About Chemical Control
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Treatment Decisions
In landscape ornamental pest management, treatment decisions are often based on somewhat subjective criteria or threshold levels. If the objective is to produce plants free of pests and pest damage, pesticides are often applied automatically. If such preventive treatments are based on the historic seasonal occurrence of damaging pest populations they can be justified. However, a more prudent approach is to begin treatments when a pest or pest damage is detected. If the objective is to maintain vigorous, healthy plants, higher pest numbers and damage levels may be tolerable before treatment begins.
Proper Pesticide Selection
In choosing a pesticide, the landscaper should select a product that is specific to the pest to be controlled in order to spare beneficial arthropods. Systemic insecticides are less likely to affect predators and parasites on plant surfaces.Insecticidal soaps may spare hard bodied predaceous or parasitic arthropods. Microbial insecticides such as Bacillus thuringiensis products (Dipel®, Thuricide® and others) are target-specific for certain groups of insects. Specific miticides generally spare other arthropods. Vendex® is less toxic to predaceous mites.
Care must also be taken when using pesticides other than insecticides and miticides. Certain fungicides such as Benlate® will affect insectivorous fungi and other non-target organisms. Broad-spectrum insecticides often are useful when more than one pest is present, but they may cause a rapid resurgence of the primary or secondary pest. Pyrethroid insecticides are more harmful to parasitic wasps than to the pests listed on their labels. They are most effective against chewing insects.
Interpreting acute LD50 values. Another important consideration in choosing a pesticide is its toxicity. The LD50 value of an insecticide is commonly used as a measure of its toxicity. The LD50 is defined as the single dose of a chemical that results in a 50 percent mortality to a population within a specified time. It is expressed in milligrams (mg) of pesticide per kilogram (mg/kg) of the test animal's body weight. Generally, the lower the number the higher the acute toxicity.
Example: LD50 = 50 mg/kg
Sometimes this relative measure of toxicity is qualified by the species and sex of the test animal.
Example: LD50 male rat = 39 mg/kg
LD50 values can be further qualified by route of absorption or the way in which the pesticide was administered to the test animal.
Example: Acute oral LD50 male rat = 39 mg/kg
Example: Acute dermal LD50 male rat = 98 mg/kg
Acute oral (or dermal) LD50s for an experimental animal are useful indications of the probable relative toxicities of compounds to man and other warm-blooded animals. However, they are not an absolute representation of how much pesticide would be required to kill a human (as compared to a rat), nor the only important measure of the potential toxic effects which might occur with exposure to a given compound. A number of pitfalls must be considered when interpreting acute LD50 values. These include the following:
- Individual variation (genetic, age, sex, nutrition, hypersensitivity, etc.)
- Difference in route of exposure (oral, dermal, inhalation)
- Formulated versus pure chemicals (effects of solvents, types of formulations, etc.)
- Impurities of technical material
- Possible cumulative effects from multiple exposures to the same chemicals (chronic toxicity)
- Interactions with other chemicals in the individual's environment (drugs, environmental pollutants, etc.)
- Past or present disease status
LD50s tell us nothing of the possible chronic effects of these compounds nor possibilities of sublethal toxicity. A high acute LD50 (low acute toxicity) does not mean that a compound can be used carelessly, or that it is safe as long as exposure levels are below that of acute toxicity.
Since toxicity tests cannot accurately predict a chemical's effects on humans, the only way to reduce the hazard is to minimize exposure to any pesticide. The only indicator of toxicity of pesticide on a product label is the signal word (CAUTION, WARNING, DANGER).
Resistance Management
Some species of ornamental plant pests, including the green peach aphid, the sweet potato whitefly and the serpentine leafminer, have developed resistance/tolerance to pesticides. When a pesticide loses effectiveness some managers try using higher concentrations or more frequent applications to obtain acceptable control. These measures encourage resistance, however. Resistance is most likely to develop during long-term exposure to a particular compound, particularly in organisms with short life cycles and high reproductive rates.
To prevent resistance, managers should use pesticides (particularly nerve toxins) only when needed to prevent economic losses, and should use the lowest acceptable doses of pesticides. Once resistance has become evident, growers should rotate pesticide classes (pesticides with different modes of action) between pest generations. For more information, see the Insect Resistance Action Committee (IRAC) website.
Tank-mixing of insecticides is generally discouraged because it may cause pests to become resistant to all products in the mixture. However, there are times when tank mixtures can increase pesticide activity and lower the dose required. When a tank mix provides better control than the additive effect of each product applied separately, the mixture is said to be synergistic.
