This appendix provides information on selecting the proper pesticides and using them safely, effectively, and legally. The inclusion of any pesticide name is for educational purposes and does not imply an endorsement of that product. We do not attempt to give specific chemical recommendations, but we do summarize basic concepts and principles for gardeners to use when considering the use of pesticides.
Pesticides are substances or mixtures of substances used to manage pests. The suffix “cide” means to kill, and “pest” refers to an unwanted living organism. Pesticides include herbicides, insecticides, fungicides, miticides, nematicides, and other such formulations. The first syllable of each word for these pesticide types indicates the intended target. For example, insecticides kill insects, herbicides kill weeds, and rodenticides kill rodents. Pesticides can also kill nontarget organisms. For example, some insecticides can kill earthworms, fish, or plants when misused. Some types of pesticides don't have the "cide" suffix. Examples include repellents and pheromones.
Safe handling of pesticides involves a combination of knowledge, common sense, and the ability to read and follow directions. Misuse of pesticides can result in poisoning of the gardener, family members, neighbors, pets, and/or the environment. Pesticides should only be applied as part of a comprehensive integrated pest management (IPM) program. Read more about IPM in chapter 8. Before applying any pesticide, answer several questions:
- Which pests or pest problems exist?
- Is the problem the result of an unfavorable environment?
- Can the problem be corrected using other methods?
- Which pesticide will effectively manage the pest, will cause the least damage to beneficial insects and the environment, and will be least hazardous for the applicator to use? Have you considered runoff potential, chances of leaching into groundwater, chemical half-life (how rapidly it degrades), and toxicity to nontarget organisms?
- When and how much pesticide should be applied?
Many home gardeners do not know the answers to these questions. As a consequence, some gardeners may make too many pesticide applications or apply the wrong material at the wrong time, in the wrong manner, and in the wrong amount. In addition to wasting money and time, improper pesticide use can endanger the environment by killing beneficial insects, poisoning wildlife, and contaminating soil, water, and air. Problems such as these have led to many new regulations, including banned use and restricted use of pesticides.
General Pesticide Safety Guidelines
One way that pesticides are grouped is by their chemical nature. In chemistry, “organic” refers to carbon-based molecules. This is different than the way “organic” is commonly defined by gardeners and by the National Organic Standards Board. In other words, organic as a production method has nothing to do with organic as a chemical term. The most common pesticide groups are inorganics, plant-derived organics, microbials, and synthetic organics. Additional pesticides include horticultural oils, soaps, and byproducts.
These pesticides are made from minerals such as arsenic, copper, boron, lead, sulfur, tin, and zinc. Copper and sulfur are commonly available in garden supply shops.
Plant-Derived Organic Pesticides
These pesticides consist of natural compounds that come directly from plants. A common example is pyrethrum, which is made from the flowers of some Chrysanthemum species. Other plant-derived products include neem, nicotine, and red squill. Be careful with all pesticides; natural products can be as toxic to humans and other organisms, or even more toxic, than some manmade pesticides.
These pesticides consist of microscopic organisms—including bacteria, fungi, nematodes, and viruses—that attack pests. Most of these can be applied with conventional application equipment. A few microbial insecticides multiply and spread after application and may become established in the garden or lawn, but most of them require repeated applications to be effective. The most commonly encountered microbial pesticide is the bacterium Bacillus thuringiensis (Bt), which is often applied to control caterpillars. Bt does not spread after application, whereas Paenibacillus popilliae, used to manage Japanese beetle grubs, can. In general, microbial pesticides are less toxic than other pesticides for gardeners, beneficial insects, and the environment.
Synthetic organics, those that are man-made, are the largest group of pesticides used by gardeners and farmers. An example is permethrin which is a synthetic compound similar to the plant-derived pyrethrum.
Some Pesticide Definitions
Contact pesticides kill pests that touch them. Most synthetic organic pesticides work in this manner. Insects are affected simply by walking across a treated surface.
Fumigants are gaseous pesticides that kill the pest when it inhales or absorbs the chemical. Fumigants are toxic to people and animals.
Nonselective pesticides are toxic to the targeted pest and many other plants or animals. Most synthetic organic insecticides are nonselective. For example, a pesticide containing carbaryl can be used to kill Colorado potato beetles, but it also kills bees and many other types of insects. Herbicides containing the active ingredient glyphosate kill nearly any type of plant. Gardeners must exercise extreme caution when using nonselective pesticides and always follow labeled instructions.
Protectants are applied to plants, animals, structures, and products to prevent entry or damage by a pest. To prevent termite damage, for example, termiticides are typically applied to the soil surrounding a building before termites are discovered.
Selective pesticides are more toxic to some kinds of plants or animals than to others. For example, a broadleaf herbicide kills dicot weeds but not grasses. Microbial pesticides affect specific species of insects.
Stomach poisons must be eaten by the pest to be effective. They are generally effective if you are trying to encourage beneficial insects that do not feed on the sort of plant you have treated. Some stomach poisons, however, can also kill by contact.
Systemic pesticides are soluble in water and can be absorbed by a plant and transferred through some, or all of, the plant’s tissues, including its leaves, stems, roots, flowers, nectar, and pollen. The pesticide then poisons any insects that feed on the plant. Neonicotinoids are nicotine-based systemic insecticides.
The mixture of active and inert ingredients included in a product is called a pesticide formulation (Figure B–1). The active ingredient in a pesticide product is the substance that actually controls the pests. Inert ingredients, also known as “inactive” or “other” ingredients, may make the active ingredient easier to mix with water, safer to handle or apply, or allow the pesticide to be applied with various types of equipment. Inert ingredients are regulated to a limited degree but can also pose a hazard to the person applying the pesticide or to plants. Formulations may be liquid, gaseous, or solid. Some formulations are ready-to-use, and others must be diluted with water. Many pesticides are available in more than one formulation.
