Chapter IX: Chemical Application and Safety

Jerral D. Johnson and Charles Cole

The use of pesticides aids in vegetable production improvement. Despite the fears and real problems pesticides can create, these crop protection chemicals improve environmental quality for man, animals and plants.

More than 50,000 destructive plant diseases exist today. Over 10,000 species of insects are considered as pests. A composite list of over 1,775 weeds has been identified by the Weed Science Society of America. With pests such as plant diseases, insects, and weeds decreasing the already inadequate food supply in the world, a need for some means of controlling pests in order to improve the quality and quantity of vegetables produced today is required.

Manmade chemicals are often used as the front line of defense against destructive plant diseases, insects, and weeds. When properly used, they can minimize agricultural losses and pest competition. Knowledge of the pest to control, availability, chemical characteristics and capabilities, application techniques as well as safety concerns are all an integral part of the planning process of a conscientious producer.

Types of Pesticides

Pesticides commonly used around vegetables include chemicals to control diseases, insects, and weeds, control growth and modify harvest. These chemicals come in different formulations.


Pesticide formulations include emulsifiable concentrates, wettable powders, flowables, dry flowable granules, soluble powders, granules, dusts, baits and aerosols.

Emulsifiable concentrates (EC): consists of the pesticide and emulsifying agent in an organic solvent. The solvent may be one that evaporates with the water after spraying, leaving a pesticide deposit on the plant or a nonvolatile solvent which covers the treated surface with a pesticide and oil solution. Emulsifying agents permit the organic product to disperse in water forming an emulsion; a milky appearing mixture is formed when water is added. Invert emulsions differ from emulsifiable concentrates because a water solution is dispersed in oil forming a thick mayonnaise-like mixture.

Dusts (D): a pesticide and carrier or diluent, usually talc, clay, diatomaceous earth, etc. Sometimes mixtures of carriers are used to obtain the desired bulk density. They are usually not mixed with water.

Wettable powders (WP): are similar to dust formulations except a wetting agent and sometimes a spreader-sticker are added. The wetting agent makes it possible to disperse or suspend the wettable powder in water for use as a spray. Constant agitation keeps the mixture in solution.

Soluble powders (SP): are similar to wettable powders except that the particles completely dissolve in water rather than going into suspension.

Flowables (F): are concentrates of a liquid or solid suspended in a liquid. Most flowables contain a finely ground pesticide powder suspended in water.

Dispersible granules or dry flowables (DG) (DF): were developed to reduce applicator exposure during measuring. There is little or no dust. The pesticide consists of small beads which disperse into a suspension when added to water.

Granules (G): contain the pesticide and a carrier or diluent, such as attaclay, vermiculite, or some similar inert material mechanically formed into pellets or granule, reducing the amount of dust or “fines” formed upon handling. Granular formulations are applied directly to the soil or planting medium and washed in or incorporated in the soil.

Baits: are available in various types and consist of the pesticide and a material that the pests will readily eat. Baits may contain sugar, molasses, apple pomace and similar food products.

Aerosols (A): liquids containing an active ingredient and a solvent. They are applied as a fog or mist in closed structures or greenhouses. Most are available in pressurized containers and contain a propellant. They can cause plant damage if not properly used.


Adjuvants are materials added to pesticides to: improve their efficacy by extending their effectiveness, increase their retention on leaves, improve coverage, and buffer spray solution to reduce pesticide decomposition or reduce spray drift. Wetting agents, emulsifiers, spreaders, spreader-stickers, penetrants, drift reduction agents, thickeners, buffers or compatibility agents are adjuvants often used when spraying vegetables.

  • Buffering agents adjust the pH of alkaline (high pH) water. The pH of some water can cause some pesticides to fall out of solution or become inactivated.
  • Compatibility agents allow mixing of chemicals together in a spray mix by helping to improve the stability, solubility and uniformity of a mixture. These materials aid the mixing of two pesticides or pesticides and fertilizers.
  • Crop oil or crop oil concentrates are composed of a petroleum or vegetable oil, and may also contain a surfactant and other agents.
  • Drift control agents reduce the drift of pesticides from their intended target by increasing the percentage of large droplets discharged from the spray nozzle.

Ingredients in Pesticides

Formulations are combinations of two or more of the following ingredients:

  • Active ingredients: The active ingredient is the chemical which is toxic to the target pest. It is designated as percent of the concentrate total.
  • Solvent: The solvent is a compound used to dissolve the active ingredient, which may be a solid. Some common solvents are acetone, kerosene, varsol, and hexane.
  • Emulsifier: An emulsifier is a soap or chemical which, when used, will allow an oil and water to mix.
  • Diluent: Compounds which dilute the total ingredients to a desired concentration in the pesticide product. They may be inert ingredients such as powdered rock or clay.
  • Synergist: A synergist is a chemical which, when mixed with the pesticide product, may increase the pesticides activity.
  • Spreader: sticker

Disease Control Materials

Disease control products are pesticides used to prevent or control pathogens which cause plant diseases. The three groups of disease control pesticides, based on pathogens controlled, are fungicides, bactericides and nematicides.


