Learn about how to control pests in garden using chemicals!
A bewildering number of apparently different pest-control chemicals confronts the gardener in his selection of a suitable material for the job he has in mind. Frequently the salesmen themselves are baffled by the number of new commercial names appearing on materials and can give but little advice on the proper selection. Unfortunately, chemicals vary greatly in their power to destroy the various types of insects and diseases.
The choice of the most suitable one for the pest is fully as important for success as the correct timing of the application and the proper manipulation of the equipment. Don’t let the glib salesman or the package with the most attractive label sway you in your choice.
How to Select Sprays or Dusts?
There are two considerations in the selection of materials to control plant pests, no matter what trade name glares at you.
First, make your selection on the basis of the active ingredient in the container that will do the job. There are surprisingly few of these basic active ingredients. Most packages name the active ingredient or ingredients and the amount contained. It is not advisable to buy blindly when this information is lacking. The active ingredient required will be determined by the pest or pests to be controlled.
Second, other things being equal, make your selection on the basis of cost. This may be very misleading unless you understand that price comparisons should be computed on the basis of a unit of diluted spray or dust applied, and not on the basis of a unit of concentrated material purchased in the store. For example, one material may be priced at $4.00 per gallon, and advertised to control the same pests as another material selling at $8.00 per gallon.
But if the directions on the first material state that it must be diluted 1 part to 200 parts of water, 100 gallons of actual spray will cost $2.00; while the second material, if effective at 1 part to 800 parts of water, will cost only $1.00 per 100 gallons of diluted spray. Thus, according to the directions of dilution, the $8.00 per gallon material is twice as cheap as the $4.00 per gallon material. Unless specifically directed otherwise, all directions furnished with materials should be carefully followed, as it is required that pest- control materials do as claimed when directions are followed.
The Basic Pest-Control Chemicals:
There are comparatively few basic pest-control materials with which the average gardener need concern himself. He should acquaint himself with the uses of each of these so that alternate materials may be selected if a shortage develops.
1. The Stomach Poisons:
Poisons that take effect when swallowed by insects while feeding are referred to as stomach poisons. Some are used on foliage and fruits; others are mixed with materials attractive as a food to certain pests in the form of poison baits.
Lead arsenate, usually purchased in powder form, is the most widely used chemical to control chewing pests on foliage and fruits. It can be used both in sprays and in dusts with safety to all but the tenderest foliage. Its main disadvantage is that it is poisonous to humans and animals, and so should not be applied on plants when there is danger that poisonous residues will remain on them at harvest time. When used on fruits, applications should cease about two months before harvesting; on vegetables, shortly after pods, fruits, or heads are half grown.
Calcium arsenate is often used as a substitute for lead arsenate, as its use eliminates the danger of a poisonous lead residue. It is more likely to injure foliage than lead arsenate, but it has the advantage of being more poisonous to insects. The addition of hydrated lime, equal in amount to either of the arsenicals, reduces the danger of injury to foliage.
Cryolite, mined naturally or made synthetically in the form of a powder, has recently gained wide use as a substitute or replacement for the arsenicals in the control of certain chewing-insect pests on vegetables and fruits. It is relatively non-injurious to foliage, and it is claimed not to be as dangerous a poison to animals and humans as the arsenicals. It is sold to be used in sprays or diluted with talc or sulfur and ready to use as a dust. The same precautions given for the arsenicals to avoid poisonous residue should be taken with cryolite.
Rotenone, which also goes under the name of derris powder, cube root, or timbo, is the safest stomach poison to be used on ripening fruits and vegetables, as it is harmless to warm-blooded animals. It may be purchased, if available, as a liquid extract or a powder containing 4 to 5% rotenone for use in sprays, or as a 0.5% dust ready to use. Its chief drawback as a stomach poison or repellent is that it loses its poisonous nature gradually in about one week after being applied.
2. The Poisons in Poison Baits:
The materials effective in poison baits are usually too injurious to foliage to be used in sprays or dusts. Most of them are also highly poisonous to men and animals, and therefore must be used with extreme caution. The baits are generally placed under and near plants so that the pests can find them easily. Most poison baits may be purchased ready for use under various commercial names; some can be prepared at home as needed. The poison baits effective against such insects as grasshoppers, crickets, cutworms and certain weevils usually contain either white arsenic, Paris green, or sodium fluosilicate.
A poison bait may be prepared at home as follows:
Thoroughly mix the above ingredients dry and add a mixture of the following slowly while stirring –
The juice and ground rind of a lemon or orange may be added for increased attractiveness. The mixture should be moist enough to form lumps when squeezed.
