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Agricultural chemical drift and its control

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Title:
Agricultural chemical drift and its control
Series Title:
Circular
Creator:
Cromwell, Richard P
Florida Cooperative Extension Service
Place of Publication:
Gainesville
Publisher:
Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date:
Language:
English
Physical Description:
7 p. : ; 28 cm.

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Subjects / Keywords:
Pesticides -- Environmental aspects -- United States ( lcsh )
Spraying and dusting residues in agriculture ( lcsh )
Genre:
non-fiction ( marcgt )

Notes

General Note:
Title from caption.
General Note:
"June 1993."
Statement of Responsibility:
Richard P. Cromwell.

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University of Florida
Holding Location:
University of Florida
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This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.
Resource Identifier:
AAA6836 ( LTQF )
AJQ6973 ( LTUF )
28532397 ( OCLC )
021862241 ( ALEPH )
Classification:
101 F636c 1105

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I0 UNIVERSITY OF

FLORIDA

Florida Cooperative Extension Service


Agricultural Chemical Drift and Its Control'


Circular 1105
June 1993


Richard P. Cromwell2


INTRODUCTION

Drift is the airborne movement of particles into
nontarget areas. It is both undesirable and, to a
degree, unavoidable. Drift problems can be minimized
by understanding what causes it and following
recommended procedures for limiting it.

The fear of chemical drift is out of proportion to
the threat that it poses to people and the environment.
This statement is supported by a video tape, "Big
Fears, Little Risks," presented by The American
Council on Science and Health. In this video tape,
Dr. Bruce Ames, a scientist at the University of
California, Berkeley and the developer of the Ames
test, a widely used test to determine the carcinogenic
nature of chemicals, states that the low levels of
chemicals in the environment are much less of a threat
to human health than life-style related factors such as
smoking, diet, sexual behavior, and others.

What about the threat of chemicals that drift from
treated fields and settle directly onto unsuspecting
people? Workers in adjacent fields have been
accidently sprayed by drift and received a dose
sufficient to cause serious illness. However, the safety
specialist at both the University of Florida in
Gainesville, FL, and the University of California in
Davis, CA, two of the more important agricultural
states, do not recall any documented cases of a person
's death being caused by spray drift. People have died
from accidental poisoning by agricultural chemicals,


but they were either mixing or loading the
concentrated chemical and were not using procedures
recommended on the product label.

Although hazardous pesticide residues on produce
grown in the United States is a rare occurrence, it is
still a major public concern. A 1984 consumer survey
showed that of all the possible harmful products found
in food, the public worried most about pesticide
residues. Because the public perceives that pesticides
in our food supply is a major problem, applicators of
pesticidal chemicals should apply them wisely to
minimize drift and to avoid drift problems. Some
recommended procedures for minimizing drift are
presented in this publication.

Note: The remainder of this publication will primarily
refer to pesticidal particles as droplets because the
majority of pesticides are applied as sprays. However,
small particles of dry material are also prone to drift.
Pesticidal dusts were once the most common
formulation used in agriculture in the late 1940's when
the use of synthetic pesticides became a common
practice. Dusts are seldom used in agriculture today
because they are so prone to drift from the target
area.


1. This document is Circular 1105, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Publication date: June 1993.
2. Richard P. Cromwell is Associate Professor and Extension Specialist, Cooperative Extension Service, Institute of Food and Agricultural Sciences,
University of Florida, Gainesville FL 32611.
The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational
information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national
origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office.
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean


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Agricultural Chemical Drift and Its Control

SWATH DISPLACEMENT LONG RANGE
DRIFT


SCIENCE Drift is comprised of two components, "swath
Lk$bgay displacement" and "long range drift". Swath
displacement is the lateral movement of relatively
large droplets 150-200 micrometers or larger (spray
droplets are measured in micrometers; 1 inch is equal
to 25400 micrometers) for a short distance. Swath
displacement can cause relatively high residues in
nearby fields.

Long range drift is the movement of small droplets
for great distances (miles from an application site) and
often over a wide area. The resulting level of residue
is usually very low, but can cause a problem when the
chemical settles on a crop that is highly sensitive to
that particular chemical.

FACTORS THAT INFLUENCE DRIFT

The primary factors that influence drift are droplet
size, wind speed, humidity, formulation of the
pesticide, height of emission (primarily influences
swath displacement of large droplets), and the size of
the area treated with the pesticide. The factor that
has the greatest influence on the downwind movement
is droplet size.

