MACDONALD J. 47( 2): 14, 42 (May, 1986)

by Professor Stuart B. Hill

Department of Entomology and

Ecological Agriculture Projects

For centuries stored grain has been protected from insect attack in much of the less developed world by adding some form of powder or dust to it. Common materials include plant ash. lime. dolomite. certain types of soil, and diatomaceous earth (DE) or Kieselguhr.

With me introduction of synthetic pesticides in the 1940s, and modern fumigants some time later, it was felt that a scientific solution to pest problems had been found. Although tnese materials provided enormous local benefits. a number of problems are beginning to be recognized. These include the development of resistance by insects. pollution of the environment. contamination of foodstuffs with residues, and exposure of users to toxic chemicals. This has led a small group of researchers and developers .to look again at the different powders to see which are most effective and how they can be improved.

Probably the most effective naturally occurring protective powder is diatomaceous earth. This is a geological deposit made up of the fossilized skeletons and tests of siliceous marine and fresh water organisms, particularly diatoms and other algae. These skeletons are made of hydrated amorphous silica or opal. When crushed, they break up into tiny pieces of glass'' (so tiny that the material feels like talcum powder). This is easily picked up by the hairy bodies of most Insects. whereupon it scratches through their protective wax layers; and they also absorb some of this material. the result being that the insects lose water rapidly . dry up and die Further protection is provided by the powder's property of repelling many insects. A similar principle probably accounts for the fact that birds frequently take dust baths, presumably to rid themselves of parasites.

Although patents for diatomaceous earth formulations were issued in the United States in the late 1800s it was not until the 1950s that the first commercial formulations of it became widely available, and between 1963 and 1970 a series of studies on DE were conducted by the U.S. Department of Agriculture.

In several tests, DE gave better protection of grain than malathion, particularly over the long term, without exposing anyone to the dangers of toxic chemicals. At that time relatively large amounts of DE were added to grain to provide protection, e.g., 3-1/2 kg/tonne. The main problem with using this amount was that it tended to make the grain very dusty and it reduced its flow rate and test weight.

Today this problem has been greatly reduced through the use of improved DE formulations that contain baits and attractants. Such formulations have been developed and tested in Quebec through the collaborative work of Mr. Arthur Carle (P.l.P. Products Inc., 2721 Plamondon, Longueuil, Que., J4L lSl) and myself. Using NCr, one of these formulations, as little as 0.5 kg/tonne may provide full protection. Despite this, very little grain in Canada is treated with these DE formulations. One of the main reasons for this is that present regulations prevent the adding of any powder to grain destined for export. Until such rules are changed the full potential of DE will not be realized. This is especially frustrating in the case of grain going to developing countries as aid. While this grain may be pest-free when it leaves Canada, it is often rapidly invaded by insects when it reaches its Third World destination. It is not uncommon for 20 per cent of this grain to be subsequently lost! to pests. If DE had been added prior to export, however, it would have been protected indefinitely. Fortunately, DE can be added to domestic grain as long as it doesn't pass through licensed elevators. It can also be used in grain and food handling and storage areas such as flour mills, empty grain bins, box cars, ships' holds, warehouses, food processing plants, etc.

In houses it can be used effectively to prevent the entry of certain insects such as earwigs, ants, and cockroaches, and to control these and others that are present in cupboards containing food, carpets, basements, attics, window ledges, pet areas (for fleas), etc. In all of these examples it is important to place a small amount of the powder in corners, cracks, crevices. and other areas where insects might hide.

Whereas with a contact pesticide the insect dies quite quickly, with DE control may take several days. The more important difference is that the effect of the protection provided by the chemical is short-lived. whereas DE will control the pests as long as the powder remains. In this respect DE is an ideal pesticide; it is residual but nontoxic. The only health precautions that need to be taken are that if large areas are being treated with a power duster, the applicator should wear a mask to prevent inhalation. Because DE is made of silica, people sometimes mistakenly think that DE causes silicosis. As indicated above, however, pesticide quality DE is usually over 97 per cent amorphous silica, which does not cause silicosis, which is associated only with crystalline silica. Indeed, inhalation of road dust and grain dust IS likely to be more harmful than DE.

In the field DE has potential in certain restricted uses such as treating the bark of fruit trees in spring using an electrostatic duster, or the roots of plants when transplanting: but because it is non-selective and also kills beneficial insects, its use here should be carefully controlled.

Another use is in animal production units for the control of external parasites and flies. This is achieved by dusting the animals and the litter or bedding area. It has also been included in the diet (two per cent in the grain ration) to control certain internal parasites, and this practice is said to result in lower fly populations in the resulting manure.

In the future, improvements in the formulation of DE to reduce dustiness and more effectively lure insects to it to ensure their rapid exposure will no doubt extend its use. In the meantime, it is perhaps the safest effective pesticide for use in the home and has a valuable place in the protection of stored food and control of insects in animal production units.

DE may be purchased in Quebec from Chemfree Environment. Inc. (514-630-4400), and from garden centres.

Copyright 1986 Ecological Agriculture Projects







Diatomaceous Earth: The "Silver Bullet"


by Howard Garrett


Not long ago, I started talking about diatomaceous earth as an insecticide. Boy, was I a genius. This stuff had only been around since near the beginning of time. It's been nature's insecticide since than and its other uses are many. So why haven't the university systems and all the gardening experts been recommending it for years?

