Bilgiler > Natural Insecticids and Fungicides
Natural Insecticids and Fungicides
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Methods of Insect Control
Only organic means of insect control will be presented in this chapter. These methods include use of sprays and dusts, introduction of biological control measures, and
application of cultural practices. Insecticidal sprays and dusts are materials that killinsects or limit the activity of insects through chemical toxicity or physical action on
the organisms. Sprays and dusts may differ little from one another except in modeof application with one being applied in a liquid form and the other in a dry form.
Biological control involves the introduction of predators, parasites, or diseases thatfeed on or infest insects. Cultural practices include management procedures that
growers can employ to limit the access of insects to crops.
Application of Organic Sprays and Dusts
These pesticides are chemicals derived from mineral deposits, from plants, from animals, or sometimes by manufacturing from natural ingredients. Whether organically derived, all sprays and dusts should be handled with care, as they may present hazards to health. Usually some characteristic, such as abrasive or toxic action, is the factor that allows
prays or dusts to be insecticidal. Organic sprays and dusts can be as injurious to humans and other animals as chemically manufactured pesticides.
Often, the distinction between organic and nonorganic (“chemical, manufactured”) pesticides is marginal or weakly defined. Both types of insecticides should be treated the same. Directions provided with the materials should be followed, and records of application should be kept. The pesticides should be used only on the crops specified, in amount specified, and at time specified in the directions. The pesticides should be applied at the most susceptible stage of the insect.
In applications of insecticides, plants should be sprayed or dusted thoroughly, being sure that the pests come directly in contact with the pesticide or its vapors. Pesticides
should be applied in calm weather to lessen blowing and drifting. Application is recommended to be in the cool of the morning or evening. This practice helps to avoid injury to plants and to maintain the efficacy of the materials, protecting against their inactivation by heat, light, or drying.
The applicator should prepare only as much spray as is needed for treating of the crops. Excess material should be diluted with water and dumped away from all water sources. Pesticides, containers in which pesticides were held, and spraying and dusting equipment should be kept away from children, pets, livestock, poultry, and wildlife.
The applicator should avoid inhaling or swallowing the pesticide and should avoid contact of the materials with the skin. Proper equipment should be used to apply the esticides. Protective clothing, goggles, or masks may be needed. Care should be taken to avoid consumption of the pesticides on products that have been treated with sprays or dusts. Pick produce before the pesticides are applied, wait the appropriate time before harvesting treated produce, and wash treated produce if possible before consumption. These rules apply to purchased or to homemade pesticides.
Many of the materials described here as sprays also can be applied as dusts if the initial material is dry. Sometimes the insecticide for spraying is sold in a more concentrated
formulation than the dust. Growers should check with certifying agencies to determine the usage of these products in organic agriculture.
Sprays (See Table 11.1)
Water
Water alone can be an insecticide. Wetting of insects may cripple them or limit their movement on or onto plants. Wetting of hairy insects is facilitated by adding a few drops of soap solution or detergent. If water does not have an insecticidal action from these disabling injuries, it can help to lessen damage to plants by knocking the insects off plants. Insects can be washed off house plants and down a drain. Insects may be washed from bark or nests of insects by streams of water directed onto the plants. These effects of water are strongest against nonflying insects, such as aphids, cabbage worms, and red spiders.
Insecticidal Soaps
Soaps or detergents lessen the surface tension of water, allowing water to spread smoothly over the surface of leaves or insects and thereby improving the effectiveness of water as an insecticide. Soaps and detergents also are insecticidal. Dishwashing
Sprays for Insect Control by Organic Means
Water Alcohol Sulfur
Insecticidal soaps Diatomaceous earth Milk
Ammonia Salt solutions Whitewash
Mineral oils Starch
Neem
detergents are insecticidal but also are phytotoxic. With most certifying organizations, only soaps are considered to be organic pesticides.
Care must be taken not to use more than a few drops of soap or dishwashing detergent per gallon of water, that is, no more than 20 drops (about 1 ml) as a starting point, The phytotoxicity of these materials should be evaluated on a portion of a plant before widespread applications are made. Soaps or detergent solutions may collect in whorls or other areas of plants and concentrate upon evaporation to toxic levels. Plants with thin cuticles are more sensitive than ones with thick cuticles. For example, garden beans, cucumbers, and peas are sensitive to soaps and detergents, tomatoes and potatoes are less sensitive than those crops, and waxy plants such as cabbage are very tolerant of these sprays. Either soap or detergent solutions may be used as herbicides if the concentrations of the material are high enough in solution.