Droplet Size

Droplet size is the single most important factor
that affects the distance that a droplet will drift from
the target area. The vertical velocity (settling velocity)
at which a droplet falls to the ground depends on the
size of the droplet. The settling velocity varies
approximately as the square of a droplet's diameter.
A 400 micrometer droplet would fall 4 times as fast as
a 200 micrometer droplet and would drift 1/4 as far
when transported at equivalent wind speeds.

Wind Speed

Wind speed influences the drift distance of
droplets, but does not have as great an influence as
droplet size. The distance that a droplet drifts is
approximately proportional to the wind speed. A
large droplet will travel twice as far in a wind twice as
fast.


Page 2


Humidity

Droplets are reduced in size due to evaporation
of the volatile portion of the spray. Therefore,
droplets that are not particularly drift-prone during
humid conditions might become small enough to drift
from the target area when the humidity is low.

Sometimes applicators in the cotton growing
regions of the South apply pesticides in as little as 1/2
gallon per acre of crop oils (soybean or peanut oil).
Normally the pesticide might be applied in water at a
higher rate per acre. The reason that some
applicators give for using oil as a diluent is that it does
not evaporate; and, therefore, does not pose a drift
problem. This is not necessarily true because the
small amount of spray applied must be highly
atomized to achieve coverage and is drift-prone
without the effect of evaporation.

Formulation

Aerial applicators are often called "crop dusters"
because most of the pesticides applied during the early
years of aerial application (late forties and fifties) were
formulated as dusts. Aerial applicators are "crop
dusters" in name only in today's agriculture. Most
applicators switched to sprays and granular
applications to reduce drift problems. Dusts are the
most drift-prone pesticide formulation because the
particles are very small.

Many pesticides are oil based formulations known
as emulsifiable concentrates (EC) because many
pesticidal chemicals are soluble in oil. These
formulations form a white, milky emulsion when
mixed with water. If a large droplet spectrum is used
to apply the emulsion, the resulting spray is not
particularly drift- prone. If the droplet spectrum
produced by the nozzle is small, the water phase of
the mixture can evaporate leaving nothing but a small
oil droplet that is prone to drift.

Some formulations of pesticides are more volatile
than others and the vapor phase of the chemical can
drift and cause problems outside of the target area.
The herbicide, 2,4-D, is formulated as an amine and
an ester. The ester formulation is often more
effective, but is more volatile. Ester formulations are
banned in some areas because some broadleaf crops
like tomatoes and melons are extremely sensitive to
2,4-D and even small concentrations of the chemical
vapor in a distant nontarget field can cause plant
injury.







Agricultural Chemical Drift and Its Control


The least drift-prone formulations of pesticides are
pellets and granules. The use of these formulations
is somewhat limited because they cannot be used to
apply chemicals to plant foliage. They are widely used
to apply chemicals to the soil or when treating aquatic
weeds.

Height of Emission

The time that large droplets remain airborne and
consequently the time that the wind has to act on
them depends on the height of the nozzle above the
ground.

The emission height of small droplets is not
necessarily a major factor in determining distance that
it might drift. The weight of a small droplet is very
small and it can actually rise rather than fall because
upward components of the wind can generate friction
forces larger than the droplet's weight. A small
droplet can be emitted from a nozzle close to the
ground (18 inches or standard boom height) and
remain aloft much longer than a larger droplet emitted
at a much higher height.

Size of the Treated Area

This factor tends to be overlooked by many
applicators of agricultural chemicals. The amount of
residue that drifts onto a neighboring crop after
treating 10, 20, or 50 acres might not cause damage to
the crop, but at some number of acres the residue
level can cause damage. Because the amount of
residue in surrounding fields depends on the number
of acres treated in the target field, an applicator
should spread out the treatment of large fields over as
many days as feasible. This increases the chances of
the drift being spread out by various wind directions
at a residue level low enough to avoid crop damage.

The size of the area that can be treated by an
aircraft in a short period of time is what causes many
drift problems related to aerial application. It is often
reasoned that aircraft cause drift problems because of
the relatively high height of the spray boom. The
height of the spray boom can cause high residues in
an adjacent field due to swath displacement, but
probably is not a major factor in the level of residue
in more distant fields.

Airblast sprayers that are sometimes used to treat
low growing crops generally produce a very small,
drift-prone droplet spectrum. These sprayers are used
because they can cover a wide swath (40 to 80 feet)


without a cumbersome wide boom. If enough of these
sprayers were placed in a field so that approximately
1000 to 1500 acres could be treated in a day (an
acreage treatable by an aircraft), the resulting drift
problem in distant fields could be much greater than
one caused by an aircraft because there is a greater
percentage of small droplets emitted by the sprayers.

NOZZLES PRODUCE A WIDE SPECTRUM OF
DROPLETS

Drift would be much less of a problem, if nozzles
were available that could produce a narrow range of
droplet sizes with no droplets below approximately
150-200 micrometers in diameter. Commercially
available hydraulic nozzles produce a wide droplet
spectrum with droplets ranging from below 100 up to
500 micrometers and larger. The extremes on both
ends of the spectrum are not very effective in
controlling most pests. The small droplets are prone
to drift from the target field and the extremely large
ones contain a lot of pesticide that does not effectively
contribute to plant coverage.

Large droplets are not very effective in achieving
plant coverage because the volume of a droplet varies
as the cube of the droplet diameter. Neither a 250
nor a 500 micrometer droplet are very prone to drift
from the target field because both quickly settle to the
ground. A 500 micrometer droplet contains eight
times the pesticide as the 250 micrometer droplet and
this pesticide would be far more effective, in relation
to coverage, if it were in eight 250 micrometer
droplets. An ideal nozzle would produce droplets in
the 250 to 300 micrometer range. These droplets
would be large enough to avoid long range drift
problems, but small enough to yield acceptable spray
coverage. These droplets drift a very short distance
because the wind does not have much time to act on
them before they reach the ground.

SWATH DISPLACEMENT IS PREDICTABLE

Swath displacement is usually about 25 feet for
low pressure ground sprayers and up to 300 feet for
sprays applied by aircraft. Swath displacement is the
predictable component of chemical drift and is
dependent on the droplet size, the height from which
the droplet is released, and the wind speed. If swath
displacement was the only component of drift, drift
would not be as serious of a problem as it is. A
pesticide applicator would merely leave a buffer strip
between the last rows of the treated field and an


Page 3







Agricultural Chemical Drift and Its Control


adjacent field that would be wide enough to avoid
contaminating the nontarget field.

LONG RANGE DRIFT IS NOT PREDICTABLE

Long range drift of small droplets is not
predictable because a small droplet does not always
fall while suspended in air. Air can have a vertical
velocity component which is generally upward during
the middle of the day when the warm air at ground
level is displaced by the cooler, heavier air above it.
The vertical updraft can cause a friction force on a
small droplet that is greater than the droplet's weight.
When the upward force exceeds the droplet's weight,
the droplet will rise rather than fall. To make
matters worse, the weight of a spray droplet reduces
over time because water (most spray droplets are
predominantly water) in the droplet evaporates.

A small droplet will remain airborne until the air
mass transporting the droplet is calm long enough to
allow the small downward force of gravity to cause it
to settle to the ground. Because weather is
unpredictable, accurately predicting where a small
airborne droplet will eventually land is essentially
impossible. The location is largely a matter of chance.
There are computer models used to determine where
droplets will settle under given environmental
conditions. These models predict the paths taken by
the larger droplets, but are not very accurate when
predicting where the small droplets settle out. These
programs are useful for determining how wide a buffer
zone should be to keep swath displacement from
causing problems in nearby fields. Fortunately the
residue level that accumulates because of long range
drift is usually very low and often undetectable.

Whether the low level of chemical that results
from long range drift constitutes a problem depends
on who is asked. There are some people who feel
that chemicals settling on nontarget areas at any level
is a problem. If the only acceptable level of drift into
nontarget areas was zero, all spray operations would
have to be shut down along with many industrial
operations. There is no such thing as "zero drift" for
any operation where small particles are released into
the atmosphere. Even large objects are displaced
some small amount when falling in air that has an
horizontal wind velocity. However, it is possible to
keep drift to a such a low level that the benefits from
applying a chemical exceed the potential risks in the
minds of most rational people. If this were not so, the
application of the chemical would not be allowed by


the Environmental Protection Agency (EPA), the
agency that regulates agricultural pesticides.

DRIFT CAN OCCUR AT THE TIME OF
APPLICATION OR LATER

Chemicals can drift from the target area and cause
a drift problem at the time of the application or at
some time after the application. Drift that occurs
after the application are caused by: (1) having the dry
residue of a wettable powder applied as a spray blown
into an adjacent area after the water carrier
evaporates, (2) having chemical vapors transported
downwind or (3) having high winds blow pesticide-
treated soil and plant particles from the target field
into a neighboring area some time after the chemical
was applied. Contamination resulting from a chemical
being transported into nontarget areas hours or even
days after application are an oddity. Very few of the
problems caused by drift have resulted from "post
application" drift. This publication is primarily
concerned with the drift of particles that begin their
flight into neighboring areas at the time of application.
This is the type of drift that is most prevalent and
deserves most of the attention.

DRIFT AND DRIFT PROBLEMS

There is a difference between drift and drift
problems. Virtually all spray applications result in
some small amount of spray drifting beyond the
immediate target area. This does not mean that the
drift has created a "problem".

The chemical may drift from the target area onto
an area totally within the holdings of the person
applying it. This person probably would not consider
the drift to be a problem. If the chemical drifts onto
a nontarget area not totally within the holdings of the
person applying it and the residue level is too small to
cause an immediate effect (offensive odor, illness of
residents, damage to plants, etc.), there probably will
not be a problem caused by the drift. Chemicals used
in today's agriculture are less likely to accumulate in
the soil or water because the pesticides that are used
are degraded by the effects of sunlight and soil
microorganisms. Rapid degradation without
accumulation of a chemical or its breakdown products
is a major consideration in determining whether the
chemical can be used as a pesticide.

For example, chemicals that remain as toxins in
the environment for a long time (years in some cases)
are known as persistent pesticides and the use of this


Page 4







Agricultural Chemical Drift and Its Control


type of chemical has been limited severely by the
Environmental Protection Agency. The chlorinated
hydrocarbons (DDT is the most renowned chemical
in this group) are an example of a pesticide group that
remained in the environment for years. These
chemicals were very effective pesticides with low
mammalian toxicity, but they accumulated over time
in the environment. DDT caused the egg shells of
birds of prey like the bald eagle to be very thin and
they often cracked before the young eaglets hatched.

IPM HAS REDUCED RELIANCE ON
CHEMICALS

In Florida, there is probably less drift of chemicals
into nontarget areas today than in the past because
growers are not relying solely on chemicals to control
pests. Growers are using "Integrated Pest
Management (IPM)" in their fight against pests. IPM
is an ecological approach to pest management that
often provides economical, long-term protection from
pest damage or competition. Concern about pesticides
in the environment and their potential harm to users
and the public spurred the interest in IPM. The
practitioners of IPM use a combination of pest control
methods to prevent their crops from suffering
economic losses. A few examples of nonchemical pest
control methods used by growers are: (1) planting
crop varieties that have natural resistance to pests, (2)
crop rotations that have proven to be helpful in
reducing pest problems, and (3) chopping and burying
residues from the previous year's crop.

IPM does not exclude the use of chemical control
methods, but chemical use is reserved as the last line
of defense in the growers' battle against pests.
Sometime data collected in the field show that the
pest numbers are high enough to warrant a chemical
application to avert serious economic losses in spite
of the grower using all of the best nonchemical
measures to avoid pest problems. When the decision
to apply a chemical is made, growers using IPM try to
choose a chemical that will kill the target pest while
sparing many of the beneficial insects that prey on
various pests in the field. Preserving beneficial insects
can prevent or at least delay having to apply chemicals
in the future.

DRIFT WILL PROBABLY DECREASE WHILE
DRIFT PROBLEMS INCREASE

Even though the application of agricultural
pesticides is not increasing in Florida because of the
use of IPM (pesticide use in citrus, one of Florida's


major crops, has decreased considerably), the number
of drift-related problems could increase. Many people
are moving to Florida and developments are being
built ever closer to long standing agricultural
operations. Many of these people are terrified at the
thought of an agricultural pesticide, regardless of the
level of residue, drifting into their residential area.

A large portion of Florida residents pay to have
pest control operators apply levels of pesticides that
have been scientifically tested for efficacy and safety
inside their house and in their yard. If the same level
of residue of the chemical occurred in the yard
because of spray drifting from an agricultural pest
control operation, it would probably be a matter of
great concern to residents in the area. This-is
somewhat perplexing, but understandable. The benefit
received from the pest control operator's application
is the obvious absence of roaches, fleas, chinch bugs
or whatever pest that plagues the homeowner. People
do not see the benefit of agricultural pest control "first
hand". Even though the public is told that agricultural
pesticide use makes for high quality, low cost food, the
benefit is not as obvious as the absence of household
pests.

Another reason for the strong potential for more
drift problems in the future, in spite of possibly less
drift, is the relatively new field of Environmental Law
coupled with equipment capable of detecting the
presence of extremely low levels of any substance.

WHAT CAUSES DRIFT?

The distance that a droplet moves laterally when
released in air depends on the time the droplet is
airborne and the average horizontal velocity of the
droplet during this time period. The distance can be
calculated with the equation below:


Drift Distance = suspension time
horizontal velocity


x average


This equation is simple enough, if you know the
time that the droplet is suspended in the air and its
average horizontal velocity. However, determining
either the suspension time or the average horizontal
velocity of small droplets (100-150 micrometers or
less) is virtually impossible because they are
dependent on weather.