Solutions are pesticides that dissolve readily in liquid, such as water or a petroleum-based solvent. Aerosol pesticides consist of liquids that contain active ingredients in solution or emulsion. The liquid solution or emulsion forms fine droplets when driven through a small nozzle by a pressurized gas. Aerosols often contain more than one active ingredient in low concentrations. Many aerosols come in disposable dispensers. Aerosols are most frequently used indoors, but a few are sold for outdoor use. Based on the amount of active ingredient, ready-to-use aerosols are typically expensive in comparison to other ways to purchase pesticides.
- Dusts are typically ready-to-use and combine the active ingredients with a dry inert material, such as talc, clay, nut hulls, or volcanic ash. The amount of active ingredients usually ranges from 1% to 10%. Some active ingredients are formulated as dusts because they are safer for crops in that form. Although they resemble wettable powders, dusts must always be used dry. Dusts drift easily; be careful not to let the chemical drift into nontarget areas, and wear goggles and a dust mask to avoid inhalation. Dusts leave visible residues that may be objectionable in some situations.
- Wettable powders are dry, finely ground pesticide formulations that look very similar to dusts. Unlike dusts, however, they are made to mix with water and are applied with a sprayer. Most wettable powders are more concentrated than dusts. They contain 15% to 95% active ingredient and often include 50% or more active ingredient. Because wettable powders form a suspension in water rather than a true solution, good agitation (shaking) is needed in the spray tank. Most wettable powders are less toxic to plants and people, but they leave a visible residue that may be objectionable in some situations.
- Granules and pellets are created in the factory by applying a liquid formulation of the active ingredient to coarse particles (granules) of some porous material, such as clay, corn cobs, or walnut shells. The pesticide is absorbed into the granule or coats the outside of it, or both. Granule particles are larger than dusts. The amount of active ingredient ranges from 2% to 15%. Granular formulations are less likely to drift than sprays or dusts. Many types of granules, however, can present hazards to birds. Granular formulations are most often used as soil treatments, and they may be applied either directly to the soil or over plants. They do not cling to plant foliage but may be trapped in the whorls (spiral growth) of some plants. With the exception of water dispersible granules, granular formulations should never be mixed with water. Some granules may need rain or irrigation after application for activation of the pesticide. Pellet formulations are very similar to granular formulations, except that particles are generally larger and have a consistent size and shape.
- Baits are edible or attractant substances mixed with a pesticide. The bait attracts pests, and the pesticide kills them after they eat the formulation. Baits are commonly used to control slugs, snails, rodents, ants, and some other insects. The amount of active ingredient in most bait formulations is less than 5%. Nontarget animals should be restricted from any area where bait traps are set. Baits are often put in bait stations to prevent access by all but the target pest. Household pets, squirrels, and chipmunks will eat bait designed for rats and mice. Dogs and cats are also attracted to slug bait.
To determine the best buy, look at both the concentration and quantity of active ingredient. A formulation with 10% active ingredient has twice the concentration as one containing 5% active ingredient. A frequent error that most home gardeners make is to purchase too much product. Do not purchase more than that needed in one season. Some pesticide products deteriorate with time. Excess products can create safety problems in storage and disposal.
Pesticides may be combined with other products. Weed-and-feed fertilizers are classified as pesticides. They are mixtures with relatively small concentrations of pesticides (herbicide) added to a fertilizer. Landscape fabrics can be impregnated with pesticides, or pesticides can be sprayed on mulch. Check the labeling (the label and any pamphlets that come with the product) to find out what pesticide has been added and how to use the product.
An adjuvant is a chemical already added to the pesticide formulation or spray mixture to increase its effectiveness or safety. A suspension agent added to a spray solution helps mix oil and water so they can be sprayed on plant surfaces. Some of the most common adjuvants are surfactants that alter the dispersing, spreading, and wetting properties of spray droplets. Examples of adjuvants include the following:
- Wetting agents enable wettable powders to be mixed with water.
- Emulsifiers enable petroleum-based pesticides to be mixed with water.
- Spreaders enable pesticides to form a uniform coating over the treated surface by reducing the surface tension of the spray droplets.
- Stickers improve the pesticide's ability to adhere to plant surfaces. Some stickers protect the spray from the effects of wind and rain, thus extending the active life of the pesticide. Most fungicides benefit from the use of stickers.
Making Pest Control Decisions
Adopt an IPM method that prevents or manages a problem using the most effective, environmentally friendly, and economical control measure(s). Research confirms that cultural, mechanical, physical, biological, and chemical management techniques exist for most pest problems. Begin with mechanical, physical, cultural, and biological management techniques, which are generally more cost-effective and environmentally friendly. Quick-acting chemical treatments, with the exception of some emergency fungicide treatments, should not be treated as a substitute for sound gardening practices.
Chemical recommendations should come from the North Carolina Agricultural Chemicals Manual, recent Extension publications, or current research updates from NC State University. Before following home remedies, check with your county NC State Extension center to identify potential benefits and harm.
When pesticides are applied is as important as what is applied. Review information for the best time of day, time of year, or point in a pest’s life cycle for treatment. Read the label. Remember it is illegal to use or recommend the use of a product in a manner, rate, or on plants inconsistent with the label. Do not use pesticides on a fruit or vegetable plant unless the pesticide is specifically labeled for use on that crop or is labeled for use on all fruits and vegetables. Be sure to review the label to identify the safe minimum interval between spraying and harvest.
The "label" refers to the printed information on or attached to the pesticide container (Figure B–1). Often there is more information available than will fit on the product package. The term "labeling" includes the label plus all information that is received from the company or its agents about the product. This includes supplemental brochures or flyers that accompany the product. Following the directions on the label is required by law.
Pesticide labeling can be complicated, but it is important to understand the directions and precautions to use the product safely and correctly. Read the labeling with each purchase of a pesticide product. Instructions, precautions, and restrictions may have changed since the last time the product was used. Certain information must appear on the pesticide labeling. Items required are listed here and described in the sections that follow:
- Brand name, type of pesticide, and formulation
- Ingredient statement
- EPA registration and establishment number
- Signal words and symbols
- Precautionary statements
- Hazards to humans and domestic animals
- Environmental hazards
- First aid
- Directions for use
- Waiting period (if any)
- Preparation instructions and directions for use
- Protective clothing needed (Figure B–2).