Insecticidal soaps are available on the market. Generally, these soaps are made from naturally occurring fatty acids. Diluted insecticidal soaps have low phytotoxicity and low mammalian toxicity and can be used indoors or outdoors. No residues are left to have long-te rm environmental effects. Soaps can be applied to crops up to harvest of produce. Soaps, or detergents, are effective against most soft-bodied insects, including aphids, spider mites, caterpillars, leafhoppers, whiteflies, mealybugs, and lace bugs. Soaps are less effective on scales and beetles than on soft-bodied insects. Beneficial as well as harmful insects can be killed by soaps or detergents. The effectiveness of the soaps or detergents comes from their action on the cuticle and cell membranes of insects. Cells in contact with the soaps or detergents become leaky, resulting in dehydration and death of the insects.
Detergents are manufactured materials and are not considered to be organic substances.
In fact, addition of detergents to certain potting media as wetting agents prohibits the use of these media in organic agriculture. Hence, use of detergents as insecticides is not likely to receive organic certification.
Ammonia
Household ammonia, sudsy or not sudsy, is as an insecticide. Ammonia is toxic to insects and plants. The household ammonia should be diluted about 4 oz. in a gallon of water to be applied as a spray. This mixture should be tested on a few leaves of the affected plants before it is used on the whole plants.
Mineral Oils
Highly refined mineral oils are applied as emulsions in water and are an organically acceptable chemical control. Oils coat bodies of insects and suffocate them.
No insect is known to have resistance to oils. Oils kill eggs and are very effective against scales, which otherwise are difficult to attack with insecticides. However, oils may injure foliage. Dormant oil should be used on leafless shrubs or trees or on some conifers, because it may defoliate broadleaf trees or shrubs. Dormant oil is known also as Volck’s oil. Sometimes the oil is marketed mixed with sulfur.
The sulfur increases the effectiveness of the oil as an insecticide and also gives fungicidal properties to the mixture. Summer oil or white oil is more refined and lighter weight than dormant oil. Summer oil can be used on leafed-out trees and shrubs but should be evaluated to ensure that phytotoxicity is not imparted by the spray.
Alcohol
Rubbing alcohol is marketed as a 70% aqueous solution of isopropyl alcohol. Scale insects can be wiped from plants with a cloth or cotton ball wetted with the undiluted alcohol. Insects such as mealy bugs can be daubed with undiluted alcohol with cotton applicators on a stick. Alcohol sprays can be prepared from 8 to 16 fluid ounces diluted into a quart of water, a dilution of one part alcohol to two to four parts water by volume. In either of the cases of using undiluted alcohol wipes or daubs or diluted alcohol sprays, precautions should be taken not to injure foliage. A small area or a few leaves should be tested with the alcohol before the whole plant is treated.
Alcohol is used against pests such as aphids, scales, and whiteflies.
Diatomaceous Earth
Diatomaceous earth is silica derived from fossilized marine algae called diatoms.
These algae are single-celled organisms that have an outer shell of silica.
Diatomaceous earth has many industrial and home applications, with common uses being in polishes and swimming pool filters. As an insecticide, it is a nonselective, abrasive material with particular effectiveness against crawling, soft-bodied adult insects, caterpillars, snails, and slugs. The particles of silica are microscopic and needlelike. The particles penetrate and abrade the waxy coating (cuticle) of insects, causing them to dehydrate. Diatomaceous earth is considered nontoxic to mammals, but if it is inhaled, it can be very hazardous by irritating the mucous membranes. Dust masks should be worn while it is being handled. The material can be dusted around the base of plants to control root maggots and soil-dwelling insects. It can be dusted on leaves to control chewing insects. Dew or irrigation water on the foliage helps to retain the diatomaceous earth on the plants. It can be applied as a spray in water instead of as a dust. A few drops of soap or detergent will improve the wetting action of the spray.
Salt Solutions
Table salt (sodium chloride) dissolved in water can be an insecticide that is effective against soft-bodied pests, such as cabbage worms, aphids, and spider mites. The insecticidal action of salt sprays is through their desiccating of the insects. Dissolve about 1 oz. of salt in a gallon of water to prepare a spray. This amount of salt in solution should not injure plants, but young plants may need to be tested on a few leaves before the whole plant is sprayed.
