APHIS Factsheet

Plant Protection and Quarantine April 2007

Using Malathion to 

Eradicate the Boll 

Weevil in Tennessee

Q. What is malathion and how is it used?

A. Malathion is an organophosphate insecticide 

that is commonly used to control pests in homes, 

gardens, and orchards. It is one of the safest 

pesticides available. There are many uses for 

malathion, including agricultural and human health 

uses. In an agricultural setting, malathion is used 

to eliminate pests, like boll weevils and exotic fruit 

flies, that threaten the productivity of important crops 

like cotton and citrus. In urban areas, malathion is 

used to control mosquitoes that can carry West Nile 

virus and other diseases of public health importance. 

Malathion is also used as an insecticide to control 

pests in homes and personal gardens. In addition to 

controlling agricultural pests, malathion is approved 

by the U.S. Food and Drug Administration as a 

prescription drug for the treatment of head lice on 

humans.

Q. What is the Southeastern Boll Weevil Eradication Program?

A. This program is a cooperative effort in which 

State and Federal officials work with local cotton 

growers to eradicate the boll weevil incrementally 

from the southeastern United States. Since 1892, 

the boll weevil has plagued U.S. cotton farmers. 

Boll weevil eradication began with a successful trial 

program in North Carolina and southern Virginia in 

1978. Since then, the southeastern program has 

expanded to include operations in Alabama, Florida, 

Georgia, Mississippi, Missouri, South Carolina, and 

Tennessee.

 A similar program has been completed in 

Arizona, California, Kansas, New Mexico, and 

adjacent areas of Mexico. In addition, growers in 

Arkansas, Louisiana, Oklahoma, and Texas are also 

involved in the active eradication of the boll weevil.

Q. Why is malathion used to eradicate the boll 

weevil?

A. Prior to the implementation of the weevil eradication program, farmers had their own chemical 

treatment methods to counteract the destructive boll 

weevil. Many of these methods were much less

environmentally friendly than malathion and less effective. Without a total eradication plan that included all 

cotton fields, farmers worked individually to control 

the pest, treating their fields many times each season, 

only to do the same thing again year after year. 

 One of the main goals of the eradication program 

is to eliminate the growers’ continual need for these 

potent pesticides. The end result of the program’s 

efforts will be a drastic reduction in the overall use of 

pesticides by cotton farmers. In other States that have 

already eradicated the boll weevil, pesticide use has 

dropped by as much as 40 to 100 percent, with growers in many areas no longer treating at all.

 Without the help of the Boll Weevil Eradication 

Program, farmers would have no choice but to revert 

back to their previous ways in an effort to protect their 

cotton crop and their livelihood. This is why the vast 

majority of the Nation’s farmers have voted to fund 

their local eradication efforts. 

Q. How much malathion is used?

A. The amount of malathion needed to effectively kill 

the boll weevil is very small. Only 10-16 fluid ounces 

of malathion are used to treat each infested acre 

(43,560 square feet). That’s like taking less than one 

can of soda and evenly distributing it over an entire 

acre. 

Q. How is the malathion applied? 

A. Both aerial and ground applications of malathion 

may be used depending on the size and location of 

the cotton fields. Aerial applications are performed 

with small fixed-wing aircraft and some helicopters. 

Ground applications involve the use of high-clearance 

tractors or truck-mounted sprayers controlled by the 

driver. The malathion is released at an ultra-low volume, and directed onto the cotton plants in each field, 

where it effectively controls boll weevils.

 The Boll Weevil Eradication Program uses careful 

precision, including global positioning systems (GPS), 

to apply malathion to cotton fields. Because of application techniques and the rural location of most cotton 

fields, the risk of human exposure is low. Unlike other 

eradication programs that spray entire areas, the boll 

weevil program only targets infested cotton fields, 

further minimizing human exposure. Some residents 

living next to cotton fields, however, may on rare 

occasions experience minimal drift, which involves a 

very small fraction of the applied material. In situations where homes or other sensitive sites are in close 

proximity to infested cotton fields, program personnel 
monitor the treatments by using oil-sensitive dye 

cards between the edge of the field and the sensitive site. Very small amounts of drift can be identified by these cards, allowing personnel to adjust the 

treatment or reschedule it when the conditions are 

more favorable, thus reducing the risk of exposure. 