- Storage and disposal
- Name and address of manufacturer
Each company has a brand name for each of its products. The brand name is used in advertising; it appears plainly on the front panel of the label. Most companies register each brand name as a trademark and do not allow other companies to use that name. Manufacturing brand names are sometimes useful but can also be deceptive in identifying the active ingredient. For example, Liquid Sevin® refers to the active ingredient carbaryl. Sevin® is the manufacturer’s name for carbaryl. Brand names such as Black Flag Ant and Roach Killer® or Ortho Flying Insect Spray® are not associated with a particular active ingredient. In other words, the U.S. EPA does not register products by brand name.
Type of Pesticide and Formulation
The type of pesticide is usually listed on the front panel of the pesticide label. This short statement indicates in general terms what the product controls.
- Insecticide for control of certain insects on fruit, nuts, and ornamentals
- Herbicide for the control of woody brush and weeds.
Some labels will also indicate the product formulation. The formulation may be named or abbreviated.
Every pesticide label must list the active ingredients and the percentage of each active ingredient found in that product. Inert ingredients are not usually named, but the label must show what percentage of the total contents they make up. The ingredient statement must list the official chemical names or chemical names of the active ingredients.
The chemical name identifies the chemical components and structure of the pesticide’s active ingredient. Because chemical names are usually complex, many are given a shorter common name. Only those common names officially accepted by the EPA may be used in the ingredient statement on the pesticide label. The EPA requires that a particular common name be associated with a specific active ingredient. The official common name is usually followed by the chemical name in the list of active ingredients. Purchase pesticides according to the common or chemical names to be certain of getting the right active ingredient, no matter what the brand name or formulation.
EPA Registration Number and Establishment Number
An EPA registration number must appear on all pesticide labels (except minimum risk Section 25(b) products). It indicates that the pesticide product has been registered and its label approved by the EPA.
An EPA establishment number (for example, EPA Est. No. 122-NC-2) must also appear either on the pesticide label or container to identify the facility that produced the product. This is necessary in case a problem arises or the product is found to be adulterated in any way. The “NC” in the establishment number indicates the product was manufactured in a specific facility in North Carolina.
Signal Words and Symbols
The signal word and symbol on the pesticide labeling tells how toxic the pesticide is to humans. It is important to become familiar with the meaning of signal words and symbols.
Scientists determine the dosages that will cause death of laboratory animals when swallowed, when applied to the skin, or when inhaled, as well as levels that will cause irritation to the skin or eyes. The exposure route by which the product is graded the most toxic to humans will determine the signal word that must appear on the label. Additionally, the labeling of all highly toxic materials usually carries a skull and crossbones, along with the words “Danger” and “Poison”. These products are rarely available to consumers.
The amount of pesticide that will injure or kill a pet or a child may be much less than the amount that will injure or kill an adult. All products must bear the following statement: "Keep out of reach of children."
|Signal Word||Toxicity||LD50a||Approximate amount which, when swallowed, will kill the average-sized adult|
|Danger - POISON||Indicates extremely toxic compounds when consumed, inhaled or absorbed through the skin or eyes. (Label must have skull and crossbones symbol.) Fatal at very low doses.|
|Danger||Highly toxic||Up to and including 50mg/kg||A taste to a teaspoon|
|Warning||Moderately toxic||50–500mg/kg||A teaspoon to two tablespoons|
|Cautionb||Slightly toxic||>500mg/kg||An ounce to more than a pint|
|a LD50 is the approximate amount, which when swallowed will kill 50% of the animals tested.|
|b There is an additional category less toxic than Caution. No signal words are required on pesticide products, which are determined by the EPA to be exempt or minimum risk. These are generally regarded as safe.|
The Environmental Protection Agency (EPA) categorizes every use of every pesticide as either "unclassified" or "restricted use." A pesticide categorized as restricted-use carries a greater risk than a pesticide categorized as unclassified. Restricted-use pesticides can be purchased and applied only by a certified applicator who has been trained to use these pesticides safely and effectively or by someone acting under a certified applicator’s supervision. Labels will state "Restricted-Use Pesticide" in a box at the top of the front panel. The North Carolina Agricultural Chemicals Manual includes unclassified and restricted-use pesticide recommendations. Materials available to home gardeners are customarily unclassified or general use pesticides, which have lower toxicity than restricted-use pesticides but can still cause harm. Always read and follow the label directions closely.
Hazards to humans (and domestic animals). This section of the label indicates the ways in which the product may be poisonous to people and animals. It will contain statements such as these: "Harmful if absorbed through the skin," or "Avoid contact with skin or eyes." The label will also specify any special precautions that the user needs to take, such as the kind of protective clothing recommended.
Environmental hazards. Some pesticides are particularly hazardous to bees, fish, birds, or other wildlife. This portion of the labeling warns of environmental damage that may be caused by the pesticide. Examples include the following warnings: "Do not apply when runoff is likely to occur." “Do not apply when bees are active."
Physical and chemical hazards. Certain pesticide formulations may be flammable, explosive, or present special chemical risks. Common statements in this section are "Keep away from heat, sparks, or open flame," or "Do not incinerate."
First aid (Figure B–3). If a pesticide can be harmful, this segment of the labeling provides instructions for first aid. It will also advise when medical attention is necessary in case of exposure to the pesticide. Always consult the label before administering first aid to poison victims because the wrong first aid measures can cause additional injury. This section of the label may also instruct physicians on how to treat poison victims. If a poison victim needs to be taken to a hospital, always take the pesticide label.
Directions for Use
To use any pesticide product safely and effectively, follow the pesticide instructions or directions for use (Figure B–4). This section of the label will include a reminder that it is a violation of federal law to use or recommend the use of a pesticide in a manner inconsistent with the labeling. The directions for use will include the following information:
- Pests that the product can be used to control. It is illegal to apply the pesticide to pests not listed on the label.
- The crop, animal, or other sites for which the product is registered. It is illegal to apply pesticides to sites not listed on the label.