Starch
Starch sprays work by gumming up the leaves and trapping insects in place or by gumming up the insects if they are sprayed directly. Baking flour or potato starch dextrin can be prepared with a few tablespoons (2 to 4) per gallon of water or can be applied as dusts.
Sulfur
Sulfur is a naturally occurring mineral. It has insecticidal and fungicidal properties.
Finely ground sulfur is wettable and can be sprayed. Commercial products are available readily. Sulfur can be applied as a dust as well as sprayed. Sulfur might be applied in closed environments by vaporizing the sulfur from a heating element, but the safety and efficacy of this practice are questionable. Dusts may have clay or talc added to improve the dusting properties of the material. These specially prepared sulfur dusts would not be useful as wettable powders. Sulfur is a nonselective insecticide but is particularly effective against mites. Sulfur is also moderately toxic to mammals, fish, and other animals. Masks and protective clothing should be worn when applying sulfur to plants. Avoid use of sulfur in hot weather, because crop damage may occur. Sulfur is corrosive to equipment due to its oxidization and reaction with water and oxygen to form sulfuric acid.
Milk
Milk has insecticidal properties due to its proteins (globulins). Any kind of milk can be used. It is effective against soft-bodied insects such as cabbage worms. Milk also has some effects against fungi and viruses.
Whitewash
Whitewash is slaked lime (calcium hydroxide) prepared as a slurry in water. It is applied as paint on trunks of trees to protect against boring insects. Generally, whitewash should not be applied to foliage, unless it is prepared as a dilute spray that does not leave a heavy residue. Whitewash is fungicidal and offers protection against plant diseases when it is applied to plants. Storage rooms and root cellars often are whitewashed to control diseases that develop on stored produce.
Nicotine
Nicotine is an alkaloid from tobacco and is a powerful insecticide, one of the most toxic of the botanical insecticides. It is effective against most insects. It can be applied to soil or to foliage. A wetting agent (soap or detergent) in the spray helps with coverage of foliage. The fumes from nicotine are effective in control of insects, such as aphids, whiteflies, leafhoppers, and thrips that may be on the undersides of leaves or in the whorls of plants where liquid sprays may not reach. The volatility of nicotine allows it to dissipate quickly, although one recommendation with nicotine dusts is to use only on young plants to ensure no toxic residues at harvest. Nicotine sprays or dusts are or were sold as nicotine sulfate, which has a lesser mammalian toxicity than straight nicotine. Applicators should always check the label on the insecticide to ascertain permitted use of nicotine. Applicators should not remain in the area in which nicotine is applied especially in enclosed areas. Nicotine or nicotine sulfate, the insecticidal formulation, is highly toxic, and its use should be avoided by home gardeners.
It should not be used on pets or farm animals. Nicotine that is distilled to prepare sprays should have no tobacco mosaic virus, but again users should consult the label to determine effects on solanaceous crops, such as tomatoes, peppers, eggplants, and potatoes. Dusts prepared from stems and leaves of tobacco and nicotine teas are likely to have the mosaic virus. Nicotine teas are prepared from aqueous extracts of tobacco products, for example, a cup of cigarettes or cigars in a gallon of water.
The availability of nicotine formulations is limited in the United States to imported products. It is no longer registered commercially for insect control. Nicotine sulfate is prohibited for use in organic agriculture by the U.S. Department of Agriculture
(USDA) National Organic Program.
Neem
Neem or neem oil is extracted from seeds of the neem tree (Azadirachta indica), which is common in Africa and India. Neem is related to the chinaberry tree (Melia azadarach), which grows in the southern United States. Extracts of seeds of either species have insecticidal properties. The extracts have repelling, hormonal, and toxic effects against a broad spectrum of insects in larval or adult stages. Plants sprayed with neem extracts are unpalatable to insects. Neem is sold commercially. Neem has been reported to have fungicidal properties as well as insecticidal properties.
Neem has a low toxicity to mammals. It is offered commercially as an alternative to nicotine sulfate.
Limonene
Limonene is refined from citrus oils that are extracted from peels of oranges and other citrus fruits. It is generally regarded as safe by the U.S. Food and Drug Administration and is used widely as flavorings and scents in foods, cosmetics, perfumes, soaps, and degreasers. Limonene has low oral and skin toxicities to mammals and dissipates rapidly from surfaces, leaving no residual effects. Limonene is a contact poison to insects but may have fumigant activity. Limonene is used more commonly against external pests of pets to control fleas, lice, ticks, and mites.
