, Research Paper
Introduction
What is the goal of agriculture? Mainly, it is to produce healthy food, affordable for consumers to purchase, while ensuring that farmers are able to earn a decent income. Recently, with greater environmental awareness in society in general, it is also now very important to protect the agricultural environment. This is a big challenge for farmers as they must still obtain reasonable yields and produce quality produce in order to meet the demands of the market. Both these can be severely affected by harmful organisms, commonly referred to as pests (weeds, disease, etc.) that compete against, infect or damage the cultivated crop in a detrimental manner. The most economic and effective way to handle these has been to employ pesticides, many of which are now composed of synthetic chemicals, and it is these substances – very beneficial from the economic and production aspects of farming – which can pose risks to human health and the environment if not properly used.
Pest problems are not new; in fact, they have been around as long as agriculture itself. But the pest pressure faced by farmers is now as great as it ever was: the world’s fast-growing human population needs to be fed from an always shrinking base of agricultural land, and the substantial damage that can be inflicted by pests (e.g. insects, diseases, weeds, rodents, birds) on crops is the margin between a good harvest and a bad one. Pests can reduce the quality of a harvest as well as its quantity. Since the quality of food is increasingly important to consumers, a pest could reduce the value of a crop or make it unsaleable. But it is important to keep in mind that pests are not the only cause of yield
reduction and of lower quality produce: factors such as soil fertility and availability of water may have a greater influence in a particular situation.
Hence, crop protection has always been an important component of agriculture, leading to the development and employment of measures that can limit damage, such as synthetic chemicals. Easily stored for long periods in a compact form, easily applied at very short notice (provided the machinery is available and the weather conditions are suitable), they are fast-acting and efficient. They can also be toxic, and the farmer must use pesticides wisely to make sure that they will not harm the applicator, the farm family and the surrounding environment.
What Is Pesticide?
Pesticide
biological, physical, or chemical agent used to kill plants or animals considered harmful to human beings; see FUNGICIDE; HERBICIDE; INSECTICIDE.
? Fungicide
substance used to prevent or destroy a fungus. Made from sulfur or copper compounds, organic salts of iron, zinc, and mercury, or other chemicals, fungicides are used on seeds, soil, wood (to prevent dry rot), and fabrics (to prevent mildew). Human fungal infections are treated with fungicides, called antifungals or antimycotics in medicine, such as nystatin and clotrimazole.
? Herbicide
substance that kills plants or inhibits their growth. Nonselective herbicides, generally toxic, are used to clear all plants from a broad area; selective herbicides attack weeds without permanently harming crops. Scientists are using genetic engineering to develop crop varieties with increased tolerance for herbicides. Inorganic compounds such as common salts have long been used as herbicides; c.1900 certain sulfates, ammonium and potassium salts, and other compounds began to be used as selective herbicides. The 1940s saw the development of 2,4-D (2,4-trichlorophenoxyacetic acid), an organic compound that is a highly selective systemic herbicide. Such herbicides are now widely used. Several such compounds, including 2,4,5-T (2,4,5-trichlorophenoxyacetic acid), have been banned by the Environmental Protection Agency as potentially dangerous. 2,4,5-T was used in Agent Orange (a defoliant employed by U.S. forces in Vietnam), which has been linked to some diseases suffered by veterans. Since Agent Orange, heightened awareness of possible ecological and health dangers attributable to herbicides has resulted in reevaluation of many compounds and has called indiscriminate use into question.
? Insecticide
agent used to kill insect pests. Insecticides have helped increase the yield and improve the quality of crops, but there has been concern about the dangers of chemical insecticide residues in the ecosystem and in foodstuffs. Such concerns have led to governmental regulation and the replacement of some toxic insecticides that persist in
the environment (e.g., DDT and other chlorinated hydrocarbons) with compounds that break down more quickly into less toxic forms. The liabilities of chemical insecticides have encouraged interest in biological controls, which turn natural processes and mechanisms against pest insects and have few if any harmful side effects. Biological controls include using predators, parasites, and pathogens to kill target insects or using synthetic hormones to disrupt pests’ normal life processes. Increasingly, biological and chemical methods are coordinated in Integrated Pest Management programs.