- How to mix the pesticide and how much to apply. It is illegal to apply a pesticide at greater than the labeled rate. Application below the labeled rate is allowed but may not provide effective control.
- How to apply the pesticide, including when and where to apply. Pesticides must not be applied in a manner contrary to these instructions.
- How often to apply. Pesticides may not be applied more often than the label allows.
Most pesticides packaged for home use will indicate how many level teaspoons or tablespoons of pesticide are needed per gallon of water. Some labels may indicate how many ounces of pesticide are needed per gallon of water. Those labels will also state that 1 fluid ounce equals 2 tablespoons.
Read the label to see how long people and pets should be kept out of the treated area (the re-entry interval or REI). If no time is listed, keep people and pets away at least until the sprays have thoroughly dried. If the pesticide was applied to a food crop, check the label to see how long to wait before harvesting (the pre-harvest interval or PHI); this is the time required for the residue to degrade to safe levels for consumption.
Select the right equipment, use it correctly, and maintain it properly.
Compressed air sprayers (Figure B–5). Compressed air sprayers are inexpensive and simple to operate, but the sprayer needs to be shaken regularly to provide agitation. Look for a tank with a large opening; it will be easy to fill and clean. Sprayers come in several sizes from 1 quart to 5 gallons; buy the size most appropriate for specific needs. Sprayers can be made of plastic, stainless steel, or galvanized metal. Galvanized metal sprayers have to be cleaned carefully or they will corrode.
Fill the tank not more than three-quarters full of spray material. This leaves an air space at the top for building up air pressure with the pump. Compressed air sprayers are easy to understand, and most homeowners can repair them. Look for replacement parts at local garden supply stores. Use caution when opening the sprayer if any pressure remains in the tank. After each use, flush out the tank, lines, and nozzles. Wash out the sprayer with detergent and water when switching pesticides to avoid contamination. Make sure to wear protective clothing when using a compressed air sprayer.
Phenoxy herbicides, such as 2,4-D, are active in very low concentrations; residues that remain in the tank even after cleaning can still injure plants. It is best not to apply other pesticides with a sprayer that has been used with phenoxy herbicides. One strategy is to have a separate sprayer for herbicides and another one for insecticides and fungicides.
Backpack sprayers (Figure B–6). These are compressed air sprayers that are carried as a backpack. The capacity of these sprayers is usually 3 gallons to 4 gallons. All models have a built in spray pump handle that makes it easier to maintain good pressure while spraying. Some disadvantages of backpack sprayers are (1) they require more care about leaks because the sprayers rest on the body, and (2) they cost more than other sprayers. As a result, backpack sprayers usually are not practical unless a large area is to be sprayed. Make sure to wear protective clothing when using a backpack sprayer.
Hose-end sprayers (Figure B–7). These are small, inexpensive sprayers designed to be attached to a garden hose. A small amount of pesticide is mixed with water and placed in the container attached to the hose. All hose-end sprayers should be equipped with an anti-siphon device to prevent backsiphoning of toxic materials into the water supply. Problems can result from poor spray distribution and clogged nozzles. Also, the pesticide-water mixture can be inaccurate because it is determined by water pressure. In general, hose-end sprayers are not encouraged because of their inaccurate application rate and the likelihood of chemicals being applied in areas where they are not needed. Make sure to wear protective clothing when using a hose-end sprayer.
Hand dusters (Figure B–8). Hand dusters may be as simple as a shaker can or may include a squeeze bulb, bellows, or a fan turned by a hand crank. Pesticides applied as dusts require no mixing, and dusts penetrate well into tight spaces. It is difficult, however, to obtain good coverage of foliage, and the dust drifts with a slight breeze. Make sure to wear protective clothing, including a face mask, when using a hand duster.
Granular applicators (Figure B–9). For home use, granular applicators usually consist of a shaker can for small areas or a spinning disk powered by a hand crank, or the wheels on a push spreader, for broadcast applications. Granular formulations are ready-to-use, do not drift as easily as some powder formulations, and are relatively easy to use. Make sure to wear protective clothing when using a granular applicator.
Personal Protective Equipment
Body covering (Figure B–10). Wear at least a long-sleeved shirt and long trousers or coveralls and socks and shoes or boots when applying pesticides. The clothes should be made of closely woven fabric . Do not wear leather clothing because leather tends to absorb and retain pesticides. Wear trousers outside boots to keep pesticides from getting inside.
Gloves (Figure B–11). Most pesticide exposure occurs through the hands and forearms. Hot, sweaty skin with cuts or abrasions allows more rapid penetration. When handling concentrated or highly toxic pesticides, wear liquid-proof, chemical resistant, neoprene gloves that are long enough to protect the wrists. Unlined gloves are preferred. Unless spray is being directed upward, wear sleeves outside of the gloves to keep pesticides from running down the sleeves and into the gloves. Glove lining is hard to clean if a chemical gets on it. If spray is being directed upward, the sleeves should be inside the gloves to prevent pesticides from running into the sleeves. Labels have been updated with new safety information. Older labels do not always mention the use of gloves and goggles when mixing and applying pesticides.
Goggles (Figure B–12). Eyes readily absorb and are very sensitive to the chemicals in some pesticide formulations, especially concentrates. Wear shielded safety glasses or goggles when mixing pesticides or spraying pesticides upward. Labels have been updated with new safety information. Older labels do not always mention the use of gloves and goggles when mixing and applying pesticides. Use gloves and goggles anyway to be safe.
Shoes (Figure B–13). Wear liquid-proof boots or cover shoes with liquid-proof material. Leather and cloth absorb pesticides, and both leather and cloth are very difficult to clean.
Mixing is usually considered the most dangerous pesticide activity because mixing involves working with concentrated material. Be sure to wear gloves and safety glasses. Never eat, drink, or use tobacco while handling pesticides.
Before mixing a pesticide, always read the labeling. Inspect the sprayer, duster, or spreader to see that it is functioning properly. There should be no loose or leaking hoses or connections. The cover gasket on a sprayer should fit securely. Partially fill the sprayer with water, and test it to make sure that the nozzles are not clogged. Make sure there are no leaks and that the tank holds pressure.
When preparing a wettable powder for spraying in a compressed air or pump-type applicator, place the required rate of pesticide into a quart jar half filled with water and mix well. Pesticides that contain surfactants (spreader-stickers, wetting agents) make mixing easier by helping to maintain the homogeneity of the mixture. Next, pour the solution into a sprayer tank containing three-quarters of the water needed to spray the intended area. For example, if 4 gallons of spray solution are needed, put 3 gallons of water in the tank, add the quart of water-pesticide solution, and then finish filling the tank with water to make the 4 gallons of spray solution. Shake the tank thoroughly before spraying and agitate it frequently while spraying to keep the pesticide from settling. Apply to foliage until just before it drips off; covering all surfaces.
When mixing pesticides for hose-end applicators, place the required amount of pesticide and a small amount of water into the reservoir jar of the applicator. Stir until thoroughly mixed. Fill the unit to the desired volume, agitate, and spray according to directions. Keep the mixture agitated during spraying. After use, clean and store the application equipment properly.
Soil application often involves using soil drenches, granules, or dusts. Incorporate dry formulations (granules) into the soil with a rototiller or rake. For drenches, mix by adding the required amount of pesticide and water in a bucket. Create a small dike, 3-inches to 4-inches high, just beyond the leaf zone (dripline) of the plant. The dike should help keep the solution within the desired area.
Two or more pesticides that can be mixed together for a single application are said to be compatible. Sometimes the pesticides are formulated together by the manufacturer. Not all pesticides are compatible with each other. Some mixtures may be toxic to plants. Check the pesticide label first to see if there are any restrictions or allowable mixtures. Only mix pesticides if mixing them is recommended on the label.
When a pesticide is applied to a given area, the usual approach is to mix a certain amount of material and apply the spray to the problem area. Some pesticide labels give application rates per 100 or 1,000 square feet. Make calculations to convert the rate given to determine how much to use on a small area using Table B–2. Be sure to pay attention to coverage statements. Mixing and applying can be confusing when the labeling does not state the number of gallons to use over a specific area.
To make sure the correct amount of pesticides is being applied, calibrate the sprayer. Keep in mind that spray volume varies with sprayer nozzle size, walking speed, and spray pressure. Calibration of drop and rotary spreaders can be found on the Internet home page for the spreader manufacturer. Follow the steps below to calibrate a compressed air sprayer.
When applying pesticide to an area measured in square feet, calibrate the sprayer by staking out a 1,000-square-foot test plot on a surface similar to the treatment site.
Step 1. Fill the sprayer tank half full with water (no pesticide).
Step 2. Record the number of seconds it takes to spray the test plot evenly while walking at a comfortable, steady pace. Consider spraying the test plot in this manner two or three times and average the times.
Step 3. Fill the sprayer half full with water and spray into a container for the average time from Step 2. Measure this water in ounces. The number of ounces equals the amount of spray used to cover 1,000 square feet.
This number helps calculate the amount of pesticide and water needed to treat the target area.
Example 1, Lawn Treatment: After using IPM techniques, you determine your lawn area needs to be sprayed with a fungicide.
1. Calculate square footage to be treated: The lawn area is 45 feet by 80 feet, or 3,600 square feet.
2. Identify the application rate: The labeled application rate for the fungicide is 2 ounces per 1,000 square feet.
3. Calibrate the sprayer using a 1,000 square foot test plot area. It takes 90 seconds to cover the plot. The amount of water collected in 90 seconds is 65 ounces. The sprayer output is 65 ounces per 1,000 square feet.
4. Determine the total spray mixture needed:
|X oz||65 oz|
|3,600 sq ft||1,000 sq ft|
X = 234 oz of mixture to cover 3,600 sq ft
5. Determine the amount of fungicide needed:
|X oz||2 oz|
|3,600 sq ft||1,000 sq.ft.|
X= 7.2 oz of fungicide to cover 3,600 sq ft
6. Determine the amount of water:
234 oz of total mixture – 7.2 oz of fungicide = 226.8 oz of water to cover 3,600 sq ft
|X gallons||1 gallon|
|226.8 oz||128 oz|
X = 1.77 gallons of water
Answer: To treat the lawn, add a little more than 7 ounces of fungicide to 1.75 gallons of water.
Example 2, Ornamental Treatment: After using IPM techniques, you determine your fruit trees need to be sprayed with an insecticide. The labeled rate for your insecticide is 4 ounces per gallon of water. You have six trees to treat. First calculate how much water needs to be sprayed to treat one tree: Add water to your tank and spray the tree as if you are spraying paint, timing the number of seconds it takes. You want adequate coverage, but do not want the insecticide to drip off the plant. Averaging the number of seconds it takes for a few sprays gives you more accurate results. Now spray the water into an empty container for that same number of seconds and measure the amount of water in ounces.
Number of trees to treat = 6
Seconds to spray one tree = 45 seconds
Amount of water collected in 45 seconds: 30 ounces
- Determine the total amount of mixture needed by multiplying the number of trees by the amount of water required to treat one tree.
- 6 trees × 30 oz = 180 oz
- Convert ounces to gallons: 180 oz divided by 128 oz = 1.4 gallons of mixture
- 6 trees × 30 oz = 180 oz
- Determine the amount of insecticide needed by multiplying the labeled rate by the total spray mixture.
- 4 oz per gal × 1.4 gal = 5.6 oz of insecticide
- Determine the amount of water needed by subtracting the amount of insecticide from the total amount of mixture 180 oz total mixture minus 5.6 oz. of insecticide = 174.4 oz of water
- 4 oz per gal × 1.4 gal = 5.6 oz of insecticide
Convert to gallons
|X gallons||1 gallon|
|174.4 oz||128 oz|
X = 1.36 gallons of water
Answer: Add a little more than 5½ ounces of insecticide to a little more than 1 1/3 gallons of water.
|Liquid Materials Approximate Rate|
|per Acre||per 1,000 Square Feet||per 100 Square Feet|
|1 pint||2¼ teaspoons||¼ teaspoon|
|1 quart||4½ teaspoons||½ teaspoon|
|2 quarts||3 tablespoons||1 teaspoon|
|1 gallon||6 tablespoons||1¾ teaspoons|
|25 gallons||4⅔ pints||14⅔ tablespoons|
|50 gallons||9¼ pints||1⅞ cups|
|100 gallons||9¼ quarts||3⅔ cups|
|200 gallons||18⅓ quarts||7⅓ cups|
|300 gallons||27½ quarts||5½ pints|
|400 gallons||9¼ gallons||7⅓ pints|
|500 gallons||11½ gallons||9¼ pints|
|Dry Materials Approximate Rate|
|per Acre||per 1,000 Square Feet||per 100 Square Feet|
|1 pound||0.37 ounce
|2 pounds||0.74 ounce
|3 pounds||1.1 ounces
|4 pounds||1.47 ounces
|5 pounds||1.84 ounces||0.18 ounce|
There is no good method for disposing of excess spray materials. Dusts and granules can be saved for the next application, but not liquids. The best solution is to mix only as much as needed for one application session. If, however, pesticide remains in the tank after a spray job is complete, use it up. Spray it on other crops or sites listed on the label. Never pour pesticides down a drain. It is possible for pesticides to stop the bacterial action in a septic tank or contaminate a municipal sewage system, surface water, or groundwater. Pouring pesticides in a storm drain or ditch will cause environmental damage.
Thoroughly clean the pesticide application equipment immediately after each use. Dust or granular spreaders can corrode rapidly if pesticide residue remains. Rinse sprayers three times, and spray a portion of the rinse material through the nozzle. A small amount of detergent in the first rinse helps remove any residue. Do not dump the rinse water in one place where it will be concentrated and may become a pollutant. Spray the rinse water over a broad area (listed on the label) so that the pesticide will be further diluted. Never pour rinse water down the drain or in a ditch or storm drain, as rinse water is toxic.
Once the sprayer is clean, disassemble the nozzle, remove the tank cover, make sure the hose and spray mechanism are drained, and allow the sprayer to air dry. After drying, reassemble the sprayer and store in a clean, dry location. Never clean nozzles with wire, knives, or other hard objects. They can damage the nozzle, which may change the spray pattern and delivery rate. Soft wood objects (such as toothpicks) or liquid solvents are recommended for cleaning nozzles.
Empty Pesticide Containers
Rinse empty pesticide containers at least three times. Pour rinse water into spray tanks and apply the pesticide-contaminated water to plants or the site as part of the spray solution. For glass and most plastic containers, replace the lid and place in the trash. If possible, punch holes in the containers and crush them to prevent further use.
Any pesticide for which the uses have not been suspended or canceled should be used if possible. If a pesticide has been suspended or canceled, or if the product cannot be used, call the NC Department of Agriculture and Consumer Services at (919) 733-3556 for disposal advice. The department may be able to pick up certain pesticides that cannot be legally used.
Cleanup any spills immediately. Vermiculite, oil absorbents, and even kitty litter can be used to soak up liquid spills. Report any large spills that cannot be easily managed to the NC Department of Agriculture and Consumer Services, Structural Pest and Pesticides Division by calling 919-733-3556. For example, a spill of a liter of premixed imidacloprid in a driveway can probably be hosed off into the surrounding landscape. Thirty pounds of lawn pesticide spilled in a shed or on a lawn requires a call to the NC Department of Agriculture.
The pesticide labeling will advise the kinds of protection that must be worn to avoid pesticide exposure. Shower after working with pesticides. Be sure to wash the entire body, including the hair. Wash immediately after any spill on the body.
Consider all clothing worn while handling or applying pesticides as contaminated. Handle with gloves. Wash separately from the family wash. Pre-rinse clothes worn during application of pesticides before washing them to help remove pesticide particles from the fabric. Wash the clothes in hot water with detergent. Wash only a few items at a time to allow for maximum agitation and water dilution. Do not wash other clothes with the clothing worn while applying pesticides. If only slightly toxic pesticides were used, one wash cycle is adequate. Run the washer through one additional cycle without clothes, using hot water and detergent to clean the machine. Line-dry clothes outside in the sun, if possible, to avoid contaminating the dryer. If the clothes are heavily contaminated with pesticide, dispose of them.
Pesticide Information Sources
If you need more information on pesticides, contact these sources:
Read pesticide labels for specific storage instructions. North Carolina pesticide storage regulations require that pesticides be stored in a place away from children and pets. A secure wood or metal cabinet or closet will serve the purpose.
Always store pesticides in their original containers, never in unmarked containers or containers that have held food or drink. Place dry products above liquid products (Figure B–14). Check pesticide containers often for leaks or breaks. If a container is damaged, replace it with another container that held exactly the same pesticide or with a new container. If a new container is used, transfer the labeling from the old one.
Store pesticides away from combustible materials, such as gasoline or oily rags. Do not weld or burn near the storage area. To prolong the effectiveness of a pesticide, store in dry, cool (but above freezing) conditions, out of direct sunlight, with the container properly closed. Extreme heat can reduce the effectiveness of pesticides.
Some pest populations have become resistant to and are no longer killed by certain pesticides. Pesticide resistance develops from overuse of pesticides or continued use of the same or closely related pesticides. Such use results in killing the susceptible pests, leaving only the resistant ones to mate—resulting in a resistant population. When target pests develop resistance, formerly effective pesticides no longer work and pests become much more difficult to manage.
In the home garden, most pesticide failures are the result of not following labeling instructions, using the wrong chemical for the pest, spraying at the wrong time, or applying an inadequate amount. If the pesticide has not worked satisfactorily, ask these questions:
- Has the pest been correctly identified?
- Has the correct pesticide been used? Is the pesticide out of date? Was it stored correctly? Check the label.
- Has the correct dosage been applied? Check the label. Check the calculations used when mixing the pesticide.
- Has the pesticide been applied correctly? Check the label. Was spray coverage adequate and evenly applied? Was the pesticide applied at the wrong time or with the wrong equipment? The pest may have been in a life cycle stage that was not susceptible.
