diatomaceous earth is a non-toxic, inert material containing useful minerals such as manganese, magnesium, iron, titanium, calcium, silicon, and so on. Proper milling cracks apart the diatom skeleton, exposing microscopic silica needles. Sharp and hazardous to the insect, these needles are harmless to humans and other warm-blooded animals. The tiny size and razor-like construction of a diatomite fragment is just right to disrupt the life process of insects. The size of warm-blooded animals - as well as physical differences - confines the destructive effects of diatomaceous earth to insects.  The reason is that the skeleton of warm-blooded animals is inside, surrounded and wrapped by the muscle, which it supports, and the entire organism is protected by hair, fur, or feathers. Insects, however, have their frame outside. Vital fluids are held in and protected by an oily or waxy seal over a hard porous cover. If an object is small and sharp enough, it will scratch the insect's waxy seal, allowing insect to dehydrate and die. Minute sharp particles are also taken internally by certain insects and interfere with their breathing, digestion and reproduction. The tough external tissues of animals make them immune to damage from these same microscopic needles.

Diatomite dust can be applied without requiring protective apparatus, and only prolonged breathing of volumes more than 20 million particles per cubic foot of air, eight hours a day, five days a week (such as found in grinding mills) required the protection of a filter mask.

The idea of using dust to eliminate undesirable insects is not new, nor was it first developed by man. Birds and mammals have been taking dust baths to rid themselves of insects for  millions of years. Nor is the idea of using diatomaceous earth as an insect control modern. The Chinese used diatomaceous earth and diatomite over 4,000 years ago. The principal was rediscovered by Francis S. Leise and Neil Clark in Arizona in recent times.

Diatomaceous earth can also be used to control worms and other internal parasites in animals when fed as 1 or 2 % of a total animals ration. The control is simple, gentle and natural. There is no check to the organism, and if fed on a regular basis internal parasites are prevented.

In 1966, R. P. Link head of the Department of Veterinary Medicine at the University of Illinois, reported his diatomite experience: "I can relate on experiences when it was incorporated as 2% ration fed to cattle. It had no apparent effect and there is no evidence that any of it is absorbed and no residues appeared in the milk."

One outstanding benefit of feeding animals diatomaceous earth is that these animals seems to produce manure with a certain degree of built-in fly control and with reduced odors.

Insects in the field are repelled by diatomite dust applied to row crops and orchards. Bees will tend to avoid contact with blossoms treated with diatomite. Chewing and sucking insects will contact the particles more frequently than beneficial predatory insects as their bodies much be closer to the surface of plants where diatomaceous earth has been applied. Gardeners and farmers using diatomaceous dust say that it will destroy predatory insects, however, with proper application timing (late evening or night). Predator destruction is held to minimum.


As a mechanical insecticide, diatomite excels in protecting stored grains, seeds, legumes and possibly nuts. In an evaluation of four inert dusts compared to an insecticide efficiency of Malathion (a chemical compound), USDA research reported all four dusts were superior to the standard application of 1.0 pints of premium-grade 57% Malathion. In every test except one, the diatomaceous earth protected the wheat more effectively than Malathion.

Arrowhead Mills of Hereford, Texas has used diatomaceous earth for grains storage since 1966 and the storage has been most satisfactory. Hayden Mills in Phoenix, Arizona pioneered the use of diatomaceous earth in large-scale mills. Their main elevator holds more than three-quarters of a million dollars worth of wheat, and according to mill Superintendent Lawrence Manly, ³We don't worry about bugs anymore because we just don't have any.

Probably the largest company to experiment with the use of Diatomaceous earth in their storage and packaging is Northrup and King Company, who specifies the use of the Perma-Guard brand of Diatomaceous earth on and in seed packages, Northrup and King Company arranged and conducted a number of research projects, privately and through D. A. Miller, Glenn Sawyer and Ann Docahy of the Kansas Agricultural Experimental Station. One such project was to determine the effectiveness of diatomite in preventing damage to sunflower and by the Indianmeal moth. Diatomite was reported to be a significant improvement over other controls. In addition, rodent hairs, insect fragments and feces matter in grains, cereal, dried fruits, etc., was reported to range from very little to none, repeated studies consistently reveal than when grains have been stored with diatomaceous earth, the insect fragment could well below the count from grains stored and treated with chemical fumigants. Diatomite is more effective in preventing insects from entering grains in the first place.


There are quality differences in types of diatomaceous earth. Possibly the basic difference is between marine and fresh water supply deposits. Fresh water diatomites are low in silica and apparently; some deposits contain diatomite that is not effective against bean weevils. Exactly what properties are important has not been determined.

Farmers and gardeners who use diatomite as an insect control give conflicting reports ranging from modest to superb results. Users have claimed that diatomaceous earth is deadly to gypsy moth, coddling moth, pink boll weevil, lygus bug, twig borer, thrip, mites, earwigs, cockroaches, slugs, mosquitoes, and on and on.

Dr. John J. Grebe, for 40 years the Director of  Research, basic and unclear, for the Dow Chemical Company, believed diatomaceous earth offers a major opportunity for broad-spectrum control of insects without risk or pollution. In his judgment, a positive crash program should be initiated to develop effective techniques for controlling specific insects within the specific climates. For example, he pointed out that in hot, humid weather, the outside moisture balances the internal moisture lost by scratched insects and therefore they continue to survive. He also stressed the difference of various diatomaceous earths, and the skill of the individual farmer in using a mechanical contact insect control.


Fred Bracken of Palisades, Colorado, uses diatomaceous earth to control a mixture of insects on 319 acres of apple, peach, apricot and cherry orchards. Among these harmful insects are aphids, brown mite, twig borer, orient fruit moth and coddling moth. His insect control program consists of entirely conscientious applications of diatomite at night, and averages about $25 an acre per year.

While Bracken is enthusiastic about the effectiveness of diatomite as an insect repellent, he is pessimistic about the average farmer's willingness to follow such a conscientious program: 95% of your farmers today don't know about the life cycle of insects. They want someone to tell them when to spray... you've got to get out there and know what's going on. Using diatomite, Bracken's insect damage last year was about 2% from twig borer on the first pick and 2% from orient fruit fly. By dusting a day or two before harvest, there was no brown rot.
Diatomaceous earth works about as well as the farmer works. Early and conscientious applications will control a wide variety of destructive insects. Precisely what insects, how and how effectively requires more investigation and someone to do the right kind of research.