Pesticides are unique among the hazardous chemicals. They are specifically designed and produced to kill or disrupt biological organisms. Ideally, pesticides should be highly selective, effecting only targeted organisms, but unfortunately most are not. Herbicides, for example paraquat, not only kill green plants, but may also be acutely toxic to human beings. Others cause cancer, birth defects, genetic damage and changes in human and animal endocrine systems.
Effects on Agriculture
1. Concerns About Pesticides
? Pest resistance
Pests, after repeated exposure to a pesticide, can start to build a resistance against the effects of the materials, especially chemicals.
In every population of or plant weeds, there is a very small population which is immune to the effects of the pesticide. As the affected population is eliminated by the pesticide treatment, the immune portion of the population slowly, year after year, becomes the dominant segment of the pest population. As a result, the farmer must apply more and more pesticide to achieve the same effect, risking greater damage to health and the environment. Eventually, the pesticide becomes ineffective and can lead to the collapse of some agricultural systems with highly resistant pests and no natural enemies left to control them.
Left: Irrigation ditch, a potential
highway for pesticides.
? Contamination and toxicity
Pesticides can be toxic to the surrounding environment – the plants, fish, animals, certain useful insects such as bees as well as to the natural enemies of the pests. The consequences to these latter species can be particularly dramatic since the devastation of a natural control agent population by pesticide use may result in a resurgence of pest populations.
The danger of toxicity to humans who handle or are closely exposed to pesticides is also important, and a great deal of care must be taken when using pesticides; this also applies to household applications of chemical weed and insect pesticides. Because of the interaction between air, soil and water, a pesticide applied to one medium (i.e. to the soil
in a field) can contaminate elsewhere as the material is transported to other locations once mixed with another medium (i.e. rain water that runs off into a river.) Pesticides spread further afield than where they were applied, and the consequences of unanticipated pesticide contamination can be as harmful as they are unexpected.
2. Case Study : Fate of Insecticides Used for Termite Control in Soil
Termites cause substantial damage to residential and commercial buildings in the United States. It has been estimated that the annual cost for controlling termites and repairing their damage in the United States exceeds $1.7 billion. Subterranean termites, the most destructive of all termites, account for 95 percent of this damage.
Because subterranean termites are soil-inhabiting social insects living in complex colonies, the conventional control method is to establish an insecticide barrier between the termite colony (usually in soil) and wood in a building. Currently, Pest Control Operators (PCOs) who specialize in termite treatments have access to more than 11 insecticides (termiticides) for subsoil application. However, due to differences in soil characteristics, and physical and chemical properties of termiticides, PCOs and the
general public often question how the soil and termiticide will interact. How long will the insecticide be effective in the soil? Is the degradation rate the same in different soils? Will the termiticide leach through the soil and contaminate nearby water sources?
It is important to examine some of the soil factors and chemical properties of termiticides that affect the behavior of these compounds to better understand these issues.
Major factors influencing efficacy and persistence of termiticides are:
Soil Characteristics :
? Soil Texture
Clay and organic matter contents are important characteristics influencing termiticide sorption mechanism. Clay and organic matter in soil can vary from less than 1 percent in sand to well over 50 percent in heavy clay soils. The vertical and horizontal distribution of termiticides is dependent upon the interaction with soil particles through processes called adsorption and desorption.
Adsorption is the binding of a termiticide to the surface of soil particles, especially clay and organic matter. Desorption is the release of adsorbed chemicals from a soil particle surface. Depending on many factors in a soil profile, such as moisture, pH, temperature, etc., compounds may adsorb and desorb from soil particle surfaces as they migrate down through the soil. It is also important to consider the clay, sand and silt content of soils because insecticides generally do not migrate as readily in soils with high clay and organic matter contents. The mineral content of soil is also an important factor in
determining the persistence of termiticides by either catalyzing decomposition or affecting the adsorption rate. Because groundwater contamination is an extremely important issue to PCOs and the general public, understanding how compounds bind to soil particles is an important part of evaluating whether a termiticide will leach. However, there are no conclusive research data to determine how adsorption/desorption affects termiticide efficacy and application rate in different soils. It is generally assumed that since termites come in contact with soil particles, it may not be necessary to adjust termiticide dilution rates for most soils. Additional research is needed to accurately determine if variable rates are needed.