Poison baits containing thallium sulfate are most effective against ants; and those containing methaldehyde are most effective against slugs or snails. Red squill mixed with foods on which rats are accustomed to feed makes an effective rat poison. It is relatively nonpoisonous to humans or animals that can regurgitate—rats can’t.
Zinc phosphide, a highly poisonous grayish powder sold under the name of “Field Mouse Rodenticide,” is very effective against field mice when dusted on foods attractive to them. Because of its highly poisonous nature, it is obtainable only through county agricultural agents and a few authorized dealers.
3. The Dormant Contact Killers:
Poisons that take effect when they come in contact with an insect’s body are referred to as contact insecticides. They may be divided into those used in the dormant season on plants and those used during the summertime.
The miscible oils and lubricating-oil emulsions, when diluted with water according to directions, are effective against red-mite eggs and to a lesser degree against scale insects on fruit trees in the dormant season, but they do not destroy aphid eggs. The lubricating-oil emulsions are usually more effective, but are also more likely to cause injury. Both types of oils are sold under numerous trade names.
The “di-nitro” compounds are yellow dye like materials that have recently gained prominence because of their effectiveness against aphid eggs, most scale insects, and disease-producing spore centers in the dormant season. They are not, however, effective against red-mite eggs. They may be obtained in two forms: as dry powders or as a thin paste, Elgetol, to be diluted with water. They stain woolen materials permanently, but readily wash out of cotton goods. Elgetol washes off painted surfaces, so it may be used near houses or fences. To make an all-round dormant spray on apple trees, 4 teaspoonfuls of Elgetol may be added to each gallon of diluted oil-emulsion spray.
Liquid lime-sulfur is used in the dormant season at a strength of 1 part to 9 parts of water for the control of the San Jose scale and peach leaf curl, a fungus disease. It is caustic to the skin and permanently discolors painted surfaces. It is not recommended for use near houses or painted fences.
4. The Summer Contact Killers:
The summer contact sprays and dusts are sold under hundreds of different trade names, yet they all contain only one or more basic active ingredients, such as nicotine, pyrethrins, rotenone, thiocyanates, or refined mineral oils.
Nicotine for contact insecticides is sold as a solution of nicotine sulfate containing 40% nicotine. It is effective against a number of soft-bodied sucking insects, especially aphids. It is poisonous to humans, but no poisonous residue remains on the plants treated after two days. Soap or other wetting agents should be used with it for maximum effectiveness. Nicotine may be also purchased in the form of tobacco dust containing about 1% nicotine; or diluted with hydrated lime at strengths of from 1 to 4% nicotine.
Pyrethrum is obtained from the ground flower heads of a daisy like plant. It is not poisonous to warm-blooded animals, but has a rather rapid paralyzing effect on contact with the bodies of many insects. It is sold in the form of dusts ready to use, or as liquid concentrates which must be diluted with water. In dust form it is very effective in vegetable gardens against many chewing as well as piercing- sucking insects. Pyrethrum, like rotenone, loses its killing power rapidly on exposure to air and light, and therefore it must be kept in tightly closed containers when it is not in use.
Rotenone, a stomach poison, is better known for its contact effect on insects. It is usually slower than pyrethrum in its lethal action against insects. Because it also tends to deter insects from feeding on treated plants, it makes an excellent general garden spray or dust.
The thiocyanates, “Loro” and “Lethane,” are synthetic contact poisons in liquid form. They are relatively non- poisonous to humans and animals, and they are effective against many of the same insects as nicotine.
The summer oils are usually highly refined, white mineral oils that form milky solutions when diluted with water. They are obtainable under several trade names. They are used mainly on fruit trees for red-mite control, or in combination with other materials to increase their effectiveness.
5. Disease Killers:
The materials used to prevent or destroy plant diseases (fungicides) also appear under many trade names. Their chief function is to form a protective layer on foliage and fruit so that germinating disease spores will be killed before they can enter the plant tissue. Some have the added ability to “burn out” certain diseases already established. In most cases a disease once established cannot be eradicated, but may, with some conscientious spraying or dusting, be prevented from further spread.
The two most important groups of materials used on plants for disease control are the copper compounds and the sulfur compounds. The copper compounds are used mainly in vegetable gardens and on small fruits, while the sulfur compounds are chiefly used on fruit trees, where they also help control red mites. Neither type of compound leaves poisonous residues.