More recently I started talking about using natural DE as a food supplement for animals. The results are almost too good to believe - even for me, and the question again comes up - why am I the only one recommending this stuff? Seems like the vets should be extolling the virtues of DE from the highest hills.

Undaunted ( hard headed might be a better choice of words), I wrote about DE in the Dallas Morning News and when I started the gardening show at WBAP, it was the main topic of conversation. So much so that my boss told me that show was getting a little boring from talking about DE every call. I didn't ask the questions - just answered them.

Natural diatomaceous earth (DE for short) is the remains of microscopic one-celled plants (phytoplankton) called diatoms that lived in the oceans that once covered the western part of the United States and other parts of the world. Huge deposits were left behind when the water receded. They are now mined and have several important uses in toothpaste, beer filtering, and swimming pool filters. DE is approximately 3% magnesium, 86% silicon, 5% sodium, 2% iron and many other trace minerals such as titanium, boron, manganese, copper and zirconium.

Natural DE also makes a very effective natural insecticide. The insecticidal quality of DE is due to the razor sharp edges of the diatom remains. When DE comes contact with the insects, the sharp edges lacerate the bugs' waxy exoskeleton and then the powdery DE absorbs the body fluids causing death from dehydration. Said more simply, DE kills insects by drying then up. You'll see how drying DE is if you handle it with bare hands.

There is no residual danger of contamination. In fact, DE is actually beneficial to the soil. It's loaded with trace minerals. However, there are a few precautions. Diatomaceous earth is very dusty and can cause lung problems if breathed heavily, so when applying it dry always wear a good dust mask or stand up wind. The second precaution is that DE sold for swimming pool filters is ineffective for insect control because it has been heated and chemically treated. It won't kill insects and it is very dangerous to breathe. Finally natural DE will kill beneficial insects too, so use it sparingly to kill problem infestations of harmful insects and don't use it too often.

Diatomaceous earth can be applied in a variety of ways. to use for flea and tick control, apply a light dusting over the lawn, in dog runs, around pet bedding or favorite resting spots and sprinkle a little on your pet between baths of a mild herbal soap. Avoid Dips and soaps containing chemical insecticides. It's also a good idea to avoid soaps that contain ammonium laurel sulfate. It's used to make good studs but it is a skin irritant. Check out your own soap and tooth paste while you're at it.

The best way to apply the dust over a large area is with a light weight apparatus such as Dustin' Mizer, Spritzer or other similar blowers. Applying by hands can be done but wastes a lot of material and will dry your skin. To apply with water, mix 1/4 cup of DE in a gallon of water and apply to the lawn and/or shrubs where pest problems exist. It doesn't hurt insects until it dries out.

One of the best uses of DE is to add it to animal food - pets or livestock. When used at 1% to 2% of the food volume, it controls internal parasites, increases digestion and provides valuable trace minerals. You will usually see an overall increase in health of any animals fed DE on a regular basis.

Here are some of the common questions I get on natural diatomaceous earth.

Is DE dangerous to my pets, me or my family?

Since DE is dusty and abrasive, it can cause lung damage if breathed heavily. remember, however, that breathing any dusty materials can be dangerous. be sure to wear a dusk mask if applying with a dry blower. Mixing into a water spray eliminates most of these problems. DE will not hurt earthworms or beneficial soil microorganisms. DE is one of the few pesticides in the world classified as non-toxic, although I'm not real comfortable with the classification. I think anything can be toxic if over used or misused.

How much DE should I feed my animals?

Some of the feeding rations suggested by suppliers and users include: 1-2% by weight of DE in ground, dry feed. 5% by weight in stored grain. 5 ounces ( one cup) daily ration for horses. one tablespoon per day for large dogs (over 55 lb.). One teaspoon per day for small dogs, cats and puppies.

Does spraying DE in a wet solution work as well as the dry dust?

The wet spray method does work but only after the liquid had dried. Mix from 1-4 tablespoons DE per gallon of water and spray on the lawn, shrubs, tree trunks and building foundations. When the mixture dried, it has the same abrasive and dehydrating powers as the original dry dust. When sprayed wet the material covers the foliage and other surfaces better than dusting dry, thus giving better insect control. It seems to last longer when applied wet, but the dry application is usually more effective at killing insects quickly. DE has no insect killing power while it is wet.

Can I mix DE with other sprays?

Yes, it can be mixed with other organic products such as seaweed, fish emulsion, garlic tea, and biostimulants. it would be silly to mix DE with chemical insecticides. In fact, it's silly to use synthetic toxic pesticides for anything.

Is DE registered by the EPA and labeled for insect control?

Yes! Some people would have you believe that DE is untested, unlabeled and therefore unsafe for use. That's just one of the feeble arguments left to the organiphobes. DE has been used for years in the food processing industry to treat stored gains to eliminate weevil and other insect infestations. There are currently dozen of registrations of DE with the EPA for various insecticidal and food supplement uses. DE, with and without pyrethrins and piperonyl butoxide, is registered and labeled for fleas, ants, roaches and many other pests.

Piperony butoxide (PBO) is a synthetic synergism that is added to increase the killing power of the product. I do not recommend it for any use. Those wanting to avoid it can mix pure pyrethrum and DE together at a 25% -75% ratio. Pyrethrum products that are available include Natural Guard and ECOsafe . There is approximately 1% pyrethrin in natural pyrethrum powder. Pyrethroids are synthetic insecticides. They do not resemble natural pyrethrum and should not be used.

(note: ECOsafe was a tradename for Natural Animal)


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