? Soil pH
The soil pH is known to have a major impact on performance of termiticides because it affects how rapidly a compound degrades. The pH is used to describe whether soil is acidic (pH less than 7) or alkaline (pH above 7). Most soils have pH values between 4 and 8. In general, termiticides used today persist longer in acidic soil than in alkaline soil.
? Soil temperature and moisture
For the most part, termiticides will remain more efficacious and persistent in soils with low temperatures and low moisture content. Warm soil temperatures and moist conditions can enhance the activity of insecticide-degrading microorganisms, thereby increasing degradation of compounds.
? Soil Microorganisms
Microbial degradation is another process in which soil microbes utilize insecticides as substrate (food source) for growth and maintenance. However, little information is available on how microbial degradation of registered termiticides occurs in various soils.
Chemical Characteristics :
The second major element affecting termiticide performance involves the chemical characteristics of each insecticide.
? Solubility
Solubility of termiticides in water is an important factor affecting their distribution and mobility in soil, but it is not necessarily the best indicator of performance. For example, soluble compounds may have strong affinity to adsorb to soil particles, subsequently limiting their mobility through soil. Ultimately, a combination of factors determines the termiticide mobility in soil.
? Degradation
Termiticide efficacy and persistence are primarily affected by the degradation rate of that compound. Once the termiticides are applied to soils, their fate relies on degradation processes. As the termiticide degrades, it is transformed into other compounds that may be more or less toxic than the parent insecticide. Photodegradation: The breakdown of chemicals due to exposure to sunlight is not a major factor because termiticides are usually applied below the soil surface. Chemical degradation: The most important
process affecting termiticides is chemical degradation which involves hydrolysis, oxidation and reduction. This process directly affects the half life or residual of insecticides in soil.
Hydrolysis is a chemical process in which an insecticide reacts with water, resulting in splitting of the water molecules to form less toxic compounds. There is generally enough moisture in soil to initiate this reaction.
Oxidation is a chemical reaction through which an oxygen atom is added to the parent molecule of an insecticide. Initially, it may not appear that an oxidation reaction results in degradation of insecticides, but a more oxidized form of a molecule may be necessary for further microbial or chemical degradation.
Reduction is the third aspect of chemical degradation. An insecticide molecule is considered to be reduced if its hydrogen content increases or its oxygen content decreases. However, similar to oxidation, reduction may be a preliminary step toward further degradation by other processes. Reduction reactions generally occur under conditions where oxygen is limited (anaerobic environment). Reduction reactions may increase if a soil becomes flooded. As a result, termiticides applied to water-saturated soils may degrade rapidly, rendering the treatment unsuccessful. Areas with excessive water problems should always be corrected prior to termiticide application.
? Volatilization
This process involves transforming chemicals from solid or liquid into a gas or vapor. Several factors influence the tendency of termiticides to volatilize and leave soil as a vapor. The structure of the chemical is important because this determines its vapor
pressure as well as its solubility in soil water and its tendency to be adsorbed. Cool and dry conditions in soils with high organic matter or clay content normally result in very little loss of even the most volatile chemicals from the soil. Conversely, warm and moist conditions contribute to great desorption and greater volatilization losses.
Many processes influence efficacy, persistence and movement of termiticide in soil. Knowledge of these processes can ultimately lead to better understanding of behavior and performance of termiticide products in various soils.
3. 2,4-D RESEARCH DATA
2,4-D, a member of the phenoxy family of herbicides, was the first selective herbicide developed. It was introduced in 1947, and rapidly became the most widely used herbicide in the world.
A selective herbicide is one that controls weeds in a crop without damaging that crop.