Fungicides are applied to the soil to control root infecting pathogens. They are sprayed onto the foliage and fruit and also used as post harvest dips to prevent storage or shipping disease losses. Fungicides work in two different ways:

  • Protective fungicides are applied to the plant before infection.
  • Eradicant fungicides control fungi which are already established in the host plant.

Early fungicides were protective in their mode of action. Benomyl was one of the first widely used fungicides that had limited systemic activity. Many new fungicides are systemic. Metalaxyl seed treatments effectively control downy mildew of sweet corn and seed decay caused by Pythium fungus.

Application Time: Fungicides are applied on 10 to 14 day intervals. During periods of favorable weather for fungus development, the shorter interval should be used. Although some fungicides have systemic activity, all are most effective if applied before the host plant is infected.


Bactericides are products that control bacterial diseases. They are applied as foliar sprays or used as post harvest treatments to prevent disease losses during harvest or storage. The basic types of bactericides are:

  • Primary bactericides: Copper containing pesticides comprise the primary bactericides.
  • Antibiotics are used on tomatoes and peppers to control bacterial diseases. Streptomycin sulfate is the active ingredient.

Copper containing pesticides are protective and must be applied before the host plant is exposed to pathogenic bacteria. Streptomycin sulfate is systemic, but should be used as a preventive treatment. Normally bactericides are applied on a 10 to 14 day interval. Use the shorter interval if climate conditions favor rapid disease development.


Nematicides are products that control nematodes in the soil. These may be liquid and injected into the soil, sprayed onto the soil surface, applied as granules and soil incorporated or sprayed directly onto the plant foliage. Examples of the basic types of nematicides are:

  • Organophosphates which kill nematodes when they come in contact with the lethal dose of the pesticide. They are applied as row or broadcast treatments for the control of nematodes.
  • Fumigants are pesticides that produce a lethal gas toxic to nematodes. They are used to control nematodes in plant beds and in field soils. Fumigants also control weed seeds, soil fungi, and many soil insects.
  • Oxamyl is a systemic pesticide. It is used to control nematodes on several vegetable crops.

Application Time: Fumigant type materials must be applied 2 to 3 weeks prior to planting to allow for phytotoxic pesticide levels to escape from the soil. Organophosphate materials can be applied prior or at planting. Oxamyl can be applied at planting or as a post plant treatment.


Chemical nature and mode of action are two methods of categorizing insect control products. A combination of the two methods can be most accurately used to describe an insecticide.

Chemical Nature:

  • Plant derived organic insecticides come from plant parts such as leaves or roots. This group includes rotenone, pyrethrins, strychnine, and nicotine. These insecticides can be used against several pests.
  • Living microorganisms such as viruses, bacteria, and fungi are effective as insecticides and are selective in the organisms which they kill. Some examples of this type are Bacillus thuringiensis and the polyhedrosis virus used to control certain chewing larvae.
  • Inorganic insecticides are those made from minerals. They include sulfur, arsenic, boron, and diatomaceous earth.
  • Synthetic organic insecticides are manmade compounds. They contain carbon, hydrogen, and other elements such as nitrogen, phosphorus, or chlorine. Examples of synthetic organic insecticides include Malathion, Diazinon, Orthene, and Sevin.

Chemical activity:

  • Contact poisons kill insects on contact.
  • Stomach poisons kill the insect after they are ingested by the pest.
  • Systemics are taken in by the plant and the plant juices contain the poison which kills the insect as it feeds.

Application Time: Insecticides are applied preplant, at planting and during the season when the insect populations are high enough to require treatment. Treatments should be made only after scouting the field and determining that an insect population is sufficiently high to cause economic crop damage.


Herbicides are products which control weeds. They are categorized by selectivity and mode of action.


  • Nonselective herbicides are sometimes called soil sterilants. They are often used around buildings or fences to control undesirable weeds or brush. Some nonselective herbicides are extremely toxic to trees and other nontarget plants which might be growing in the vicinity of the treatment. Many of these products are persistent and will remain in the soil for several years.
  • Selective herbicides are used in and around vegetables. They are divided into preplant, preemergent and postemergent herbicides. Preplant herbicides may be applied before seeding the crop, some of which require incorporation. Preemergent herbicides may be applied before seeding the crop, preemergent of the crop or preemergent of the weeds and the crop. Postemergent herbicides are applied following emergence of the crop or weeds or both. Selectivity of some herbicides is accomplished by placement rather than chemical selectivity.

Mode of Action:
Contact herbicides kill the plant tissue that it contacts.
Systemic or translocated herbicides are moved within the plant away from the site of application and may affect the plant by interfering with normal growth.

Growth regulators or harvest aid materials control or modify plant growth, stimulate formation of female flowers or induce uniform ripening.

Pesticide Application

The success of a pesticide application depends on the pesticide and proper application. Improperly applied pesticides can result in ineffective control, plant injury or excessive pesticide residues. Maximum coverage of the target area is essential to the control of plant pests. Spray coverage is depended upon; tractor speed, rate of diluent, and droplet size. Time spent preparing and calibrating the application equipment is important. Pesticides are a major part of most crop budgets. Every effort should be made to insure that applications are correct and safe.