Commercial products are available as sprays, aerosols, shampoos, aerosols, and dips.
Limonene has herbicidal activity. It affects the cuticle of plants and imparts desiccation.
Its use against insects on plants may be limited by this property. However, phytotoxicity of limonene is low.
Sprays Prepared from Plants
Many plants contain materials that are insecticidal and that can be extracted with water. Preparations are made by chopping leaves in a blender or by hand with soaking of the homogenate or chopped leaves overnight in water. Generally about 1 cup of fresh leaves is used per cup of water in which the leaves are blended or chopped and soaked. The blend is strained through cheesecloth or otherwise filtered to create the spray. The pulp can be discarded or used around plants as a possible insecticide.
Several garden plants contain compounds that are weakly insecticidal. Tomato leaves contain an alkaloid similar to nicotine. Onions, garlic, and turnip leaves have various sulfur-containing compounds, and rhubarb leaves contain oxalic acid. Other plants with chemical compounds that offer potential control of insects are hot pepper fruits, walnut or pignut leaves, and larkspur seeds. Most of the sprays prepared as described from this list of plants would be only mildly insecticidal. All of these plants have materials with potential harmful effects to mammals through direct toxicity, irritation of skin, or allergenic effects.
Dusts (See Table 11.2)
These plant-derived materials, or botanical insecticides, may be applied as sprays by their suspension in water as well as dusts. These insecticides are broad-spectrum materials, meaning that they have actions against beneficial insects as well as pests.
All of them have short-term residual activity on crops, but all of them have mammalian toxicity. Care should be taken when choosing botanical insecticides.
Pyrethrin
Pyrethrin, also called pyrethrins or pyrethrum, comes from one or more plants of the Chrysanthemum genus, called painted daisies, bug-killing daisies, or pyrethrum daisies. The botanical insecticide is available as powdered flowers of these plants or as an extract of the flowers and is referred to generally as pyrethrum.
Pyrethrum is the most commonly used of the botanical insecticides in the United States. Synthetic forms of pyrethrin are known as pyrethenoids and are ingredients in many of the popular house and garden sprays and in some sprays known as white-fly sprays. Natural pyrethrum only may stun insects and knock them to the ground. Insects often metabolize pyrethrum and recover. Synthetic forms in spray cans are fortified with a synergist, piperonyl butoxide, which also kills insects.
Pyrethrin is a broad-spectrum insecticide that poisons the nervous systems of insects and that has low mammalian toxicity. It is perhaps the least toxic of the botanical insecticides. Commercial preparations of natural pyrethrum are sold as liquid preparations often with rotenone or with insecticidal soaps. Pyola is a broadspectrum insecticidal spray prepared from pyrethrum and canola oil and is used against adults, larvae, and eggs of insects.
Homemade pyrethrum dusts can be made from powdered, dried, mature flowers of the painted daisy. Extracts can be made with by soaking a cup of packed flowers in 2 fluid ounces of rubbing (70% isopropyl) alcohol. The alcoholic extract can be diluted with water to make a spray. Pyrethrin seems to lose some effectiveness at temperatures above 80°F.