After 50 years of use, 2,4-D is still the third most widely used herbicide in the United States and Canada, and the most widely used worldwide. Its major uses in agriculture are on wheat and small grains, sorghum, corn, rice, sugar cane, low-till soybeans, rangeland, and pasture. It is also used on rights-of-way, roadsides, non-crop areas, forestry, lawn and turf care, and on aquatic weeds. A recently published eight-year U.S Department of Agriculture study (NAPIAP Report NO. 1-PA-96) concluded that, should 2,4-D no longer be available, the cost to growers and other users, in terms of higher weed control expenses, and to consumers, in the form of higher food and fiber prices, would total $1,683 million annually in the U.S. alone. The study also reviewed the 2,4-D
epidemiology and toxicology data packages and concluded (page2) that after 50 years of extensive use, “The phenoxy herbicides are low in toxicity to humans and animals (1,9). No scientifically documented health risks, either acute or chronic, exist from the approved uses of the phenoxy herbicides.”
A study entitled. “An economic assessment of the benefits of 2,4-D in Canada” done in 1988 under Canadian Government sponsorship, Concluded that the net benefits of 2,4-D in Canada totaled a third of a billon dollars annually. A worldwide study of the benefits of 2,4-D measured in terms of increased food production and lower food prices has never been done, although those benifits are known to be enormous. 2,4-D has for the past fifty years, been a major tool in the continuing fight to reduce world hunger.
2,4-D is the most thoroughly researched herbicide in the world.
? 2,4-Dichlorophenoxyacetic Acid Toxicology and Environmental Toxicology
The 114 research studies completed in these areas under the EPA reregistration program confirm the existing toxicology data package. Apart from the hundreds of unpublished studies required by various regulatory agencies around the world, there are more than 4,000 peer-reviewed, published studies on 2,4-D in the scientific literature. The recent studies reconfirm:
? 2,4-D has moderate to low acute toxicity. The LD50 (rats) ranges from 699 mg per kg of body weight (2,4-D acid) to >1000 mg/kg for ester and amine
formulations. From an LD50 standpoint, 2,4-D is less toxic than caffeine and slightly more toxic than aspirin.
? At the concentrations which may be found in the environment, 2,4-D is highly unlikely to present a threat to wildlife.
? Subchronic effects are generally limited to very high doses when compared to the exposure levels humans may face in the environment.
? 2,4-D has low reproductive toxicity.
? 2,4-D does not cause birth defects.
? Chronic effects are also limited to high doses.
? Based on the extensive toxicology, it is highly improbable that 2,4-D causes cancer.
? 2,4-D has low potential to cause neurotoxicity in short and long term exposures.
? 2,4-D does not cause genetic damage.
Although the publications of many anti-pesticide advocacy groups continue to show 2,4-D to be a mutagen, there are no
? Environmental Fate
2,4-D has a relatively short half-life and is rather immobile in the soil. In 35 recent studies across the U.S., the average lowest depth detected ranged from 6 to 12 inches in soils of the southern United States to 16 to 24 inches in low organic soils. Soils were
sampled to a depth of 48 inches. Its average half-life in soils ranged from 6.4 days in southern soils to 8.3 days in high organic matter soils. The average half-life in grass was 6.1 days and 6.9 days in thatch. The half-life in natural water was two to four weeks, although in areas where soil microbes were conditioned to 2,4-D, such as a treated rice paddy, the half-life was as short as one day. The acid form of 2,4-D, as well as the amine and ester chemical groups, metabolized to compounds of nontoxicological significance and ultimately to forms of carbon. Thus, 2,4-D is considered a biodegradable compound. Under normal conditions, 2,4-D residues are not persistent in soil, water, or vegetation.
Prevention
Research and Development In Crop Protection
In crop protection, a lot of research is being done on products extracted from natural and biological sources as a result of people being more and more aware of environmental issues. Throughout the world, only 10 % of the plants have been studied on a chemical basis: there is then very likely a great potential that many plant chemical components could be used as bioherbicides, especially since living organisms do not develop
resistance as quickly and completely to natural products as compared with chemical products. But what is a bioherbicide? In simple terms, it is a preparation of a living inoculum of a plant pathogen, formulated, and applied in a similar manner to that of chemical herbicides in an effort to control or suppress the growth of weed species.