The Boll Weevil Eradication Program monitors its 

malathion activties very closely, and is committed 

to working with homeowners who have questions or 

concerns about malathion drift or exposure. 

Q. How often does the eradication program plan 

to spray each cotton field?

A. It takes about three or four seasons to eradicate 

the boll weevil. Prior to the first full season, all fields 

are treated several times in the fall to kill as many 

weevils as possible before winter. The first kiling 

frost usually marks the end of treatment for the 

season.

 During the first full season, spraying is limited 

only to fields where infestations are detected. Traps 

are used to determine whether boll weevils are present in each field. The number of times each field is 

treated depends on whether additional boll weevils 

are found following malathion applications. On 

average, fields are treated about seven times during 

the first full season, although many fields will require 

few, if any, treatments.

 Similar operations are performed during the 

second full season of the program. If all goes as 

planned, by the third or fourth season eradication 

should be almost complete. Spraying will occur 

only in fields where the boll weevil continues to be 

detected. The use of malathion should be minimal 

considering most fields should already be free of the 

boll weevil. At the end of the third or fourth season, 

the program’s eradication efforts should be successful, with cotton growers beginning to experience 

better yields, much lower production costs due to 

reduced pesticide use, and an increase in the value 

of their land. 

Q. Why does the program use airplanes to treat 

the cotton fields? 

A. In order to successfully eradicate the boll weevil, 

hundreds of thousands of acres of infested cotton 

fields must be treated with malathion within very 

short periods of time. It’s not feasible to conduct 

such an extensive eradication program without 

aerial application. Aerial applicators are capable 

of treating fields much more efficiently and just as 

effectively as ground units. Without airplanes, the 

Boll Weevil Eradication Program would last longer 

and be much more expensive. Helicopters are 

also effective, but there are not enough in the area 

to fully support the program or replace the use of 

planes. 

 Cotton fields, which have traditionally been treated 

by growers with ground equipment, may be treated 

by airplanes during boll weevil eradication. Ground 

equipment will continue to be used near sensitive 

sites. 

Q. What precautions are taken to avoid spraying 

houses, businesses, and other public buildings 

next to cotton fields?

A. The Boll Weevil Eradication Program uses satellite 

guidance (GPS) and mapping technology to ensure 

that only cotton fields are treated with malathion. 

Aerial applicators are trained to fly with precision 

and spray fields targeted for boll weevil eradication. 

Satellite tracking enables program personnel to print 

the flight paths of every plane used by the eradication 

program. This information is helpful if there is ever a 

question about whether a plane sprayed beyond the 

boundaries of a specific cotton field. 

 Great care is taken to ensure that schools, hospitals, churches, and other sensitive locations are 

identified before any spraying takes place. When 

cotton fields are adjacent to these buildings, ground 

equipment is frequently used for treatment in order to 

reduce the potential for any drift. Spraying does not 

occur near schools while classes are in session, or 

while after-school activities are taking place.

 In addition, the program’s aerial and ground sprayers always adhere to strict rules regarding weather 

conditions in order to limit the potential offsite drift from 

the cotton fields. If the wind blows above 10 mph, or 

toward a sensitive site, treatments are stopped until 

favorable conditions return.

Q. Is it okay to be outside when malathion is being 

sprayed on nearby cotton fields?

A. Malathion is scientifically proven save and effective when used properly. When applied in accordance 

with the rate of application and safety precautions 

specified on the label, malathion can be used without 

posing a significant risk to human health. However, 

the program recommends that people who live next 

to cotton fields remain indoors during the brief spray 

interval in order to minimize any potential exposure. 

If you have questions about when the fields near your 

house will be sprayed, please call the Tennessee program office at (731) 772-8763 and someone will give 

you a general timeframe for the application. This will 

allow you to make plans to be inside, run an errand, or 

move to an alternate location if you desire during the 

short treatment period. Changing weather conditions, 

however, may affect spray times, so it may be necessary for the program to adjust its treatment schedules. 

Q. What will happen if I’m exposed to malathion 

while the program is spraying nearby fields?