Bordeaux mixture, a chemical combination of copper sulfate and hydrated lime, is the oldest and still most useful disease preventative and eradicator for use on plants. It may be purchased as a dry powder to be diluted with water, or it may be prepared fresh at home, in which case it appears to be more effective. Homemade Bordeaux mixture is prepared in small quantities, as follows –
Dissolve 7 ½ tablespoonfuls of monohydrated copper sulfate (bluestone) in 2 gallons of water. Add to that slowly, while stirring, a lime solution made a half-hour previously, by mixing 10 ½ tablespoonfuls of fresh hydrated lime in 1 gallon of water. This produces 3 gallons of a sky-blue mixture (Bordeaux mixture) ready for use. It must be applied immediately after preparation; otherwise & teaspoonful of dissolved sugar should be added to preserve it for a few hours.
Copper-lime dust, usually containing 80% hydrated lime and 20% monohydrated copper sulfate, is used as a dust substitute for Bordeaux spray. It must be applied when the foliage is wet, so that a Bordeaux film is formed on the foliage.
The “low-soluble copper” materials, such as yellow copper oxide, are similar in action to Bordeaux, and may be purchased under trade names for use in sprays or diluted and ready to use as dusts. They are widely used on vegetable crops, as they do not have die stunting effect that Bordeaux may have on some crops.
Lime-sulfur solution is a heavy caustic liquid rather disagreeable to use but widely used on fruit trees in the summer, both to prevent and eradicate a number of diseases. It will “burn out” apple scab spots on apple foliage and prevent its spread. It discolors painted surfaces permanently.
Wettable sulfurs of the finely divided micronized types are as effective as lime-sulfur solution in preventing diseases and are safer on foliage. They are not disagreeable to use or injurious to painted surfaces. They are usually sold in powder form to be diluted with water according to directions.
Dusting sulfurs are very finely divided sulfur particles used in dust form as a substitute for sulfur sprays. They are usually not as effective as sulfur sprays, but are quicker and easier to apply. The foliage should be damp for best results. Unlike lime-sulfur, the wettable sulfurs and dusting sulfurs are not effective in destroying diseases already established.
Fermate is a promising new synthetic disease preventative which looks like finely ground charcoal. At present it has been used very successfully in spray form for fruit-tree diseases and may supplant the sulfur compounds for that purpose. Thiosan is another new promising fungicide.
How to Increase the Effectiveness of Sprays and Dusts?
It is possible to increase greatly the effectiveness of some sprays and dusts by incorporating with them other materials which make the spray or dust stick to, spread on, or wet the waxy coatings of leaves, fruits, or insects. Stomach poisons, disease preventatives, and dusts are best helped by stickers which prevent too rapid weathering and to some extent by spreaders which help make more even deposits. Contact poisons can be made more effective by the additions of spreaders and wetters which increase their penetration into insects’ bodies.
Some common examples of stickers and spreaders are fish-oil soaps, soybean flour, skim- milk powder, and wheat flour. Many products which increase the effectiveness of sprays are obtainable under various trade names. Many contact sprays and fungicides already contain spreaders and wetters and do not need additional ones. Read the directions on containers carefully.
Sulfur sprays and dusts have been found to be more effective fungicides if a small amount of lime is used with them; and rotenone diluted with pyrophyllite as a dust was found to have higher killing power than when diluted with talc or clay. Powders in spray solutions should always be made into a thin paste with a small quantity of water before they are added to the main solution. Spreaders and wetters should usually be added to the water in the sprayer before any other ingredients.
Helpful Combinations of Pest-Control Materials:
When two or three types of pests can be controlled at the same time, it saves considerable time and effort to combine insecticides or insecticides and fungicides.
Safe and compatible combinations for the control of chewing insects, piercing-sucking insects, and diseases may be made as follows:
1. Lime-sulfur or wettable sulfur, plus nicotine sulfate, plus lead arsenate.
2. Bordeaux mixture, plus nicotine sulfate, plus lead arsenate.
3. Bordeaux mixture, plus summer oil emulsion, plus lead arsenate.
4. “Low-soluble coppers,” plus nicotine sulfate, plus lead arsenate.
5. “Low-soluble coppers,” plus rotenone or pyrethrum.
6. Wettable sulfurs, plus rotenone or pyrethrum.
7. Fermate, plus summer oil emulsion, plus rotenone.
8. Fermate, plus summer oil emulsion, plus lead arsenate.
The powder forms of the above chemicals may also be mixed in similar combinations and diluted with talc to form all-purpose dusts. Many spray and dust combinations similar to the above may be purchased under various trade names. If they are made up at home, a good sticker and spreader should be incorporated with the spray unless oil is used in the combination.