Examples of bioherbicides that have been registered for weed control are DEVINER, a liquid formulation of Phytophthora palmivora that was registered in 1981 for control of
stranglervine (Morrenia odorata) in Florida citrus groves and COLLEGOR, a dry powder formulation of Colletotrichum gloeosporioides f. sp. aeschynomene, that was registered in 1982 for the control of Northern Jointvetch (Aeschynomene virginica) in rice and soybeans in Arkansas, Louisiana and Mississippi. (Watson, 1989)
The use of bioherbicides will be more common in location and application situations where pesticide regulations are most restrictive. But bioherbicides also have limitations: they are less efficient in fighting against insects and pathogens compared to chemical pesticides, they are only effective 48 hours after their application (while it takes only a few seconds for non-biological products) and that the residual effect of the biological product does not last as long.
In Qu bec, products from plant sources used in crop protection are mainly:
? fertilizers made from algae
? biological insecticides made from plants
? 100 % natural insecticides made from fossilized sea algae (120,000 kg of powder bought annually) coming from California and Washington.
Alternative Pest Controls
Pest management and control includes more than the use of pesticides. Virginia agriculture already uses a number of non-chemical methods including resistant varieties, cultural controls, and biological controls. Growers are encouraged to implement these alternative controls whenever possible. Alternative controls are an integral part of any cropping system. However, where chemical controls are necessary, their use must be
managed in such a way as to provide for a safe food supply, a clean and healthy environment for humans and wildlife, and a productive and profitable agricultural industry.
Although this guide does not provide a comprehensive pest control plan for each crop or commodity, Virginia Tech encourages the use of alternative pest controls. For specific information beyond the scope of this guide, please contact your local Extension office or the authors of each specific section.
How to Get Help with a Pest or Pesticide Management Problem
The first rule in solving any problem is to properly identify the cause of the problem before you seek a solution. This rule especially holds for pest control. You MUST identify the pest before you make any attempt to control it. If you need assistance with pest identification, there is help available as close as your local Extension office. The telephone number of your local Extension agent is listed in the local government section of your telephone directory.
If a pest is especially difficult to identify or if confirmation is needed, as is often the case with plant disease problems, your agent will send a specimen to Blacksburg for identification. Services available at Virginia Tech include: The Plant Disease Diagnostic Clinic, the Insect Identification Laboratory, the Weed Identification Laboratory, the Soil Testing Laboratory, the Forage Testing Laboratory, and the Pesticide Residue Laboratory. All samples should be sent by your local Extension office. Many of these services may be used for solving pest control problems.
Safe and Effective Use of Pesticides on Agricultural Crops
Efficient and economical control of insects, plant diseases, and weeds is a factor in the production of all crops. Both the costs of control and losses resulting from inadequate control reach tremendous proportions each year. The use of today’s pesticides requires a great degree of precision. Only minute quantities of herbicides are needed to kill plants and many currently used pesticides are highly toxic to man and animals. In some instances, rates are given in ounces per acre. This requires that pesticide users know how to calibrate equipment and follow detailed directions outlined on chemical labels. PROCEED CAUTIOUSLY AND LIMIT THE ACREAGE TREATED UNTIL YOU HAVE GAINED FIRST-HAND EXPERIENCE IN THE USE OF PESTICIDES.
Warnings on the Safe and Proper Use of Pesticides
Pesticides vary in their toxicity to man and other animals, so all should be used with care. The following suggestions will help minimize the likelihood of injury (from exposure to such chemicals) to man, animals, and non-target plants and animals.
Read the Label – Before buying and applying pesticides always read all label directions and follow them – exactly. Notice warnings and cautions before opening the container. Repeat the process every time, no matter how often you use a pesticide. The label directions for pesticides often change from year to year. Apply materials only on crops specified, in amounts suggested, and at times indicated on the latest manufacturer’s label.
Store Pesticides Wisely – A suitable storage site for pesticides:
? protects people and animals from accidental exposure;
? protects the environment from accidental contamination;
? prevents damage to stored products (from temperature extremes and excess moisture);
? protects the pesticides from theft, vandalism and unauthorized use.