Sprayer Types:

Hand held portable sprayers come in a variety of sizes. However, calibrating these type sprayers can be difficult because pressure and rate of application are difficult to control. Most of the handheld sprayers are constructed of plastic or stainless steel.

Backpack mist blower sprayers use a small motor to generate wind which acts as a carrier for the pesticide solution. This type of sprayer is excellent for applying fungicides and insecticides to small acreage. The calibration is difficult due to variations in speed and flow rate. Some of the newer sprayers also have a small motor to maintain pressure and agitation.

Boom type sprayers use pumps to develop a constant pressure and a static boom equipped with atomizers that break up and direct the spray solution. Most sprayers deliver 5 to 100 gallons of water per acre. For vine crops such as watermelons, cucumbers and cantaloupes, rates may range up to 100 gallons per acre on mature plants. Sprayers may be mounted on a tractor chassis or self propelled. Tractor PTO, hydraulics, or independent power source operates the pump. Basic sprayer components consist of tank, pump, pressure gauge, regulator, agitator, hoses, valves, fittings and nozzles. Nozzles are mounted on the boom which is suspended over the row. Number and size of nozzles depends on pump capacity and crop. Table IX-1 summarizes sprayer types and their uses.

Table IX-1. Summary of Sprayer Types

Type Size Tank Pressure Speed Cost Use
Small Sprayers
Handheld 1 – 3 gal variable1 variable2 $15 – $100 Spot, small acreage
Backpack 3 – 5 gal variable variable $90 – $150 Spot, small acreage
Backpack 5 gal constant3 variable $400 Spot, small acreage
Backpack (mist blower) 2 – 3 gal NA4 variable $400 – $600 Spot, small-medium size acreage
Handheld controlled
Droplet sprayer 2 – 5 pt NA variable $200 – $300 Spot, small acreage
Large Sprayer
Boom sprayer (tractor mounted) 25 – 300 gal constant constant $200 – $2,000 Small-large acreage

1 Not able to hold constant pressure
2 Speed varies with walking speed
3 Pressure can be set and maintained
4 Not available

Row Crop Air Sprayers use a blower which generates air that acts as part of the carrier for the pesticide. The spray solution is blown across several rows. Initially sprayers used a two way discharge. Cost of equipment and inability to spray during periods of moderate to high winds are two limiting aspects to the use of this sprayer type. Swath width must not exceed the capabilities of the sprayer and existing weather conditions.

Aerial Application involves the use of fixed wing and helicopters for the application of pesticides. Size of fields and their location often restricts the efficient use of aerial application.

Spray Equipment


Sprayer tanks should be rust resistant, preferably fiberglass, polypropylene, or stainless steel. Filler openings should be wide enough for ease in filling. A splash proof filler should be in the tank to prevent pesticides from splashing onto people during filling or while spraying. Each tank should be equipped with a drain. Intake on the suction line should be at the bottom of the tank. Mechanical or return agitation should be used to keep pesticides in solution or suspension.


There are several types of pumps capable of spraying pesticides. Roller, gear, centrifugal and piston pumps are most often used. Sprayer operation and pesticide formulations influence pump selection. Piston, roller and diaphragm pumps are positive displacement; therefore, the flow rate is determined by pump speed, not pressure. Centrifugal pumps are a nonpositive displacement type and flow rate is influenced by pressure.

  • Gear pumps: can be used to spray emulsifiable concentrates. Wettable powders will cause excessive wear and shorten pump life.
  • Roller pumps: are economical, light to moderate duty pumps with limited life expectancy. Certain pesticides and wettable powders will significantly shorten the life of a roller pump.
  • Centrifugal pumps: operate at over 3,000 revolutions per minute. They are high volume, low pressure pumps.
  • Piston pumps: are often the most expensive. They operate at high and low pressure. Volume ranges from 2 to 50 gallons per minute.

Piston and centrifugal pumps are better for handling abrasive materials such as wettable powders. Proper agitation is important in all spray mixes but is critical for wettable powders.

Before buying a pump, the desired capacity should be determined using the following formula:

gallons per mile = (miles per hour times swath width (in feet) times gallons per acre) divided by 495

Example: A two row sprayer with an 8 foot boom and the maximum rate to be applied is 35 gallons per acre. The desired speed is 3 miles per hour.

(3 times 8 times 35) divided by 495 = 1.7 gallons per mile

This is the delivery rate for the pump. Adequate return agitation requires a pump capacity about 1/3 above the calculated rate.

Pressure Regulators

Pressure regulators adjust the solution flow. When the regulator is open, a constant flow is directed to the nozzles, and the overflow returns to the tank. When closed, all flow is diverted to the tank.

Pressure Gauges

Show the line pressure at the location where the gauge is positioned. The gauge should be located between the pressure regulator and nozzles. The best location for the gauge is on the boom. This gives the most accurate pressure reading at the nozzle. However, most producers find it more convenient to place the gauge near the regulator and operator. This makes it easier to adjust pressure. However, there will be some drop in pressure because of flow restriction from the hoses. A pressure gauge is necessary to accurately calibrate a sprayer.