A. Because the program is treating only infested 
cotton fields with malathion, it is unlikely that anyone 

will come into direct contact with the pesticide. 

 Historically, people exposed to malathion 

experience no reaction at all. As mentioned before, 

it’s frequently used in the home and garden as an 

insecticide. Some people, however, may experience minor reactions. Symptoms will generally clear 

within an hour or two of exposure, and will cause no 

residual effects.

 To prevent such exposure, people should avoid 

being outside in the immediate treatment area for 

about 30 to 60 minutes after the spraying takes 

place. Residents immediately adjacent to an area 

where spraying is taking place may want to keep 

doors and windows closed during the brief application period.

 Studies of laboratory animals show some suggestive evidence that malathion may be carcinogenic at extremely high doses over extended 

periods of time. These levels are thousands of 

times higher than a person would ever encounter, 

even if they stood in a cotton field and were sprayed 

directly with malathion each time the field was 

treated.

Q. How does malathion affect people with allergies, asthma, or other special health problems?

A. Malathion may affect people with these preexisting health conditions. If you’re concerned, 

please contact your doctor or a health professional. 

 

Q. Is the spray harmful to pets?

A. The program recommends that pets be kept 

inside during treatment. Pets that are exposed 

to malathion should not experience any residual 

effects. If you think your pet may have come into 

contact with malathion after walking through dewcovered cotton plants following a treatment, give it a 

bath to remove any contamination. 

 Malathion can be toxic to fish. If your small pond 

is adjacent to a cotton field, the program recommends covering it, especially if the pond is less than 

three-feet deep. Such ponds should be uncovered 

shortly after the aerial application to prevent oxygen 

depletion.

Q. What if malathion gets in my backyard 

swimming pool?

A. Malathion for boll weevil eradication is applied 

directly to infested cotton fields. If a limited amount 

enters a shallow pool, there is little health risk for 

swimmers. If a shallow pool (2 feet or less) is accidentally sprayed with malathion during an aerial boll 

weevil application, as a precaution, people should 

avoid swimming in the pool for 24 hours. If a pool 

is deeper, the risk decreases greatly and swimming 

can commence sooner. If you are concerned that 

malathion may have drifted into your pool, please call 

your local eradication program office. Environmental 

monitoring specialists can place dye cards next to 

your pool prior to the next treatment to determine if 

any malathion is getting near your pool. If no spots 

are visible on the cards, malathion has not drifted into 

the area. If spots do appear, the dye cards can be 

analyzed to determine the amount of malathion and 

ensure that it is far below any level of concern. 

Q. How long will malathion residue remain in 

yards? 

A. Residues from malathion applications are shortlived. Malathion should dry on grass, vegetation, and 

other outdoor surfaces within 2 hours. On especially 

humid days, malathion may take longer to dissipate. 

As a precaution, you can use a hose to wash off 

outdoor household articles, including swing sets and 

picnic tables, following treatments in adjacent fields. 

To further reduce any risk of exposure, wear shoes 

and socks if you live next to a cotton field and plan to 

be outside following a treatment. 

Q. Is it safe to eat food from my garden if I live 

next to a cotton field that’s being treated?

A. Yes. Malathion is commonly used in homes and 

gardens. As with any produce, of course, it’s important to thoroughly wash your fruit and vegetables 

before serving. If you’re concerned about exposure, 

samples can be taken from your garden and tested 

for malathion, assuming you are not already using it to 

protect your own vegetables against insects. 

Q. Who can I contact for more information?

A. If you have questions about the program, please 

call the Tennessee program office at (731) 772-8763.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, 

national origin, age, disability, and where applicable, sex, marital 

status, familial status, parental status, religion, sexual orientation, 

genetic information, political beliefs, reprisal, or because all or part 

of an individual’s income is derived from any public assistance 

program. (Not all prohibited bases apply to all programs.) Persons 

with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) 

should contact USDA’s TARGET Center at (202) 720–2600 (voice 

and TDD). To file a complaint of discrimination, write to USDA, 

Director, Office of Civil Rights, 1400 Independence Avenue, S.W. , 

Washington , D.C. 20250–9410 , or call (800) 795–3272 (voice) or 

(202) 720–6382 (TDD). USDA is an equal opportunity provider and 

employer. 

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture