Understanding Pesticides
By Bob Chapman
"Pesticide" is an all-inclusive word used to designate anything that kills pests such as insects (insecticide), fungus (fungicide), mites (miticide), weeds (herbicide), slugs and snails (molluscicides), nematodes (nematicides) and bacteria (bactericides).
For centuries, ever since man moved from a nomadic existence to a hunter-gatherer then to an agrarian society, farmers and home vegetable gardeners bemoaned the fact that many insects devoured their crops, often leading to starvation and eventual death of loved ones because of the loss.
ORGANIC PESTICIDES
Over the centuries, since the raising of food became the chief means of survival, farmers have tried using many plants or their extracts to eradicate the insects and diseases that ravaged their crops. An organic (natural) pesticide is one that has components found in plants, animals or minerals, or whose action is a result of a biological process such as Bacillus thuringiensis, or commonly known as "Bt".
Be aware that an "organic" or "natural" pesticide does not mean harmless to humans if the concentrate or spray is inhaled, ingested, gets into the eyes, on the skin or used incorrectly.
Insecticides (not in any order of popularity or usage)
Horticultural oils. Horticultural oil (highly refined petroleum product such as Volck Oil), mineral oil, garlic oil, citrus oil and Neem oil (containing azadirachtin, from the seeds of the neem tree of India and Africa) are widely used by organic gardeners. Oils suffocate the insect and must contact and cover the insect to be effective. Some fungicidal effects are also claimed with the use of some oils.
Insecticidal soap (not a true soap, but the potassium salts of fatty acids found in animal fats and plant oils). Some use homemade detergent mixtures. Soaps, either commercial products or homemade, enter the breathing tubes of insects, causing their collapse and the death of the insect.
Sabadilla. Made from the seeds of Schoenocaulon officinale of Venezuela, containing alkaloids. It is used as dust. Moderately toxic to honeybees, mammals and causes violent allergic reactions in susceptible individuals. It is effective on a wide range of insect larva and adults.
Boric acid. Very effective when combined with a food that attracts ants and cockroaches. Commercially made traps are available or you can make your own.
Ryania. From the shrub Ryania speciosa and sold as a dust. It is touted as a broad-spectrum insecticide. Often found in mixtures of ryania, pyrethrin and rotenone.
Rotenone. Extracted from a variety of plants and once very popular, but because of new products available and rotenone's deadly poisonous nature, is now seldom used.
Pyrethrins or Pyrethrum. The Pyrethrum daisies (Chrysanthemum cinerarariifolium and C. coccinium) contain compounds that kill insects on contact. Pyrethrins are effective broad-spectrum insecticides and can safely be used in the garden, on vegetables and on fruit trees. These sprays and dusts are often mixed with sulfur or other compounds, giving them fungicidal properties or with other botanical insecticides. The products containing pyrethrins are commonly found.
Nicotine sulfate. Known for decades by gardeners and farmers as Black Leaf 40, this highly poisonous insecticide is extracted from a tobacco selected for its high nicotine content. Nicotine is highly toxic to mammals when taken internally or absorbed through the skin. You must wear protective clothing, including gloves, goggles and a respirator when spraying this insecticide.
Lime. An old-time insecticide. Wear protective gear, including gloves, goggles and a respirator when applying to prevent inhalation of the dust.
Ammonia. Household ammonia is used to control many insects, but refrain from use in hotter weather. Ammonia may injure the leaves of some plants so test before usage.
Quassia. From the wood and bark of the Quassia amara or Bitterwood tree. Typically, the bark and wood chips are spread over the soil or are ground up to make sprays.
Alcohol. The sprays containing 70% isopropyl alcohol (rubbing alcohol) are used outdoors and indoors on waxy-foliaged houseplants, controlling many sucking insects.
Attractants: These natural products, usually sex pheromones, are the chemical signals used by insects to attract mates. Attractants are used to trap insects and as mating disruption lures (they emit vast amounts of odors, making it difficult for the males to find the females).
Bacillus thuringiensis (commonly called "Bt"). Probably the most widely used (there are over 35 varieties of this bacteria) biological control. After Bt is sprayed on the plant caterpillar pests (includes cabbage loopers, codling moth larvae, imported cabbage worms, spruce budworms, diamondback moths, gypsy moth larvae, tomato hornworms and others) ingest it as they feed. It does not kill the insect or larva immediately, but the insect stops feeding. It may live for several more days, but soon darkens, dies and drops to the ground.
ORGANIC FUNGICIDES
Mildews, scabs, rots and rusts disfigure many flowers, shrubs, shade trees and fruit trees. Farmers and gardeners have used some of these fungicides for many years, long before any inorganic fungicides were developed. As with insecticides, exercise caution when using, following directions explicitly as stated on the label.
Sulfur. One of the longest in use, sulfur is used to control both insects and as a fungicide. It is considered a protectant fungicide. It is sold as a dust (containing a small amount of clay or talc to enhance dusting qualities) and as a wettable powder (it has a wetting agent added). Do not use sulfur when the temperatures exceed 80 degrees F. Use only plastic sprayers, as sulfur corrodes metals. Use protective gear when dusting or spraying.