All pesticides should be stored under lock and key, outside the home. Storage facilities should be well-ventilated and well-lit. Pesticide storage areas should be located away from water sources such as ponds or wells. However, a supply of clean water for decontamination is recommended. Non-porous materials are recommended for flooring and shelving. It is important to locate materials in the storage site so cross-contamination does not occur. Do not store pesticides with food, feed, seed or fertilizer. An emergency
plan should be worked out with local authorities, notifying them of the contents of such storage facilities. If substantial quantities of highly toxic pesticides are being stored you must notify (according to law) your local Emergency Response Council. Proper recordkeeping should be maintained to provide for an up-to-date list of contents at all times. Always store pesticides in their original containers and keep them tightly closed. Never keep pesticides in unmarked containers.
Avoid Physical Contact with Pesticides – Never smoke, eat, chew tobacco, or use snuff while handling or applying pesticides. Protect your eyes from pesticides at all times. Avoid inhaling sprays or dusts. When directed on the label, wear protective clothing and a proper mask. Do not spill pesticides on skin or clothing. If they are accidentally spilled,
remove contaminated clothing immediately and wash the contaminated skin thoroughly. Wash hands and face and change to clean clothing after applying pesticides. Also wash clothing each day before re-use and separate from the family laundry. Do not spray with leaking hoses or connections. Do not use the mouth to siphon liquids from containers or to blow out clogged lines, nozzles, etc. SEE DOCTOR IF SYMPTOMS OF ILLNESS OCCUR DURING OR AFTER THE USE OF PESTICIDES. A list of Poison Control Centers located in and around Virginia is included in this guide.
Apply Pesticides Carefully – Successful pest control requires application of the correct amount of pesticide uniformly over a targeted area. With most pests, application is a precise operation requiring reliable equipment. Timeliness may also be critical. Many herbicides have narrow ranges of selectivity. At the suggested rates of application they
will generally control weeds without damaging the crop, but at a slightly higher rate they may damage or kill the crop.
Dispose of Pesticides Correctly – All pesticides should be disposed of according to container directions. All empty containers should be triple rinsed (or equivalent), crushed, and disposed of as directed by the product label. Rinsate should be placed in the spray tank at the time of mixing. Left-over dilute pesticides should be used according to label directions. Left-over concentrates should be disposed of according to EPA Guidelines only after exhausting other options. Amounts of chemicals that do not qualify for disposal under these guidelines must be hauled by an approved hazardous waste handler at a cost to the owner of the chemical.
Pet, Fish, and Wildlife Protection – To protect fish and other wildlife, do not apply known harmful pesticides to streams or areas where drainage may be expected to enter waterways. Incorporate all granular pesticides into the soil to prevent birds and other animals from eating granules. Scout fields for dead animals and birds before and after application. Remove any carcasses to prevent poisoning of birds-of-prey and scavengers. Report any wildlife poisonings to the Virginia Game Commission. Be aware of bee cautions; see section to follow on protecting honeybees from pesticides.
Cover food and water containers when treating around livestock or pet areas. Do not discard leftover materials into drainage channels. Confine chemicals to the property and crop being treated.
Drift and Volatility of Herbicides – Drift can be a problem with any pesticide; however, drift of herbicides is the most commonly encountered cause of pesticide damage to susceptible crops. No pesticide can be applied by either aerial or ground- equipment without some drift. Spray drift is influenced by air movement, droplet size, and distance traveled by spray before reaching the target area. For minimum drift, application should be made as close to the ground as possible, when air movement is at a minimum, and using spray nozzles which eliminate fine droplets. In some instances, spray additives or thickeners may be used to improve application to the target area and to reduce drift.
Some herbicides, such as highly volatile esters of 2,4-D (e.g., isopropyl and butyl esters), are capable of causing injury to adjacent crops by movement in the vapor phase after the spray has dried on the plant or soil surfaces. Use the amine, low-volatility ester or oil-
soluble amine formulations of 2,4-D to reduce the possibility of vapor drift. The farmer and the applicator are liable for damages caused by drift or volatility.