Screens positioned to protect pump and nozzle tips are called strainers. Different size strainers can be purchased. A screen with large openings may not adequately screen out particles which can damage a pump or clog nozzles. If the openings are too small they become clogged and restrict flow. Strainers located in the nozzle should have a diameter slightly smaller than the nozzle orifice. A slotted strainer is suggested when applying wettable powders.


Nozzles have three functions in the spray operation. They control the flow rate, droplet atomization and droplet distribution. They come in several different types, and each has a specific purpose in pesticide application.

Hollow cone nozzles: concentrates most of the spray solution at the outer edge of a conical pattern. They operate at high pressure and produce small droplets which effectively penetrate plant canopies. Hollow cone nozzles are often used with foliar nutrients, fungicides and insecticides. They operate in a pressure range between 60 to 100 psi.

Flat fan spray nozzles: produce narrow elliptical spray patterns. There is an uneven spray deposit in the pattern. A greater proportion of the spray solution is deposited near the center of the pattern and a lesser amount is deposited at the outer margin. To get a uniform spray application, patterns must overlap. Broadcast herbicides, soil fungicides and soil insecticides are applied using flat fan nozzles. A pressure of 20 to 40 psi is required for optimum utilization. Even flat fan spray nozzles produce an elliptical pattern with even deposition of the material across the pattern. Banded pesticides are applied with flat even fan nozzles. Fan angles are 40 degrees, 80 degrees and 95 degrees. Pressure should be 20 to 40 psi and never over 40 psi. Table IX-2 gives the nozzle height required for effective spray application with fan nozzles.

Flooding flat fans/nozzles: are used to apply preemergence and post emergence herbicides. They deposit a fan pattern. Droplets are large. They should operate at a pressure of 5 to 20 psi.

Table IX-2. Nozzle height for flat fan nozzles

Nozzle Height (inches)
Spray Angle 20″ Spacing 30″ Spacing
65 21 – 23 32 – 34
80 17 – 19 24 – 26
110 10 – 12 13 – 15


Hoses used on sprayers should be oil resistant and have a test pressure twice the operating pressure. A two ply hose should be used on the suction side of the pump. This will prevent collapsing. Hoses should be of sufficient size to prevent excessive pressure drop or loss. Table IX-3 lists the hose sizes and flow rates.

Table IX-3. Normal Hose Flow Rates

Hose Size in inches 3/8″ 1/2″ 5/8″ 3/4″ 1″ 1 1/4″
Max. Flow (gpm) 2 4 8 12 20 40

Number of Nozzles per Row

The number of nozzles per row depends on the crop being sprayed and plant size. Small, flat growing plants normally require one or two nozzles over the top. Upright growing plants such as peppers, tomatoes, and Irish potatoes require one or two nozzles over the top of the crop and a drop on either side. Drops improve coverage on the lower half of the plant.

Table IX-4 lists various materials used in the manufacture of nozzles. Most producers use brass or nylon nozzles because of availability and cost. Nozzles should be checked regularly to make sure tips are free of debris, and the orifice is not worn. Clogged tips should never be cleaned with a knife; use a soft toothbrush. When the nozzles are worn or damaged, it is time to replace them. If an herbicide treatment cost $50 an acre, a 10% overspray on a 100 acre farm costs $500. Always wash your sprayer after each use when applying herbicides with water and ammonia or bleach (but not both). Water is sufficient to wash out the sprayer if insecticides, fungicides were applied.

Table IX-4. Materials Used in the Manufacture of Nozzles

Material Corrosive Abrasive Cost
Brass Mod. Resistant Susceptible Inexpensive
Nylon Resistant Susceptible Inexpensive
Stainless Steel Resistant Resistant Expensive
Hardened Tungsten Resistant Resistant Very Expensive
Ceramic Resistant Resistant Very Expensive

Sprayer Calibration

No matter how effective or safe a pesticide is, its performance is dependent on applying the proper rate. Accurate calibration of spray equipment is an important part of pest control. Poor calibration accounts for about 90% of weed control failures.

Applications made using sprayers that are not properly calibrated can result in plant injury, ineffective control, excessive pesticide costs and possible residue problems. The following steps should be followed before calibrating any sprayer.

  • Rinse and clean the tank with clean water.
  • Remove and clean all nozzles and screens.
  • Start sprayer and flush hoses and boom with clean water.
  • Replace screens and nozzles. Make sure all nozzles and screens are of the correct size and type.
  • Check hoses and connections for leaks.
  • Adjust the pressure regulator to the desired pressure with tractor running at desired rpm.
  • Operate the sprayer and check the discharge rate of all tips. Any nozzle which is off 10% from the average rate should be replaced.

Backpack Sprayer

Most backpack sprayers can be used to apply pesticides. Liquid materials are easier to use than wettable powders since backpacks do not have agitation. The calibration of a backpack sprayer is similar to the calibration of a tractor mounted boom rig.

The person carrying the backpack must walk at a uniform speed. Walking speed will vary depending on the soil surface, and how level the bed being sprayed. Calibrate the sprayer under field conditions.

The spray wand must be held in a reasonably fixed position above the soil or plant as the applicator walks.

Steps in Calibrating:

  1. Determine the calibration distance from Table IX-5, based on nozzle spacing if a boom has 2 or more tips or the width of the spray pattern if a single spray tip is used. For example, with a 20″ tip spacing or spray pattern width, measure a distance of 204 ft.
    Selecting Spray Tips: Backpack sprayers usually come equipped with plastic spray tips that are adequate for most pesticides, but it is better to switch to brass or stainless steel tips for accuracy and longevity.
  2. With the sprayer strapped on and at least half full of water, record the number of seconds required to walk the measured distance at a uniform, comfortable speed (2 to 3 mph). For example, at 3 mph it requires 46 seconds to walk 204 ft.
  3. Pump up the sprayer to the desired pressure, usually 15 to 30 psi. Pressure regulators and a gauge to preset and read the pressure are accessories available for most backpack sprayers. Maintain the desired pressure. Collect the spray from one tip for the length of time required to walk the calibrated distance. If a boom has multiple tips, repeat this on other tips to check for spray uniformity. For example, continuing with the above example and using 8003 tips at 20 psi, in 46 seconds each tip should deliver almost 21 fluid ounces of spray.
  4. The number of ounces of spray collected will equal gallons of solution that you apply per acre. For example, 21 ounces of water = 21 gallons per acre.

Table IX-5. Spray calibration distances for different tip spacing (a boom with 2 or more tips) or spray pattern widths (a single tip)

Nozzle Spacing (inches) Calibration Distance (feet)
28 146
24 170
20 204
18 227
16 255
14 292
12 340
10 408

Tractor Drawn Sprayer

  1. Use chart for distance to drive in field. Use nozzle spacing for booms. For directed and band rigs use the row spacing (Table IX-6). Mark off this distance in the field you will be spraying.
  2. Attach all equipment to the tractor that will be used during spraying. Determine the throttle setting and gear that will be used during spraying. Attain operating speed (usually 3 to 5 mph) before passing the starting mark, and note the time (in seconds) required to drive from the starting to finishing mark of the distance measured in step 1. Repeat to insure accuracy.
  3. Catch the nozzle discharge for the noted time in step 2 in a container graduated in ounces. If you are using a broadcast boom with evenly spaced nozzles, catch the output from one nozzle per row. If a directed spray is to be applied, catch the spray from each nozzle and combine the total number of ounces.
  4. The total nozzle output in ounces from one nozzle (or group of nozzles if more than one nozzle per row is used) is equal to gallons per acre applied.
  5. Check each of the nozzles to ensure they are discharging the same amount of liquid. Repeat steps 3 and 4 and replace any nozzles that vary more than 10%. The spray volume can be increased by decreasing tractor speed, increasing sprayer pressure, decreasing nozzle spacing or increasing nozzle size.
  6. Repeat for each nozzle to assure uniform distribution.

Table IX-6. Required Distance to Travel at Different Nozzle Spacing

Spacing (in) Row Width or
Nozzle Distance (ft)
Spacing (in) Row Width or
Nozzle Distance (ft)
40 102 26 157
38 107 24 170
36 113 22 185
34 120 20 204
32 127 18 227
30 136 16 255
28 146 14 291

Calibration Examples

Situation 1 – Broadcast application

You want to apply Treflan 4EC at 1 pint per acre, preplant incorporated, and prior to transplanting peppers. You have a 200 gallon tank; flat fan nozzles spaced 20 inches apart, and are using a disk for incorporation.

  • Measure a distance of 204 feet (based on the 20 inch nozzle spacing).
  • Choose a gear and throttle setting, and with a disk engaged, travel 204 feet (assume it took 35 seconds).
  • Set the spray pressure and catch one nozzle’s output for 35 seconds (the time required to travel 204 feet).
  • If you catch 20 ounces of spray from one nozzle in 35 seconds, the spray volume is 20 gallons per acre.
  • Recheck each nozzle’s output to be sure they do not vary more than 10% (if the average spray volume is 20 ounces, then a nozzle should not deliver more than 21 ounces or less than 19 ounces).

How many acres can you spray from one 200 gallon tank if the spray volume is 20 gallons per acre?

200 gallons per tank divided by 20 gallons per acre volume  = 10 acres sprayed per tank refill

How much Treflan 4EC should you add to the tank if you want to apply it at 1 pint per acre?

(10 acres covered per tank refill x 1 pt per acre wanted) divided by (1 gallon + 1 quart) of Treflan 4EC per tank  = 10 pints

Situation 2 – Banded spray

You want to apply Prefar on a 16 inch band preplant incorporated at 5 quarts per acre for watermelons planted on 80 inch rows. You have a 500 gallon tank, even tip nozzles spaced 80 inches apart and a rototiller for incorporation.

  • Measure a distance of 51 feet based on the 80 inch nozzle spacing.
  • Choose a gear and throttle setting and note the time required to travel 51 feet (assume it took 12 seconds).
  • Since it is difficult to accurately measure the spray output in only 12 seconds, catch the spray nozzle output from one nozzle for 24 seconds. If you collect 22 ounces in 24 seconds, divide it by 2, giving you a spray volume of 11 gallons per acre.
  • Recheck each nozzle’s output as previously described.