When a pesticide is applied to a crop or treatment site, a tiny proportion of the pest population (for example, one insect or weed in 10 million) may survive exposure to the pesticide due to its genetic makeup. When the pests that survive breed, some of their offspring will inherit the genetic trait that confers resistance to the pesticide. These pests will not be affected the next time a similar pesticide is used. If the same pesticide is applied often, the proportion of less-susceptible individuals in the population will increase.
To prevent resistance, rotate between pesticides that use different modes of action. For example, after using an insecticide that interrupts the insect’s reproductive cycle, switch to an insecticide that acts as a stomach poison.
For more information on pesticide resistance, click on the “Resistance” tab on the Pesticide Stewardship website.
Selecting the least toxic appropriate material and following label directions can prevent most potential damages. Improperly used pesticides can damage plants and harm people and the environment.
Phytotoxicity is injury to plants, which can range from slight burning or browning of leaves to death of the entire plant. Signs of chemical injury often do not appear until several days after exposure to the pesticide and can be confused with other plant problems. The likelihood of plant injury resulting from the use of a pesticide varies, depending on several factors:
- Chemical used: Some plants are sensitive to certain chemicals.
- Formulation: Emulsifiable concentrates, which contain solvents, are more likely to cause injury than wettable powders.
- Concentration: There is more room for error when using high concentrations.
- Combination of chemicals: Some mixtures cause injuries, whereas the same materials applied separately do not.
- Method of application: High-pressure applications may cause injury, whereas low-pressure applications would not.
- Amount applied: If too little is applied, the pest is not managed. Too much may cause plant damage.
- Growing conditions: Plants growing under stressful conditions (such as in a wet spot or in shallow soil) are more susceptible to injury than healthy plants growing in a location to which they are adapted.
- Growth stage or condition of the plant: Young, tender new growth tends to be more susceptible to injury than older growth. Some cultivars are more sensitive than others.
- Weather conditions at the time of application:
- Heat and drought stress can increase plant injury or reduce plant tolerance.
- Wind can increase drift, resulting in damage to nontarget plants.
- Rain can wash pesticide off, reducing effectiveness, and stormwater runoff can move pesticide into nontarget areas.
- Persistence: Some pesticides remain active in the soil or can be taken up into the plant and remain effective even after plant parts have been composted.
Injury can take several forms:
- Dead, burned, or scorched spots on or at the tips of leaves
- Misshapen fruit, leaves, or plants
- Unusual color
- Delayed maturity
- Poor germination
- Death of the plant
What information is required for a pesticide to be registered?
To be legally sold or used, pesticides must be registered by the Environmental Protection Agency (EPA). In evaluating a pesticide registration application, the EPA assesses a wide variety of potential human health and environmental effects associated with use of the product. Under the Food Quality Protection Act of 1996, the EPA must find that a pesticide poses a "reasonable certainty of no harm" before it can be registered for use on food or feed. For all pesticides other than reduced risk or food grade products used as pesticides, EPA requires the manufacturers to submit test data on the effects on humans and the environment.
The chance of being poisoned by a pesticide depends on the toxicity of the pesticide and the amount of exposure. Consider both of these factors whenever applying a pesticide.
There are two general types of toxicity, acute and chronic. Acute toxicity refers to the ability of a pesticide to cause illness or injury as the result of a single or short-term exposure. If illness occurs shortly after applying a pesticide, it may be acute toxicity or perhaps heat stress, which causes some similar symptoms. Chronic toxicity refers to the ability of a pesticide to cause illness or injury as the result of repeated, long-term exposure.
Some people can develop allergic reactions to certain pesticides just as some people are allergic to certain foods, fragrances, or pollens. Allergic reactions are not thought to occur during the first exposure to a pesticide. The first exposure may cause the body to develop a histamine response to a particular substance. A later exposure—sometimes a much later exposure—results in the allergic reaction. Certain people seem to be more chemically sensitive than others. These people are more likely to develop allergies to pesticides.
Pesticides enter the body by four main routes: through the mouth (by being swallowed), through the lungs (by being inhaled), through the skin (through wounds or direct penetration), or in the eyes (through contact).
Many pesticides can enter the body through the skin. Oil-based pesticides enter skin more easily than dusts or wettable powders. Because oil-based pesticides often have a high concentration of the active ingredient, use extra caution when mixing the concentrated material for application. Insecticides are generally more toxic to humans than fungicides or herbicides because many insecticides are designed to disrupt the nervous systems of animals.
Symtoms and First Aid
Early symptoms of poisoning by some of the common pesticides are similar to those of food poisoning or flu. Heat stress can cause symptoms that may be confused with pesticide poisoning. Become familiar with the "Statement of Practical Treatment" on the label before using the pesticide. Pesticides are most hazardous when handling concentrated forms (during mixing) but can still be hazardous during application. Heed the precautions listed on the labeling.
Initial Symptoms of Pesticide Poisoning
Advanced Symptoms of pesticide poisoning
First Aid Procedures
- If someone is exposed to a pesticide, take immediate action.
- If a pesticide is spilled, remove any contaminated clothing right away and wash skin thoroughly with soap and water. DO NOT use an abrasive cleaner, as this may allow the pesticide to penetrate the skin more easily.
- If pesticide enters the eyes, rinse the eye with clean water for 15 minutes.
- If the exposure is to pesticide vapors, get fresh air quickly.
- If someone exposed to a pesticide stops breathing, start artificial respiration immediately.
- If the pesticide is swallowed, read the label to see if you should induce vomiting. This is recommended for after swallowing some pesticides but is harmful after swallowing others. Never give anything by mouth to an unconscious individual.
- If you suspect that someone has been poisoned by a pesticide, follow the first aid advice on the pesticide label and IMMEDIATELY call a doctor or take the person to a hospital. Take all pesticide labeling, removing it from the container if possible. The doctor will need the information on the label to determine the proper treatment. The doctor may want to call the Carolina's Poison Center (1-800-222-1222) for specific information on treatment for pesticide poisoning.