Decontamination of Sprayers Used for Herbicides – Tobacco, grapes, tomatoes, garden vegetables, fruit trees, ornamental plants, and many other crops are particularly susceptible to 2,4-D and related growth-regulating chemicals. Do not spray sensitive plants with a sprayer that has previously contained these chemicals. For less sensitive plants, sprayers may be adequately cleaned by using household ammonia. After flushing the sprayer, a 2% solution (1 gal to 50 gal of water or 1 cup to 3 gal water) should be allowed to remain in all parts of the sprayer for 24 to 48 hours. Rinse afterwards several
times with water, the last time immediately before re-use. Wettable powders, salts, and amine formulations can usually be removed by repeated washing with water.
Selection of a Pesticide and its Formulation – Two or more pesticides may be equally effective in a given situation. Also, the same chemical may be available in a variety of formulations. Your selection of a pesticide and its formulation will be determined by the (1) pest species involved, (2) availability of the pesticide, (3) type of equipment at your disposal, (4) hazards to humans, domestic animals, wildlife, and desirable plants, (5) relative total costs of materials and application, and (6) time of application.
All recommended rates of application are based on the amount of active ingredient in a given product. Many commercial products vary in the percentage of active ingredient. The label will give the exact amount of active ingredient in the container and the amount of product to be used in a given area.
To make an accurate cost comparison, it is wise to calculate the cost per area. In general, more concentrated products are more economical.
Granular formulations of many pesticides are available. In comparison to sprays, granular pesticides offer both advantages and disadvantages. Some of the advantages are: simpler application (no water or mixing required,) less drift, and a tendency toward longer activity in the soil. The problem of accurate calibration of granular equipment and the higher per-acre cost of granular pesticides may offset these advantages. Variation of particle size for different products, varying rates of application, and varying percentages
of active ingredients complicate calibration of granular materials. More concentrated materials are usually more economical but errors in calibration are more critical. Calibration charts are available from manufacturers of granular applicators. All steps suggested by the manufacturer should be followed for obtaining correct rates of application. Recently, insecticide granulars have come under regulatory pressure due to their potential harm to non-target species when not incorporated into the soil.
Fungicide granules may be incorporated with soil-less media for growing ornamentals in containers. It is important that the granules be thoroughly mixed, preferably with a rotating drum-type mixer. Because the vapor pressure of granular fungicides is low, it is important that the granules be incorporated uniformly to assure treatment of the entire soil volume.
Tank Mixes of Pesticides
If tank mixes are to be used, the following suggestions (taken in part from a Virginia Agricultural Chemicals Report dated 9/81) are offered:
1. For a pesticide to be used as a tank mix, one of the following criteria must be met:
1. The use is indicated on the label of one or more EPA registered products.
2. The use is covered by state registration.
3. The use has been tested and recommended by Agricultural Experiment Stations.
2. Check labels of products to be mixed to make sure that there are no explicit restrictions against mixing with other chemicals.
3. Make sure products to be mixed are labeled for the use intended and not to exceed labeled rates.
4. When mixing two or more pesticides, make sure you follow all restrictions for each chemical.
5. Make sure you are aware of your responsibilities when using a tank mix. (Read the warranty.)
6. Make sure you actually need a tank mix. Many times, a single pesticide is adequate.
7. Limit products in a mixture to no more than three to avoid increased possibility of crop injury or reduced effectiveness or both.
8. The private applicator or grower should mix the products in the field. If the dealer or his personnel deliver a label-prohibited tank mix, it is illegal and could place liability for any damages on the dealer and grower.
9. The final responsibility on the use of tank mixes lies with the user.
The Role of the Pesticide Industry in Safe Pesticide Use
Issues covered in this section include: the current need for pesticide use and approaches for control.
To keep costs at a minimum and production high, intensive management of forest and agricultural resources is required. Chemical pesticides are the most effective means for
protecting these investments, as biological controls are usually too slow-acting to be practical.
The environmental risk associated with pesticide use can be lessened with control measures. As mentioned previously (see paper 1), research during development, control by legislation and guidelines for use are important to balance pesticide benefits with environmental cost.
CONCLUSION
There were several issues dealt with in the sources on which the separate authors concurred. Pesticides are a necessary evil which require regulation to minimize their negative impacts on the aquatic environment. The regulatory process in Canada is a good one, which will need continuous improvements to deal with changing issues and information.
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