How many acres can you spray from one 500 gallon tankful of spray?

500 gallons per tank  divided by 11 gallons per acre spray volume = 45.5 acres sprayed per tank refilled

How much Prefar should I add to the tank if I want to apply 5 quarts per acre?

(16 inch band times 5 quarts of water) divided by 80 inch rows = 1 quart per acre

1 quart per acre times 45.5 acres per tankful= 45.5 quarts
45.5 quarts = 11.4 gallons

Situation 3 – Post-directed banded spray

You want to apply Sencor 4 at 1½ pints per acre on a 14 inch band to tomatoes on 40 inch rows. The tomatoes were transplanted 2 1/2 weeks ago, and your directed spray rig has two cultivator mounted, flat fan nozzles per row (off-center tips are also good) and a 300 gallon tank.

  • Measure a distance of 102 feet (based on 40 inch rows)
  • Set the speed with a cultivator down.
  • Assuming it took 25 seconds to travel 102 feet, catch the total discharge at a set pressure from both nozzles for 25 seconds. Let’s assume 10 ounces per tip, for a total of 20 oz caught in 25 seconds. The spray volume is 20 gallons per acre.
  • Check all the other nozzles for each row for uniformity.

How many acres can you spray from one 300 gallon tank if the spray volume is 20 gallons per acre?

300 gallon tank  divided by 20 gallon per acre = 15 acres per refill

How much Sencor 4 should I add to the tank if I want 1½ pints per acre?

(14 inch band width x 1½ pints per acre) divided by 40 inch row spacing = 0.525 pint per acre

Since we already know a tankful will spray 15 acres:

0.525 pints per acre times 15 acres = 7.8 pints per tankful

For further information refer to publication L-1839 Mixing Instructions for Liquid Herbicides. As an aid to proper calibration, common conversions are given in Table IX-7.

Table IX-7. Conversion Table

1 tablespoon = 3 teaspoons = 0.5 ounces
1 oz. = 2 tablespoons
1 cup = 1/2 pint = 16 tablespoons = 8 ounces
1 pint = 2 cups = 32 tablespoons = 16 ounces = 1 lb.
1 gallon = 16 cups = 8 pints = 4 quarts = 8.4 pound of water
1 cu. feet = 7.48 gallons o= 62.4 pounds
1 acre = 43,560 sq. feet
1 mph = 88 feet/minute

Cleaning and Care of Sprayers

More pumps are ruined by improper maintenance than are worn out. Pump wear and deterioration are brought about by ordinary use, but they are also accelerated by misuse. Following are suggestions that will help minimize labor problems and prolong the useful life of the pump and sprayer.

  • Put clean chemicals and solutions into the sprayer, and use clean water. A small amount of the silt or sand particles can rapidly wear pumps and other parts of the sprayer system.
  • Use chemicals that the sprayer and pump were designed to use. For example, liquid fertilizers are corrosive to copper, bronze, ordinary steel and galvanized surfaces. If the pump is made from one of these materials, it may be completely ruined by just one application of liquid fertilizer. Stainless steel is not adversely affected by liquid fertilizers. Use pumps made from this substance for applying these types of fertilizers.
  • Before using a new sprayer, dismantle it, clean the screen, nozzles, etc., of all metal chips and other foreign solid materials.
  • Flush the spray system with clean water after each day of spraying.
  • Inspect all strainers, screen and nozzle tips after each day of spraying. If these need cleaning, remove the accumulation by soaking and brushing. Never use a metal object for cleaning. Hard instruments scraping on a fine mesh screen can enlarge openings. This is also true of nozzle tip orifices.
  • Some chemicals such as 2,4-D leave residues that are difficult to remove. When spraying susceptible crops, do not use spray equipment that has been used for 2,4-D and other herbicides.
  • Clean the sprayer thoroughly after each use or when chemicals are changed. Many chemicals cause rapid corrosion of the metal in the sprayer. Remove and flush immediately after use. Sometimes a chemical residue will react with succeeding chemicals, causing a loss of effectiveness. Some of these risks may be eliminated by following this cleaning procedure.
  • Flush the sprayer with a tank of clean water.
  • Remove all strainers, screens and nozzles and wash them in kerosene with a soft appropriate size brush.
  • Mix a medium size box of wash day detergent and 30 gallons of water in the sprayer tank. Circulate this mixture through the bypass pressure regulator and jet agitator for 30 minutes. Drain the mixture.
  • Replace the screens and nozzles.
  • Fill the tank one-half full with one part household ammonia to 49 parts of water. Circulate this mixture through the pump and bypass, allowing a small amount to leak out through the nozzles. Let the solution stay in the sprayer overnight and run it out through the nozzles.
  • Flush with clean water. Remove the nozzles.


Chemigation is the application of pesticides through an irrigation system. Fungicides, nematicides, insecticides, herbicides, and fertilizers can be applied with this type of system.