In most cases, tolerant or resistant arthropod strains are less fit than are susceptible strains. In the absence of the pesticide selection pressure, susceptibility will return to the population.
Get more information on insecticide resistance management at the Web site of the Insecticide Resistance Action Committee (IRAC).
Tips for Purchasing Insecticides
- Know the generic names of insecticides in brand name products.
- Develop a label file with cross reference system to access pest/site information for the products you use.
- Know the pH of the water where these pesticides are used.
- Know applicable regulations (restricted vs. general use products, FIFRA section 2ee, etc.).
- Store products in an organized fashion.
- Keep records of the cost of the finished spray material (dollars per acre, per ant mound, per 100 gallons, etc.).
- Purchase small quantities of products and target specific pests.
- Keep products fresh, particularly fire ant baits.
- Determine the proper application methods for products you buy, as well as the required equipment and adjuvants and the product's compatibility with other pesticides.
- Understand the product's mode of action, rate of kill and other technological characteristics.
Storing and Using Pesticides
Shelf life. Use fresh products whenever possible. Buy only what is needed for the current year and mark the purchase date on the container. The shelf life of pesticide products is influenced by the formulation, the container type and the storage conditions (temperature, humidity). As a rule, an unopened container stored at moderate temperature will remain effective for 2 to 5 years. Under poor storage conditions, the formulation and/or the active ingredient can deteriorate, separate or solidify. To prevent damage to equipment, mix a small amount of any suspect material in a jar first to see if it mixes properly. The only way to know if the active ingredients have been affected is to treat a pest infestation and monitor the results.
Alkaline water. The pH of water used as a diluent can affect the life of the active ingredient in solution. Many insecticides will degrade rapidly in alkaline water (pH greater than 7). Some ingredients, such as malathion and DyloxR, are particularly sensitive and degenerate within a few hours after being diluted. High temperatures increase the rate of degradation in alkaline water. Many product labels suggest proper pH ranges for water.
To prevent degradation of ingredients in a mixture:
- Mix the pesticide with water and spray immediately or within a few hours. Never allow pesticides to remain in solution overnight before spraying.
- Use an acidifier to adjust the ph of the water to neutral (ph = 7) or slightly acidic. Although vinegar is frequently recommended for lowering pH, commercially available buffers are better suited for this purpose.
Temperature effects. Temperature alone can affect pesticide effectiveness. Organophosphate insecticides work better at higher temperatures (except for DDVP which is best used at about 50 to 72 degrees F). Synthetic pyrethrum derivatives (sumithrin and resmethrin) are less effective at high temperatures. Many product labels suggest temperature ranges for making applications.
Look for the following symptoms which indicate that a pesticide may have deteriorated:
| Emulsifiable concentrate (EC) | No milky formation; insoluble sludge or layers in the mixture. |
| Wettable Powder (WP) | Product is lumping and some of the material won't go into suspension. |
| Dust | Excessive lumping |
| Granular | Excessive lumping |
| Aerosols | Obstruction in opening |
| Smoke | Difficult to light, lumping |
Pesticide Compatibility with Adjuvants
Many pesticides require no additives (adjuvants). But if there are concerns about pesticide degradation and coverage, an additive such as a buffer or a spreader/sticker may be needed. There are many types of adjuvants (tank additives), including emulsifiers, defoamers, drift retardants, spreaders, stickers, wetting agents, anti-caking agents, cuticle cutters, penetrants, buffers, translocation aids, nutrient buffers, thickeners, emulsion inverters, UV screens and evaporation inhibitors.
Adjuvants can be sorted into two categories:
- The activators improve the application and/or effectiveness of products (wetters, spreaders, stickers, emulsifiers, emulsifiable oils and plant penetrants or translocators)
- Some adjuvants have special purposes (drift retardants, defoamers, buffers, stabilizing agents and feeding stimulants, among others).
Surfactants are "surface acting agents" and are active ingredients in most adjuvants. Surfactants are either non-ionic, anionic (negatively charged) or cationic (positively charged). The pesticide's label will tell you whether the pesticide is compatible with the different kinds of surfactants. Surfactants work either as spreaders or stickers.
Spreaders break the surface tension of water and allow water-based sprays to spread out on a leaf rather than beading up. Soaps and detergents should not be used for this purpose. Soaps are alkaline and will break down many pesticides. Detergents containing sulfates and phosphates are highly reactive and may react with the spray mixture.