Page 5







Agricultural Chemical Drift and Its Control


Large Droplets Drift Very Little

The time that a large droplet is suspended in the
air depends on the height from which it is released
and its average velocity in the vertical direction. A
large droplet released in air will fall at an increasing
velocity until the droplet's weight is equal to the
upward force on the droplet due to air friction. When
these two forces are equal, the object will fall at a
constant velocity known as the terminal or settling
velocity.The terminal velocity of a large droplet is
relatively high because it takes high velocities to
generate enough friction force to balance the object's
weight. Depending on the height from which a large
droplet is released, it could strike the ground before
reaching its terminal velocity. Large droplets drift
very little primarily because their suspension time is
small.

Small Droplets Can Drift For Great Distances

The settling velocity of a small droplet is very low
because its weight is low. If the droplet is suspended
in air that has an updraft velocity greater than the
settling velocity of the droplet in still air, the droplet
will actually rise rather than fall.

The weight of most spray droplets diminishes with
time because the volatile portion of the spray droplet
evaporates. Evaporation reduces the weight of small
droplets more rapidly than larger ones because they
have more surface area relative to their mass.
Therefore, a small particle that consists primarily of
water is drift-prone initially and becomes even more
drift-prone with time.

Because the vertical velocity of small droplets can
be either down or up and the wind direction can
change during the extended time that a small droplet
is suspended, it is virtually impossible to predict the
distance that the droplet will drift. Neither the
suspension time nor the average horizontal velocity
can be predicted with any degree of certainty. A small
droplet will either completely vaporize or the
nonvolatile portion of the droplet (many spray
mixtures contain some small amount of nonvolatile
oil) will eventually settle to the ground due to the ever
present force of gravity. The air mass carrying the
droplet must remain calm for a relatively long time in
order for the droplet to settle out.


RECOMMENDATIONS FOR REDUCING
DRIFT AND DRIFT PROBLEMS

* Nozzles should be used that produce as large of
a droplet spectrum as possible while yielding
adequate plant coverage and pest control. Large
nozzle orifices and low spray pressure creates a
large droplet spectrum. It may be necessary to
apply higher than normal amounts of diluted spray
per acre when using large droplets to avoid drift
in order to get adequate coverage.

* Do not make applications during temperature
inversions. An inversion is a stable atmospheric
condition characterized by an increase in air
temperature with an increase in height above the
ground until at some height a barrier of cold air
is met. Use a column of smoke near the
application site to check for an inversion. The
smoke will rise to the level of the cold air barrier
and will then move laterally below it.

* Usually less material will drift from the target field
during an inversion, but the material that does
leave the target field remains in a more
concentrated cloud and the level of residue that
settles onto nontarget areas will be higher than
usual. Even though the amount of chemical that
drifts from the target area during an inversion is
often less, the potential for a drift problem can be
greater because the small droplets are not lofted
into the upper atmosphere, diluted and spread
over a large area.

* Make applications when the wind is blowing away
from any highly sensitive nontarget areas and the
wind velocity should range between 3 to 10 mph.
Extremely low winds are avoided because they
indicate inversion conditions and winds above 10
mph are avoided because relatively large droplets
can be transported into neighboring fields.

* Leave a buffer zone of approximately 300 feet
between the treated field and any particularly
sensitive areas. Buffer zones will avoid
contamination of neighboring areas by the
displacement of relatively large spray droplets.
However, buffer zones will not effectively
eliminate low level contamination of distant areas
by the small droplets formed by all commercially
available nozzles.

* The nozzles must provide adequate coverage and
pest control while minimizing small, drift prone


Page 6







Page 7


Agricultural Chemical Drift and Its Control

droplets. Request a droplet spectrum data sheet
from the manufacturer that gives information
about the percentage of the droplets that are
smaller than 150 micrometers. Use nozzles with
the smallest portion below this size.

Use the lowest pressure possible that will give
adequate coverage and control to limit the number
of drift-prone droplets.

Make the application at the minimum height that
provides a uniform spray pattern.

Shut off sprayers when turning at the ends of the
rows.

Spray early in the morning, late in the evening, or
at night, whenever possible, to avoid killing honey
bees.

ADDITIONAL RECOMMENDATIONS FOR
AERIAL APPLICATIONS

Orient the nozzles straight back to minimize small
droplet formation due to wind shear.

Limit the boom length to 75% of the wingspan of
the aircraft in order to prevent small droplets
from becoming entrained in the wing tip vortices
and contributing to drift problems.