Rotenone
Rotenone is a plant product refined from roots of tropical Asian (Malaysian derris, Derris spp.) and South American (Peruvian cubé and Brazilian tembo, Lonchocarpus spp.) legumes. Rotenone is a broad-spectrum insecticide with high toxicity to chewing insects (e.g., various beetles) but provides lesser control of sucking insects (e.g., aphids) and of larvae and slugs. Rotenone is a respiratory poison interfering with the electron transport chain in mitochondria. It is quite toxic to mammals, birds, and
Table 11.2
Some Plant-Derived Dusts for
Insect Control
Pyrethrin Ryania Quassia
Rotenone Sabadilla
fish. Rotenone was used by American Indians as fish poison. It readily enters the bloodstream of fish through the gills, and the poisoned fish come to the surface and are caught easily. The fish could be eaten safely because rotenone is not absorbed readily in the gastrointestinal tract. Rotenone is used commonly today in fish management to eradicate unwanted or exotic fish from non-native bodies of water. Care should be taken not to use rotenone where it is likely to enter ponds and other bodies of water. Rotenone has residual effects on crops for about 1 week, so harvests should be scheduled for at least 1 week after rotenone applications. Commercial powdered preparations are 1% or 5% rotenone. The remainder of the mixtures is inert ingredients (carrier). Commercial mixes are sold as these dilute preparations because of the high toxicity of rotenone. The 1% preparations generally are used as dusts, whereas the 5% preparations may be used as dusts or as sprays. The preparations meant to be used as sprays should be wettable powders; otherwise, wetting of the powders meant for dusting is difficult. Rotenone has a shelf life of a year or less, and year-old materials are likely to be ineffective. Therefore, new materials should be purchased yearly, and growers should purchase only enough material for the current season to avoid waste and disposal of the material. Rotenone products, in addition to those marketed with it as the single active ingredient, may be sold as powdered mixes of rotenone,
ryania, and pyrethrin. Rotenone (1%) is also available as an emulsifiable concentrate with pyrethrin (0.8%) that can be mixed with water and sprayed. Rotenone is a very effective broad-spectrum insecticide, but because of its toxicity and because some evidence indicates that it causes growth abnormalities in test animals, growers may want to choose other organic insecticides that are safer to use. Rotenone is more toxic to mammals by inhalation than by ingestion. Applicators of rotenone should wear protective clothing and masks and follow all instructions written on the label for the material.
Rotenone has been used to control fleas, lice, mites, and insect larvae on livestock, pets, and poultry. Rotenone formerly was permitted in organic agriculture. It was removed from the list of approved substances of the USDA National Organic Program in about 2005 because of concerns about its safety. Except as a fish poison, its use is being phased out in the United States.
Ryania
Ryania is prepared from the stems and roots of a shrub (Ryania speciosa) from South America. It is a broad-spectrum, general-use insecticide with strong effectiveness against the larvae of various moths. It is recommended to control larval pests, such as corn borer, corn earworm (tomato fruitworm), cabbageworm, and codling moth, and for control of thrips, aphids, and several beetles. It has limited use against cabbage maggot, cauliflower worms, or boll weevil. Users should consult the label on the product to ascertain its permitted uses. Ryania is difficult to find in garden and farm stores but is available by mail order through garden supply catalogs. It is available as a single product or as a mixture with pyrethrum and rotenone. It can be applied as a spray or dust. Repeated applications at approximately 10- to 14-day intervals may be needed to provide season-long control of pests. Applications should be ceased
several weeks before harvest of produce. Ryania is effective in warm weather and has a shelf life of several years if kept cool and dry. Ryania is a much safer material than rotenone. Its mammalian toxicity is similar to that of pyrethrum. Users should wear protective clothing and masks.
Sabadilla
Sabadilla is made from the seeds of Schoenocaulon officinale, which is a lily-like plant native to Venezuela. The seeds contain poisonous alkaloids that are not in other tissues of the plant. Sabadilla is a broad-spectrum insecticide that offers protection against larvae and adults. Usage is most common as a dust, although the powder may be wetted and sprayed. Applications to plants should be about weekly to maintain control of pests. Moisture on the leaves helps the dust to stick to plants. Sabadilla degrades quickly in sunlight, moisture, and air so that it does not persist in the environment.
However, it has a long shelf life and seems to increase in potency with age in dark, dry storage. Sabadilla has low mammalian toxicity if ingested, but applicators should avoid inhaling the dust, as it can be irritating to mucous membranes. It is quite toxic to honeybees. Recommended times of use are in the evening after the bees have returned to their hives.
Quassia
Quassia comes from the bark and wood of a tropical American tree (Quassia amara) with bitter wood. This species is in the same family as tree of heaven (Ailanthus altissima), also with bitter wood. Wood shavings or bark chips of quassia are spread on soil at the base of plants to control insects. An extract of quassia may be made from ground wood or bark with hot water. The extract seems to be a weaker insecticide than the straight bark or wood. Quassia is sold as a medicinal herb and can be purchased in some natural food stores.
Lime-Sulfur
Lime-sulfur dusts can be made with mixed proportions of various limes (agricultural lime, quicklime, or hydrated lime) and sulfur. The ingredients also can be used individually. Quicklime or hydrated lime is a little more effective than agricultural lime alone or with sulfur because of their amorphous nature and reactivity.
The dry materials will not burn foliage. Growers will want to take caution against application of these materials to wet foliage. Hydrated lime mixed with water is whitewash, which can be used for insect control on trunks or stems of woody plants.
Science and Technology of Organic Farming_ Allen Barker
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