How Much Spray or Dust Material Will You Need?
Many an enthusiastic gardener, determined to keep all pests away from his garden, has ended up by purchasing much more material than he could ever use in a single year. Fresh materials are usually more effective, so it does not pay to overstock on pest-control chemicals. In the case of fruits, with the aid of the spray schedule, you can figure out the approximate number of gallons of each spray needed to protect your trees fully, and from that figure you can determine the amounts of each active ingredient in these sprays that you will need.
Amount of Spray per Application on Trees:
Dormant sprays require about one half as much spray per tree as summer sprays with hand-operated equipment. One hundred pounds of dust give about the same thorough tree coverage as 650 gallons of spray; or, when dusting, 1 pound of dust will equal about 6.5 gallons of spray in tree coverage.
In the case of vegetables, the amount needed is more difficult to determine, as the frequency of the applications will be based on weather conditions, die type and age of the crop, and the abundance of certain pests. For small gardens, under 1,000 square feet, 5 pounds of a stomach-poison dust, 5 pounds of a contact dust, and 5 pounds of a fungicide dust should be more than ample under ordinary conditions. If spraying materials are used, about ½ pound of a stomach poison, ½ pound of a fungicide, and ½ pint of a contact poison should be enough.
Always look at die diluting directions, for they will help determine how much you will need. In gardens where the plants are small and spaced, about 2 quarts of diluted spray or 2 ounces of dust are required for 50 feet of row for each application. Don’t wait for pests to appear before purchasing materials; be prepared to prevent them from showing up whenever possible.
Calculating and Measuring Dosages:
For convenience and ease in measuring the correct dosages in the preparation of sprays and dusts, every gardener should be equipped with the following implements:
1. A set of standard measuring spoons, consisting of ½ teaspoon, ½ teaspoon, 1 teaspoon, and 1 tablespoon.
2. A measuring cup marked in quarters, a quart measure marked in quarters, and a gallon measure.
3. A 12-quart wooden or metal bucket with a stirring paddle for mixing spray or dust materials.
Useful Figures in Calculating Dosages:
Liquid Measure:
3 level tsp. = 1 level tbsp.
2 level tbsp. = 1 oz.
16 level tbsp. = 1 cup
2 cups = 1 pt.
16 oz. = 1 pt.
2 pt. = 1 qt.
4 qt. = 1 gal.
Liquid Dilutions (Approximate):
1 ½ tsp. in 1 gal. = 1 to 800 dilution
2 ½ tsp. in 1 gal. = 1 to 400 dilution
4 tsp. in 1 gal. = 1 to 200 dilution (0.5%)
2 ½ tbsp. in 1 gal. = 1 to 100 (1%)
5 tbsp. in 1 gal. = 1 to 50 (2%)
7 ½ tbsp. in 1 gal. = 1 to 33 (3%)
10 tbsp. in 1 gal. = 1 to 25 (4%)
12 ½ tbsp.in 1 gal. = 1 to 20 (5%)
Dry Measure:
3 level tsp. = 1 level tbsp.
16 level tbsp. = 1 cup
2 level cups = 1 pt.
28.35 g. = 1 oz.
16 oz. = 1 lb.
453.6 g. = 1 lb.
Approximate Dry Measures Useful in Making Up Sprays:
Rotenone Dusts:
To make a 0.5% rotenone dust from a powder containing 4% rotenone, mix 1 part by weight of the rotenone powder with 7 parts by weight of diluting material such as talc or pyrophyllite; to make a 0.5% rotenone dust from a 5% rotenone powder, mix 1 part by weight of the rotenone powder with 9 parts by weight of a diluting material.
How to Store Pest-Control Chemicals?
Many insecticides and fungicides are purchased in paper bags, but if they are to be kept for any length of time they should be transferred into metal or fiber containers with tight covers. Label the materials properly and keep them in a cool dry place where children or animals cannot meddle with/them.
When the season’s spraying and dusting are completed, all leftover sprays and dusts should be carefully saved and protected for the next year. Dusts must be stored in dry locations. Basements or other rooms that have some heat are best, since there is less chance of condensation of moisture in the air and consequent caking or deterioration of the materials. Rotenone and pyrethrum dusts are best stored in tight containers just large enough to accommodate them.
Liquid spray materials should be stored where they will not freeze. Extreme temperatures may cause the products to deteriorate or freeze and break the containers.