Limit aircraft speed when applying chemicals that
crops in neighboring nontarget fields are
particularly sensitive to. Modern turbine powered
aircraft capable of flying in the 150 to 160 mph
range will create more small drift- prone droplets
at these speeds.

Dress the ends of a field with a couple of passes,
so that the sprayer does not have to be turned on
before the aircraft is level at the beginning of a
pass or left on after pulling up at the end of a
pass.

If a customer wants a field treated "now" when
conditions indicate a high potential for a drift
problem, explain to the customer why it would be
unwise to make the application under the existing
conditions.




Full Text

PAGE 1

Agricultural Chemical Drift and Its Control Page 2 /01 F (3 . SWATH DISPLACEMENT LONG RANGE Humidity ,,05 .


PAGE 1

Agricultural Chemical Drift and Its Control Page 3 The least drift-prone formulations of pesticides are without a cumbersome wide boom. If enough of these pellets and granules. The use of these formulations sprayers were placed in a field so that approximately is somewhat limited because they cannot be used to 1000 to 1500 acres could be treated in a day (an apply chemicals to plant foliage. They are widely used acreage treatable by an aircraft), the resulting drift to apply chemicals to the soil or when treating aquatic problem in distant fields could be much greater than weeds. one caused by an aircraft because there is a greater percentage of small droplets emitted by the sprayers. Height of Emission NOZZLES PRODUCE A WIDE SPECTRUM OF The time that large droplets remain airborne and DROPLETS consequently the time that the wind has to act on them depends on the height of the nozzle above the Drift would be much less of a problem, if nozzles ground. were available that could produce a narrow range of droplet sizes with no droplets below approximately The emission height of small droplets is not 150-200 micrometers in diameter. Commercially necessarily a major factor in determining distance that available hydraulic nozzles produce a wide droplet it might drift. The weight of a small droplet is very spectrum with droplets ranging from below 100 up to small and it can actually rise rather than fall because 500 micrometers and larger. The extremes on both upward components of the wind can generate friction ends of the spectrum are not very effective in forces larger than the droplet's weight. A small controlling most pests. The small droplets are prone droplet can be emitted from a nozzle close to the to drift from the target field and the extremely large ground (18 inches or standard boom height) and ones contain a lot of pesticide that does not effectively remain aloft much longer than a larger droplet emitted contribute to plant coverage. at a much higher height. Large droplets are not very effective in achieving Size of the Treated Area plant coverage because the volume of a droplet varies as the cube of the droplet diameter. Neither a 250 This factor tends to be overlooked by many nor a 500 micrometer droplet are very prone to drift applicators of agricultural chemicals. The amount of from the target field because both quickly settle to the residue that drifts onto a neighboring crop after ground. A 500 micrometer droplet contains eight treating 10, 20, or 50 acres might not cause damage to times the pesticide as the 250 micrometer droplet and the crop, but at some number of acres the residue this pesticide would be far more effective, in relation level can cause damage. Because the amount of to coverage, if it were in eight 250 micrometer residue in surrounding fields depends on the number droplets. An ideal nozzle would produce droplets in of acres treated in the target field, an applicator the 250 to 300 micrometer range. These droplets should spread out the treatment of large fields over as would be large enough to avoid long range drift many days as feasible. This increases the chances of problems, but small enough to yield acceptable spray the drift being spread out by various wind directions coverage. These droplets drift a very short distance at a residue level low enough to avoid crop damage. because the wind does not have much time to act on them before they reach the ground. The size of the area that can be treated by an aircraft in a short period of time is what causes many SWATH DISPLACEMENT IS PREDICTABLE drift problems related to aerial application. It is often reasoned that aircraft cause drift problems because of Swath displacement is usually about 25 feet for the relatively high height of the spray boom. The low pressure ground sprayers and up to 300 feet for height of the spray boom can cause high residues in sprays applied by aircraft. Swath displacement is the an adjacent field due to swath displacement, but predictable component of chemical drift and is probably is not a major factor in the level of residue dependent on the droplet size, the height from which in more distant fields. the droplet is released, and the wind speed. If swath displacement was the only component of drift, drift Airblast sprayers that are sometimes used to treat would not be as serious of a problem as it is. A low growing crops generally produce a very small, pesticide applicator would merely leave a buffer strip drift-prone droplet spectrum. These sprayers are used between the last rows of the treated field and an because they can cover a wide swath (40 to 80 feet)