After application, a variety of things can happen to a pesticide. Pesticides that move away from the release site may cause environmental contamination. Pesticide movement by air is usually called “drift.” Pesticide particles, whether from dusts, sprays, or vapors, may be carried off site in the air. Drift can be reduced by following label instructions, reducing pressure, and not spraying during windy periods. Volatilization of a pesticide occurs when it changes from a solid or liquid to a gaseous state after application. Following temperature recommendations on the label can reduce loss by volatilization. Because high temperatures increase volatilization, spray during the coolest part of the day.
Pesticide particles and liquids can also move off site because of spills, leaks, and improper equipment cleanup and pesticide disposal. Pesticides washed down a sink or storm drain could end up in the surface water supply.
A heavy rain after application increases the likelihood of surface water contamination by washing pesticides off the plant or from the soil. Sprays are less likely to cause problems from runoff than dusts or granular pesticide formulations. This is especially true if the spray has had time to dry before a rain. Soil runoff occurs when rainfall or irrigation rates exceed the rate at which water can be absorbed by the soil. Pesticides absorbed on soil particles move, too, when soil erosion occurs. Improving soil aeration, adding organic matter, reducing erosion, and paying attention to weather forecasts can help reduce pesticide contamination.
Leaching is the downward movement of pesticides and nutrients through the soil. Leaching is influenced by the solubility of the pesticide and by soil composition; pesticides are absorbed more readily by soils high in clay and organic matter and less so in sandy soils. Organic matter in soils can reduce pesticide activity to the point that higher rates are needed to achieve good pest control. Some pesticides become tightly held to soil particles and are not likely to move out of the soil and into water systems.
Pesticide Safety around Bees and Other Pollinators (Figure B–15)
After cultural needs of the plant are properly addressed and other IPM techniques have been exhausted, sometimes a pesticide is necessary. Pesticides can affect more than just the intended target, killing pollinators and natural predators. If you choose to use pesticides, take these precautions to protect beneficial insects:
Pesticides vary in the rate at which they break down and in the length of time they remain in the environment. Some are active for only a short period of time before being changed into other chemical compounds that are almost always less harmful than the original material. Persistent pesticides break down slowly and stay in the environment for long periods. Most persistent pesticides have very limited uses or have been removed from the market.
Once absorbed by plants, most pesticides are broken down into less toxic materials. When the plant or plant part dies, any remaining residues can serve as a food source for soil microorganisms, which break down the pesticides. This is the most common means of pesticide degradation. Warm, moist, well-aerated soil with a pH of 6.5 to 7.0 encourages high microbial activity. Through a process called photodecomposition, energy from the sunlight can also alter and degrade the chemical properties of pesticides.
- Is this pesticide hazardous to humans or pets? When used according to the label, pesticides are considered to have an acceptable risk.
- How long will this pesticide last on the shelf? (Is a pesticide I have on the shelf still usable?)Store pesticides in original containers, according to their label, in a cool, dry place. Most pesticides should have an expiration date printed on the label. Do not use a cancelled pesticide. Do not use pesticides if physical changes are noticed. For example, dry pesticides may lump or discolor, while liquid pesticides may crystallize or separate. Pesticides may degrade if frozen during storage.
- How long will this pesticide be effective once it is mixed? Pesticides cannot be saved after they have been mixed with water. The length of active time will depend on the quality of the water.
- How do I dispose of excess pesticides? It is best to use all of the pesticide in the appropriate manner. The NC Department of Agriculture and Consumer Services has a pesticide disposal assistance program. For more information on the program, please call (919) 733-3556 or your local government’s household hazardous waste program. If possible, avoid future pesticide storage problems by using an alternate control method that does not require a pesticide purchase. If pesticides must be purchased, buy the smallest quantity that will treat the area.
- How do I dispose of extra spray that has already been mixed? It is best to use the mixed spray on a site the pesticide is labeled to manage. Once mixed, the product cannot be stored.
- When can my pets go back in the yard after I have sprayed? The re-entry interval (REI) is listed on the label. Remember, the label is the law.
Wayne Buhler, Professor, Department of Horticultural Science
Steven Frank, Associate Professor, Department of Entomology
Contributions by Extension Agents: Alison Arnold, Danelle Cutting, Tim Mathews, Pam Jones, David Goforth
Contributions by Extension Master Gardener Volunteers: Linda Alford, Patty Brown, Marjorie Rayburn, Jackie Weedon, Karen Damari, Louise Romanow, Kim Curlee
Content Edits: Lucy Bradley, Associate Professor and Extension Specialist, Urban Horticulture, NC State University; Director, NC State Extension Master Gardener program,
Kathleen Moore, Urban Horticulturist
Copy Editor: Barbara Scott
Based in part on text from the 1998 Extension Master Gardener manual prepared by:
• Erv Evans, Extension Associate, Department of Horticultural Science
• Mike Linker, IPM Coordinator, Department of Crop Science
• Steve Toth, Extension Specialist, Department of Entomology
Publication date: Feb. 14, 2018
Other Publications in North Carolina Extension Gardener Handbook
- 1. Soils and Plant Nutrients
- 2. Composting
- 3. Botany
- 4. Insects
- 5. Diseases and Disorders
- 6. Weeds
- 7. Diagnostics
- 8. Integrated Pest Management (IPM)
- 9. Lawns
- 10. Herbaceous Ornamentals
- 11. Woody Ornamentals
- 12. Native Plants
- 13. Propagation
- 14. Small Fruits
- 15. Tree Fruit and Nuts
- 16. Vegetable Gardening
- 17. Organic Gardening
- 18. Plants Grown in Containers
- 19. Landscape Design
- 20. Wildlife
- 21. Youth, Community, and Therapeutic Gardening
- Appendix A. Garden Journaling
- Appendix B. Pesticides and Pesticide Safety
- Appendix C. Diagnostic Tables
- Appendix D. Garden Tools
- Appendix E. Season Extenders and Greenhouses
- Appendix F. History of Landscape Design
- Appendix G. Permaculture Design
- Appendix H. Community Gardening Resources
North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.