Stickers are used to stick solid pesticide particles to leaves, reduce pesticide volatilization and waterproof the pesticide. Many stickers also act as spreaders (alkylarylpolyethylenates). Most products that won't wash off with rain or irrigation contain latex (rubber), polyethylenes (plastic), resins (rosins), polymenthenes (resin-like compounds) or other long-chain polymers.
Buffers neutralize alkaline water, which normally breaks down insecticides through alkaline dehydrolysis. Phosphoric acid is the active ingredient in many buffering agents.
In Texas, it is legal to apply pesticides in any adjuvant as long as the percentage concentration of adjuvant in the spray is lower than the percentage concentration of water (carrier) in the tank. Tank mixes must contain at least 50 percent water carrier.
Consult the pesticide label before using an adjuvant. Many labels make specific reference to spreaders/stickers. If not, make a test application on a small number of plants to see if the mixture is beneficial. Determining whether pest control has been enhanced is more difficult. Be cautious. New, untested tank mixtures may cause phytotoxic reactions in plants.
There are so many products available that there are many possible combinations of pesticides and adjuvants. Few have been tested, however, so the grower must determine the usefulness of these products.
Phytotoxicity
Certain insecticides or spray mixtures cause plant damage called phytotoxic reaction. Pesticide labels usually mention sensitive plant species and cultivars. However, most plant listings on product labels are not binding and allow for these products to be used on other ornamental plants. The sensitivity of unlisted plants to the product or tank mixture is unknown.
Sensitive flowering periods and stressed plants. Plants usually are more sensitive to pesticides after they begin to bloom, and foliar sprays should be avoided or used with caution at that time. During bloom, the careful use of smokes or certain aerosol products may be preferable in the greenhouse.
Plants under water and/or temperature stress are also more prone to phytotoxic reactions. Avoid spraying when the weather is extremely hot and sunny. Spray in the mornings when possible, preferably between 6 and 10 a.m. When air or plant tissue temperature is about 90 degrees or higher, damage will likely occur. On bright, sunny days, leaf tissue temperature may be 5 to 15 degrees higher than that of the surrounding air, thus increasing the possibility of injury.
Pesticide formulations and application methods. Wettable powders are usually safer for plants than emulsifiable concentrates since they do not contain emulsifiers and solvents. The disadvantage of wettable powders is the objectionable residue left on the foliage by some products. Almost all aerosol and fogging formulations will cause phytotoxicity if applied at less than the recommended distance between nozzle and plant. A distance of 18 to 20 inches usually is recommended.
Tank mixtures. Mixtures of insecticides, miticides or fungicides may cause plant injury when the use of one of the materials alone would not. Pesticides should not be tank mixed unless this use appears on their labels, or unless the grower knows first-hand that the mix will not injure his crop.
Phytotoxicity testing. When using a product, tank mixture or application method for the first time, test it on a small group of plants and observe them for several days. With foliar applications the new growth is most likely to show phytotoxic damage. With soil drenches damaged root tissue may show up as plant stunting or slow decline, with the older, not younger,leaves damaged.
Symptoms of phytotoxic reactions. Plants react to pesticides in a number fo ways:
- Chlorosis - appears as spots or as tip, margin or leaf yellowing.
- Leaf distortion - appears as curling, crinkling or cupping of the leaf.
- Stunting - The entire plant is reduced in size or certain parts (fruit, flowers, roots) are smaller while the rest of the plant appears normal.
- Abnormal growth - Excessive growth on either certain parts (aerial roots, suckering) or the entire plant.
To avoid phytotoxicity, study the label and any brochures that are available concerning the particular pesticide to be used. Pay attention to dosage rates, application instructions and phytotoxicity information. Do not overdose. Use a clean sprayer after each use. Do not use sprayers in which herbicides have been used. Don't apply a pesticide to plants that are stressed. Never spray plants when they are in need of water, since wilted or dry plants are extremely sensitive to spray injury. Don't apply pesticides when the temperature is either very high or very low, or when the spray will not dry quickly. Under cool, humid conditions plants will remain wet, which increases the possibility of injury and disease. This is one of the reasons greenhouse plants are more likely to be damaged.
Proper Equipment Selection and Application
Pesticide use directions describe both site (greenhouse, interiorscape, etc.) and application method (foliar sprays, soil/medium treatments, aerosols and fumigants, etc.) for treating ornamental plants. The size of the planting and the sizes and structure of plants to be treated are also important considerations. The best application equipment for a particular situation is that which provides thorough coverage within a reasonable amount of time and effort.