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REPORT xsi:schemaLocation 'http:www.fcla.edudlsmddaitss http:www.fcla.edudlsmddaitssdaitss2Report.xsd' xmlns:xsi 'http:www.w3.org2001XMLSchema-instance' xmlns 'http:www.fcla.edudlsmddaitss'
DISSEMINATION IEID 'E20090919_AAABWX' PACKAGE 'UF00008572_00001' INGEST_TIME '2009-09-19T18:09:48-04:00'
AGREEMENT_INFO ACCOUNT 'UF' PROJECT 'UFDC'
REQUEST_EVENTS TITLE Disseminate Event
REQUEST_EVENT NAME 'disseminate request placed' TIME '2015-05-15T14:47:26-04:00' NOTE 'request id: 302274; This is a disseminate from UF Chelsea S Dinsmore for migration DigiTool to Islandora see CAS-56088-F3Z2' AGENT 'Stephen'
finished' '2015-05-15T18:11:26-04:00' '' 'SYSTEM'
FILES
FILE SIZE '194938' DFID 'info:fdaE20090919_AAABWXfileF20090919_AADUTL' ORIGIN 'DEPOSITOR' PATH 'sip-files00001.jp2'
MESSAGE_DIGEST ALGORITHM 'MD5' 4f6069dfeb29367372da4420da8fa430
'SHA-1' 390630960c10d721e17f44e5eeb968567474ee84
EVENT '2012-04-03T19:01:44-04:00' OUTCOME 'success'
PROCEDURE describe
'154915' 'info:fdaE20090919_AAABWXfileF20090919_AADUTM' 'sip-files00001.jpg'
26346e5e1bf59a51f336ba433380bd0c
657edd0a8da557be3df6388eb0d3c20fc481cdc9
'2012-04-03T19:01:30-04:00'
describe
'88843' 'info:fdaE20090919_AAABWXfileF20090919_AADUTN' 'sip-files00001.pdf'
df1c639161c2519bc6f1e208899d5b97
b63d5f2e4bbd99c30fb73b2b3b8afb32699afddd
'2012-04-03T19:01:37-04:00'
describe
'861740' 'info:fdaE20090919_AAABWXfileF20090919_AADUTN-norm-0' 'ARCHIVE' 'aip-filesF20090919_AADUTN-norm-0.pdf'
48c279620392bcf49e367d81b9512286
1d5e440b611127d699bf9932b2b9060ff387b025
'2015-05-15T18:10:57-04:00'
describe
'2015-05-15T18:10:42-04:00'
normalize
'100182' 'info:fdaE20090919_AAABWXfileF20090919_AADUTO' 'sip-files00001.pro'
981ed51776016503c5d31834c5676cda
beb993d3058da394ca3b4fab600316afc2ad2c2d
'2012-04-03T19:01:24-04:00'
describe
'42375' 'info:fdaE20090919_AAABWXfileF20090919_AADUTP' 'sip-files00001.QC.jpg'
2e188e9c71aa8b1303d056f3c22cb508
ef9470dc8b2d49dce5f98c6ed93f1473616c79ba
'2012-04-03T19:01:21-04:00'
describe
'1035891' 'info:fdaE20090919_AAABWXfileF20090919_AADUTQ' 'sip-files00001.tif'
4c02165bf7dc33f27f36e6cf2f02abbd
b9c1b31e82ac1dbebe357844b6a4d01c07b3d119
'2012-04-03T19:01:55-04:00'
describe
Invalid DateTime length:
WARNING CODE 'Daitss::Anomaly' Invalid DateTime length
Invalid DateTime length
'3923' 'info:fdaE20090919_AAABWXfileF20090919_AADUTR' 'sip-files00001.txt'
f71321eee5f73974be5b024d0f619e7f
4798d8ccce3c22aefe5fe72666c2ad4402c171d6
'2012-04-03T19:01:58-04:00'
describe
'10131' 'info:fdaE20090919_AAABWXfileF20090919_AADUTS' 'sip-files00001thm.jpg'
6667005ff0f7a4c8da3e287cedf6c585
0eaab40fe32ce284050b3949f20ce0b9dc4e7c79
'2012-04-03T19:01:56-04:00'
describe
'219022' 'info:fdaE20090919_AAABWXfileF20090919_AADUTT' 'sip-files00002.jp2'
39d101635af2ed72df017f6f890ff25b
3cfafcbe9716bd54a9c52d9e49559f7bf689222e
'2012-04-03T19:01:19-04:00'
describe
'172405' 'info:fdaE20090919_AAABWXfileF20090919_AADUTU' 'sip-files00002.jpg'
5fe2ff21dfa16853b00d1549a50d3fd6
e6d8b3cca1c423b4bf5dca6bf02d81a63d80a529
'2012-04-03T19:02:06-04:00'