Lime-sulfur. When lime is added to sulfur the fungicidal qualities of sulfur is enhanced. Lime lets the sulfur penetrate the tissues, becoming an eradicant, killing recently germinated fungal spores. The addition has a downside, the possibility of plant damage. Test the spray (or dust) on a small section of the plant. Do not use when the temperatures exceed 85 degrees F. When using, wear protective gear, including gloves and goggles.
Bordeaux mix. This old-time fungicide is a mix of copper sulfate and hydrated lime. Used as a spray or in wettable powder form and has insecticidal and insect repellent properties. Bordeaux mix controls many plant diseases, such as mildews, rusts, leaf curl, fire blight and some bacterial diseases. Read and follow label directions carefully, refraining from use when temperatures are below 50 degrees F. and testing for possible foliar damage.
Baking soda. Used as an eradicant, killing organisms that infect a plant as well as being a protectorant. Its qualities are enhanced with the use of horticultural oil in equal amounts and mixed with water.
Copper. Has been used since the invention of the printing press as pesticide, exhibiting fungicidal as well as herbicidal properties. Copper inactivates enzyme systems in fungi, algae and plants. Copper is toxic to humans and other mammals so use protective gear when using.
Compost tea. A solution concocted from finished, manure-based compost does double duty, feeding the plants and serving as a fungicide. The tea is said to outcompete the troublesome fungi, such as powdery mildew and botrytis blight, thereby inhibiting their growth.
Organic nematicides
Chitin. Found in seashells, chitin causes an increase in the growth of soil beneficials. These, in turn, produce an enzyme that destroys nematode eggs and larvae. Adding organic fertilizer with a nitrogen content is needed to help feed the beneficials, as the decomposition of the seashells uses up the available nitrogen. Chitin can be used on all ornamentals, fruits, nuts, vegetables and lawns.
INORGANIC PESTICIDES
Scientists, recognizing the desperate need to overcome the damage that insect pests and diseases caused farmers and gardeners developed pesticides that would eradicate or limit the insects and diseases that damaged or ruined their crops.
An inorganic (synthetic) pesticide is one whose components is manufactured and do not normally appear or occur in nature These wonderful, powerful chemicals, developed over the past decades to combat many pests in the garden, do a fantastic job in controlling them.
NOTE: Caution must be taken when using or spraying these pesticides. Always follow directions and take any precautions noted on the label. Many of these pesticides can cause harm when the concentrate or spray contacts the skin, gets in the eyes, is inhaled or accidentally ingested.
Insecticides. These products kill a wide range of insects, either by contact or by ingestion by the target insect. The more commonly found insecticides are acephate (Orthenex), carbaryl (Sevin), Malathion, Imidicloprid (Merit or Tree and Shrub Insect Control) or pyrethroids (synthetic versions of plant-based pyrethrins, includes cyfluthrin and permethrin).
Miticides. Mites are not true insects, as they have eight legs, no antennae or true jaws. Almost microscopic in size, they cause a lot of damage. Among the well-known mites are the red spider mites, russet (or rust) and the citrus bud mite. Sprays containing ethion, an organic phosphate, are commonly used to control mites.
Herbicides. These chemicals kill weeds and plants by disrupting a phase in their growth. Some are selective, killing only a certain type of weed (broad-leaved, grasses) while others will kill anything that the spray contacts. Glyphosate (Roundup, etc.), glufosinate-ammonium (Finale), sethoxydim (Grass Getter), 2,4-D/2,4-DP (Brush Buster) and triclopyr (Brush Killer) are currently on the market.
Fungicides. Rusts and powdery mildews on roses and many, many other popular plants cause discoloration and deformation (curling) of the leaves. In some cases a fungal infection can cause the complete loss of leaves (defoliation). There are hundreds of known fungi that attack plants, either above ground or through the roots of susceptible plants (for example, oak root fungus). Tribasic copper sulfate (Micro-Cop and Liqui-Cop) are widely used fungicides.
Molluscicides. Snail baits can be in a granular, pellet or liquid form. They usually contain metaldehyde, a chemical that dehydrates slugs and snails when eaten.
Bactericides. Bacteria cause gummosis in fruit and nut trees. These microscopic animals can also attack many flowers, shrubs and trees in the landscape and in houseplants. Tribasic copper sulfate (Micro-Cop) helps control many outbreaks but some bacterial infections resist control.
Nematicides. Nematodes are microscopic worms that live in the soil, feeding on plant roots, damaging or stunting them. A few species feed on plant stems and leaves. Severe infestations can lead to the death of a plant due to the inability of the plant to supply insufficient amounts of moisture and nutrients. There are no products on the market for homeowner use in controlling nematodes. Soil sterilization is sometimes used to control nematodes.
USING PESTICIDES WISELY
-Insects and diseases may develop a resistance to many pesticides, both organic and inorganic. Gardeners may find it necessary to switch to different pesticides if insect or fungal populations do not seem to be affected or lowered by the poisons used.
-Carefully read the directions and precautions twice before using pesticides. Use all protective gear recommended on the label.
-Use all pesticides sparingly and wisely. When inorganic pesticides first came on the market, gardeners would spray the landscape "fence to fence" unaware of the consequences of their actions. Spray only the target insect or fungus or plant.
-Some pesticides are toxic to birds, bees, fish and some mammals. The label will tell you if it is. If using homemade pesticides, be aware of potential harm.
-Sadly, insecticides do not distinguish between the "good guys" and the "bad guys" and all too often we eradicate the beneficial or harmless insects when using an insecticide.