High-volume foliar sprays. High-volume hydraulic applicators provide good coverage, particularly if care is taken to direct the nozzle(s) properly. Most pesticides are applied to the point of runoff to both the under- and upper-surfaces of foliage. However, some products (Bacillus thuringiensis, insect growth regulators and others) are applied to wet foliage only and instructions say to avoid runoff.
Coverage. When making applications, every effort should be made to determine if target surfaces are being reached. For less toxic, contact materials such as horticultural oils, insecticidal soaps, microbial insecticides and insect growth regulators, applying sprays directly to the pests or pest-infested surfaces is essential for good control. Coverage is relatively less important when using systemic pesticides. There are several dye products available that can be mixed with the sprayer contents to reveal areas where pesticides have been applied.
Soil-applied systemic insecticides. The use of soil-applied systemic insecticides before pest infestations occur is often referred to as a preventive treatment. Although these applications are convenient, they may or may not be justifiable either economically or environmentally. Making such applications unnecessarily can be a costly mistake. But if early pest outbreaks have occurred frequently in past production cycles, this approach can be justifiable.
It has been claimed that systemic insecticides are less harmful to natural enemies, since these organisms do not contact or directly ingest the pesticide. However, the period of protection offered by systemics varies. After application, landscape managers should continue to monitor for outbreaks of secondary pests and determine the length of the product's activity.
For more information, see Florida Wax Scale and Wood-boring Insects in Trees and Shrubs.
Rate Calculations
Conversion Equations
Liquid
1 level tablespoonful = 3 level teaspoonsful
1 fluid ounce = 2 tablespoonful = 29.57 milliliters
1 cup = 8 fluid ounces
1 pint = 2 cups = 16 fluid ounces
1 quart = 2 pints = 32 fluid ounces
1 gallon = 4 quarts = 128 fluid ounces
Weight
1 ounce = 28.3 grams
1 pound = 16 ounces = 454 grams
1 ton = 2,000 pounds
Dilution Tables
Wettable Powders
Number of ounces (oz) of wettable powder to use in small sprayers when amount per 100 gallons (gal) is known.
| 100 gal | 10 gal | 5 gal | 2 gal | 1 gal |
|---|---|---|---|---|
0.5 lb |
0.8 oz |
0.5 oz |
0.2 oz |
0.1 oz |
1.0 lb |
1.6 oz |
0.8 oz |
0.3 oz |
0.2 oz |
2.0 lb |
3.2 oz |
1.6 oz |
0.6 oz |
0.3 oz |
3.0 lb |
4.8 oz |
2.4 oz. |
1.0 oz |
0.5 oz. |
4.0 lb |
6.4 oz |
3.2 oz |
1.3 oz |
0.6 oz |
5.0 lb |
8.0 oz |
4.0 oz |
1.6 oz |
0.8 oz |
Emulsifiable Concentrates
Number of fluid ounces (fl oz) of emulsifiable concentrate (EC) to use in small sprayer when amount per 100 gallons (gal) is known.
| 100 gal | 10 gal | 5 gal | 2 gal | 1 gal |
|---|---|---|---|---|
1 pt |
1.6 fl. oz |
0.8 fl. oz |
0.3 fl. oz |
0.2 fl. oz |
1 qt. |
3.2 fl. oz |
1.6 fl. oz |
0.7 fl. oz |
0.3 fl. oz |
2 qts. |
6.4 fl. oz |
3.2 fl. oz |
1.3 fl. oz |
0.6 fl. oz |
1 gal |
12.8 fl oz |
6.4 fl oz |
2.6 fl oz |
1.3 fl oz |
Mist Blower
Quantity of emulsifiable concentrate (EC) needed to make a 25X concentrate.
| If amount per 100 gal for a high volume spray is: |
Use this amount in a mist blower: |
|||
25 gal |
10 gal |
2 gal |
1 gal |
|
1 pt |
6.25 pt |
2.50 pt |
8 fl oz |
4 fl oz |
1 qt |
6.25 pt |
5.00 pt |
1 pt |
8 fl oz |
2 qt |
3.13 gal |
5.00 qt |
1 qt |
1 pt |
1 gal |
6.25 gal |
2.50 gal |
2 qt |
1 qt |
Using Chemicals Safely
When used as recommended on their labels, pesticides are safe and effective. However, all pesticides are poisonous and, if misused, they may be hazardous to man and animals and may also contribute to the pollution of the environment.