Advantages to chemigation:

  • Uniformity of application
  • Ease of chemical incorporation
  • Reduction of soil compaction
  • Less mechanical damage to crop
  • Reduced hazard to operator
  • Economical application

Disadvantages to chemigation:

  • Additional equipment requirement
  • Safety considerations to groundwater, humans and environment
  • Maintenance of equipment

Soil Applied Pesticides

Broadcast applications: are applied to the soil surface and then incorporated. Use a disk or tiller to lightly incorporate materials into the soil. A boom type sprayer can be used to apply materials in front of the incorporator. Low pressure and flat fan nozzles reduce drift.

Banded applications: are made over the row or bed before planting or after seeding. Treated bands vary in width depending on the material applied. Any type of equipment can be used that will mix the top one to two inches of soil and not destroy the bed. The crop should be planted or transplanted without farther removal of surface soil. Some pesticides can be applied after planting and then incorporated. A basket or roller incorporator can be used. These do not distribute the seed. Sprinkle irrigation is sufficient to incorporate some pesticides. A back pack sprayer can be used to apply this type of treatment on small fields. When using a back pack sprayer the operator should always be the same and should take frequent rest stops. This is to insure that the application rate remains constant.

In-furrow applications: are the applications of pesticides directly in the seed furrow. Materials are applied with an even flat fan nozzle, low rate of water and low pressure.

Granular Applications

Granules can be applied as broadcast, banded or in-furrow treatments. The application of these products, like sprays, must be accurately calibrated.

Nematicide Injections

Some nematicides are injected into the soil. There are pump applicators which release the material into the soil under constant pressure. Other units use gravity flow. Orifices control the flow rates for both gravity and positive pressure applicators. Place the materials in the beds at a depth of 6 to 8 inches. It is best to use two shanks per row with their outlets 8 to 12 inches apart. Seal the bed immediately to prevent the material from escaping. The beds can be sealed with rolling cultivators, bed shapers or rollers. Most fumigant nematicides will move 6 inches in all directions from the injection site. An exception to this would be in soils that have a plow pan, water saturated soils or the soils have a high level of organic matter. If two shanks are placed 12 inches apart, the treated band will be 24 inches. Granular nematicides must be incorporated. Depth of incorporation varies with pests and pesticide.

Pesticide Safety

When it is necessary to use pesticides, use them wisely and safely. The following tips will help you make better use of pesticides:

  • Inspect plants and monitor disease and insect numbers and activity on a regular basis. Pay particular attention to underside of leaves where insects and their eggs frequently occur. The older plant foliage will often be the first to show disease symptoms. If treatments are applied when an infestation first starts, plant pests can be maintained at lower levels much more easily and with smaller amounts of chemicals.
  • When applying pesticides to plants, treat all plant surfaces unless otherwise stated on the product’s label. Do not apply pesticides to wilted plants or during the hottest part of the day. Apply dusts only when the wind is calm and plants are dry. Sprays should be applied when the wind is no more than 5 to 10 mph. Retreatment may be necessary after a rain if the spray did not dry thoroughly.
  • Apply pesticides only at recommended dosages; increased amounts can be dangerous, cause plant damage and leave harmful residues without improving control.
  • The length of effective control of pesticides varies widely. The toxic properties longevity of a chemical varies with product formulation, water pH, soil pH, and environmental conditions. Temperature, humidity, wind and sunlight affect insecticides. The greater the extremes, the sooner the pesticides are detoxified.
  • The interval required by the Environmental Protection Agency between treating and harvesting edible crops varies with the pesticide and crop. This information is on the pesticide label to ensure that any residues will be within established tolerances at harvest time.
  • Always read and follow mixing and application instructions on the label for safe and effective control.
  • Select the product that will effectively, economically, and safely control the target pests safely. Labels are a source of information about the product and its handling. Read and carefully follow the label.

All pesticides are classified according to their hazard potential to humans, animals and the environment. Classification is not based on activity against plant pests. The three signal words include:

  • DANGER tells you the product has the highest hazard potential. This is accompanied by the word POISON in red and the skull and crossbones prominently displayed on the label.
  • WARNING is the term used to identify materials that have a moderate hazard potential.
  • CAUTION is the term used to identify those products that have the least level of potential hazard.

Some products which are very dangerous to the applicator require the statement “RESTRICTED USE ONLY”. These products are available only to those that have an applicator’s license from the Texas Department of Agriculture.

Steps to Take Should Someone Become Accidentally Exposed to a Pesticide

  1. If someone is accidentally exposed to a pesticide, remove the contaminated clothing and wash immediately with soap and water. Do not use an abrasive cleaner, as this would allow the pesticide to penetrate the surface of the skin.
  2. If someone is exposed to pesticide vapors, get them to fresh air, and begin artificial respiration if they have stopped breathing.
  3. If the pesticide was splashed into one’s eyes, flush the eyes for 15 min. with clean water.
  4. If the material was accidentally ingested, read the label and carefully follow the instructions. Never give anything by mouth to an unconscious person.
  5. Take the person to the hospital for a thorough examination.
  6. When taking a person to the hospital, be sure to take the label and the container. This will help the doctor to prescribe the proper treatment. If information on the treatment for a specific pesticide is needed, the doctor can call either 800-424-9300 or 800-858-7378.