Before using any pesticide, read the label in its entirety. Note any special precautions, such as the necessity of wearing special protective clothing when applying the chemical. Follow all safety precautions set forth on the label.
"An ounce of prevention is worth a pound of cure."
- Risk = toxicity x exposure. By simply reducing exposure, you reduce risk.
- Become familiar with the use of a pesticide before using it. Know its toxicity and the necessary precautions for its safe use.
- Where product labels specify wearing personal protection equipment (PPE), do so and keep all safety equipment such as face masks, respirators and protective clothing clean, on hand and in good working order.
- Mix pesticides in a well-ventilated area or outdoors. Avoid contact with skin, and do not breathe vapors.
- Much of the potential exposure to pesticides comes through your skin and hands. Wear rubber gloves when handling. Rinse the gloves before you take them off. Then wash your hands thoroughly. "Rubber Glove Zone" decals, booklets and videotapes are available from: NACA 1155 15th St., N.W., Washington, DC 20005.
- Where product labels specify, do not re-enter treated areas unprotected until the re-entry interval specified on the product label has passed. Post Do Not Enter signs.
- Cleanup is an important part of the application operation.
- Do not save used pesticide containers. Dispose of old containers properly.
- Handle clothing contaminated with pesticide with rubber gloves. Garments saturated with full strength liquid concentrate should be discarded. Launder clothing immediately after each day's use. Keep contaminated clothing separate from other garments. Pre-rinse contaminated clothing. Wash it separately in hot water. Use the full or normal water level and small loads. Use the recommended amount of heavy-duty liquid detergent with oil-removing abilities. Line dry the garments. Run an empty load after washing contaminated clothing and clean the washing machine thoroughly. Use disposable protective clothing and equipment whenever possible when handling pesticides.
Summary of pesticide regulations.
See Agricultural and Environmental Safety.
Avoiding groundwater contamination
Many of the agricultural chemicals identified in contaminated groundwater have been herbicides. Growers must take precautions to minimize the leaching of chemicals. Precision application to the root zone and controlled irrigation for as long as possible after treatment should reduce leaching.Pesticides must be stored away from water supplies and wells. If available, use returnable, recyclable containers. Install a back siphon or back-flow device on the water line to keep fertilizer or pesticide from siphoning back down the pipe used to bring water from the aquifer.
In addition, do everything possible to eliminate runoff which can carry fertilizers and pesticides into groundwater.
Selected references for pest control recommendations
Hamman, P. J. 1984. "House and Landscape Pests", B-1373. Texas Agricultural Extension Service. Dept. of Agric. Communications, Reed McDonald Building, Texas A&M University, College Station, Texas 77843.
Lindquist, R. K. 1987. Insect and mite control chart-1&2, Ohio Florist's Assn. Bull. #651. Sponsored by the Florist's Insurance Companies, 500 St. Louis St., Edwardsville, IL 62025.
Miller, R. L. and D. G. Nielsen. 1985. "Insect and mite control on woody orna- mentals". Bull. 504. Cooperative Extension Service, Ohio State University, Extension Publications Office, 2120 Fyffe Road, Columbus, OH. 43210.
Miller, R. L. and D. G. Nielsen. 1985. "Insect control on Christmas trees", L-257., Cooperative Extension Service, Ohio State University, Extension Publications Office, 2120 Fyffe Rd, columbus, OH. 43210.
Mother Earth News (ed.). 1989. The Healthy Garden Handbook. Simon and Shuster Inc., Simon & Shuster Bldg., Rockerfellar Center, 1230 Avenue of the Americas, New York, New York, 10020. 192 pp..
Powell, C. C. and R. K. Lindquist. 1984. "Pest and disease control on indoor plants". Bull. 11. Cooperative Extension Service Ohio State University, Extension Publications Office, 2120 Fyffe Road, Columbus, OH. 43210.
Short, D. E. 1983. Plant Protection Pointer: "Phytotoxicity of Insecticide and Miticidesto foliage and woody ornamental plants". Extension Entomology Report #57. Institute of food and Agric. Sciences, University of Florida, Gainesville, FL. 32611.
Thompson, W. T. 1983. Tree, Turf and Ornamental Pesticide Guide. Thomas Publications, P. O. Box 9335, Fresno, CA. 93791.
The society of American Florists publishes a list of pesticide brand names. For information on obtaining this list write Valarie Kurylo, Society of American Florists, 1601 Duke St., Alexandria, VA 22314.