Information Contained On Pesticide Label

Before using any pesticide, read and follow the label carefully. Pesticide labels contain valuable information which should be read carefully. A current label is the final guide and should be followed.

The following information is printed on the label:

  1. Information about the chemical and concentration:
    • Trade name Ex: Bravo 720
    • Percent active ingredient is next on the label. EX: Chlorothalonil 54%.
    • Patents are listed in this section.
    • Hazard warnings, this is sometimes in both English and Spanish.
    • EPA registration number. This shows that the product has received EPA approval for the uses listed on the label.
    • Some labels will have an emergency assistance telephone number.
  2. General information on the label includes:
    • General comments on activity of the product.
    • Cautions about mixing with other products.
    • Precautionary statements.
    • Hazards to humans and domestic animals.
    • First aid.
    • Environmental hazards.
    • Directions for use.
    • Clothing and safety requirements.
    • Mixing and rate of water per acre suggestions.
    • Rotation restrictions.
    • Reentry period is the period between application and workers can reenter the area without protective clothing. In Texas there is a minimum of 24 hours. Depending on the pesticide the period can be much longer.
    • Application and calibration techniques.

Specific crops, pests, rates per acre, and application directions are covered on the label.

The following information on pesticide handling and container disposal is on the label.

  • Proper storage.
  • Instructions on how to dispose of unused pesticide solution or guidance on who to contact about safe disposal of the product.
  • Guidance on disposal of the empty pesticide container.

The warranty and limitation of damages are part of the label. One statement in this section suggests that if a product is improperly used, the company is not liable for damages. It is important that producers read and follow the label.

Pesticide Storage

The following general rules should be followed in storage of pesticides:

  • Store pesticides safely to prevent leaking and to aid inspection.
  • Do not store in unmarked container.
  • Do not store pesticides in containers used to store food, feed, beverages or medicine.
  • Do not store pesticides in an area where they can contaminate, food, feed, beverages.
  • Store pesticides according to the label.
  • Store pesticides behind locked doors to prevent unauthorized access to the materials.
  • Store the products in a dry, well-ventilated area and out of direct sunlight.
  • Storage area should be free of combustible material.
  • Storage area should be protected from freezing temperatures.

Disposal of Pesticide Containers

Check with the product label for disposal instructions. Also, the state regulatory agencies such as TDA and TWC have specific disposal information.

Worker Protection

Applicators of pesticides are responsible for the safety of workers who are working in or near fields treated with pesticides. Producers and applicators should be familiar with the following publications:

  • A Guide To The Texas Agricultural Hazard Communication Law Right-To-Know
  • Farm Laborer Laws: Summaries by Texas Agricultural Extension economists.
  • Texas Agricultural Hazard Communication Law 1988
  • Texas Pesticide Laws 1988
  • Texas Pesticide Regulations, September 1988
  • Texas Herbicide Law, Chapter 75, Texas Agricultural Code, TDA Q105E
  • Texas Herbicide Regulations 1987, TDA Q103K
  • Specific Crop Sheets
  • Texas Department of Agriculture Pesticide Application Record, TDA Q527A

The above publications and forms can be obtained from the Texas Department of Agriculture, P.O. Box 12847, Austin, Texas 78711. The telephone number is 512-463-7547.

Groundwater Contamination

Groundwater is the source of water for wells and springs; it fills spaces between particles of soil or cracks in bedrock. Geological formations containing groundwater are called aquifers.

Groundwater is widely used for household and other water supplies. Approximately half the population in the United States relies on groundwater for drinking water, and more than 90% of rural residents obtain their water from groundwater through wells and springs. There is increasing concern about groundwater contamination with pesticides and other contaminates. Properties of the pesticide, soil properties, and conditions of the site and management practices are the four factors which determine if a pesticide is likely to reach groundwater. Application methods, pesticide rates and timing are management practices which influence the possibility of groundwater contamination. Materials which are injected or incorporated into the soil have a much greater risk of getting into the groundwater than materials which are sprayed onto the plant. Higher rates of pesticides are more likely to contaminate than lower rates. Avoid applying materials during periods of heavy rainfall except where absolutely necessary.

Sources of Additional Information:

  1. Anonymous. 1987. Using Pesticides, Commercial Applicator Manual. Texas AgriLife Extension
  2. Anonymous. 1989. North Carolina Agricultural Chemicals Manual
  3. Anonymous. 1989. Spray Manual Catalog 41. Spraying Systems Co., Wheaton, Illinois, 60187
  4. Anonymous. Calibration. Texas AgriLife Extension
  5. Anonymous. Material Safety Data Sheet (MSDS) for Specific Pesticide, Available from Pesticide Dealer or Manufacture
  6. Anonymous. Pesticide Exposure – Protective Measures. L-1167. Texas AgriLife Extension
  7. Lipe, John. Calibrating a Backpack Sprayer for Herbicide Application. Texas AgriLife Extension
  8. Kroon, C.W. 1978. Liquid Calibration Handbook. Thompson Publications, P.O. Box 9335,Fresno, CA. 93791
  9. Valco, T.D. Chemical Application, Easy, Precise and Safe. Texas AgriLife Extension

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