describe
'97948' 'info:fdaE20090919_AAABWXfileF20090919_AADUTV' 'sip-files00002.pdf'
13067534fafb2926bef741d43b5077bc
8c40038874b3b7f2d66e0a05f0a621bb2230548a
'2012-04-03T19:01:39-04:00'
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUTV-norm-0' 'aip-filesF20090919_AADUTV-norm-0.pdf'
48c279620392bcf49e367d81b9512286
1d5e440b611127d699bf9932b2b9060ff387b025
describe
'2015-05-15T18:10:45-04:00'
normalize
'111902' 'info:fdaE20090919_AAABWXfileF20090919_AADUTW' 'sip-files00002.pro'
7d3de2fbf77b255b467854d0c59643eb
33e71b4ef081b81e0908212309dc6bb0cd59e856
'2012-04-03T19:01:53-04:00'
describe
'47196' 'info:fdaE20090919_AAABWXfileF20090919_AADUTX' 'sip-files00002.QC.jpg'
cea653e92020ee28d678da77d7671969
25909229a10740819518c0a04ac7e482d2975d6f
'2012-04-03T19:01:22-04:00'
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUTY' 'sip-files00002.tif'
6549465caadd2f2ab3b645a9bd89ad34
a6102e1d3b5325ba6f312582684cddd0d46ffd22
'2012-04-03T19:01:38-04:00'
describe
Invalid DateTime length:
Invalid DateTime length
Invalid DateTime length
'4808' 'info:fdaE20090919_AAABWXfileF20090919_AADUTZ' 'sip-files00002.txt'
a2bff0e1fbb3be40c96dc0b4d2cb4ada
c3f496d7fa05389fa82414454a5c3a29db2b497d
'2012-04-03T19:01:25-04:00'
describe
'11247' 'info:fdaE20090919_AAABWXfileF20090919_AADUUA' 'sip-files00002thm.jpg'
b69b5c42a3045ab213a66a5d377617f2
df28bcd9dcf028a3edd06b6a4efa75629ddb5d17
describe
'240408' 'info:fdaE20090919_AAABWXfileF20090919_AADUUB' 'sip-files00003.jp2'
24813b3184996e0e2f74c71cd1d0e248
9bd824ed90eeeb11e9f8eb2380addb8218ad3cdb
'2012-04-03T19:02:00-04:00'
describe
'192735' 'info:fdaE20090919_AAABWXfileF20090919_AADUUC' 'sip-files00003.jpg'
4d3bbafebe165b3cf7f1365c5f5c8589
db39c41714c6e726001504e0408e905565ee5b7c
'2012-04-03T19:01:43-04:00'
describe
'109117' 'info:fdaE20090919_AAABWXfileF20090919_AADUUD' 'sip-files00003.pdf'
2727a720502d4a6e95841329e463d5a3
dda754c5dfef824a59e747f92e24ee594d6fab29
'2012-04-03T19:02:01-04:00'
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUUD-norm-0' 'aip-filesF20090919_AADUUD-norm-0.pdf'
48c279620392bcf49e367d81b9512286
1d5e440b611127d699bf9932b2b9060ff387b025
describe
'2015-05-15T18:10:54-04:00'
normalize
'124814' 'info:fdaE20090919_AAABWXfileF20090919_AADUUE' 'sip-files00003.pro'
47cc586628a32dcde3ec42b787dd4f23
78d6dfea4850865861b7577a4cc8542b04a40c2f
'2012-04-03T19:01:18-04:00'
describe
'49309' 'info:fdaE20090919_AAABWXfileF20090919_AADUUF' 'sip-files00003.QC.jpg'
84955d77be323c587bd85dd44b5325f8
b98053d64a63251fef04d8e3e65dc59a63b66e54
'2012-04-03T19:01:26-04:00'
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUUG' 'sip-files00003.tif'
a7b1e2741bd875fbd3ab35c9cbb9c9b4
d42ae3bef896af2003fbd3b30d4b8a127d2966f1
'2012-04-03T19:01:45-04:00'
describe
Invalid DateTime length:
Invalid DateTime length
Invalid DateTime length
'4879' 'info:fdaE20090919_AAABWXfileF20090919_AADUUH' 'sip-files00003.txt'
25724e7e590f96b985fb3f4fee30528b
bebd4481e3f32c162f43d9a279ebb7a8ad3e0307
'2012-04-03T19:01:41-04:00'
describe
'11644' 'info:fdaE20090919_AAABWXfileF20090919_AADUUI' 'sip-files00003thm.jpg'
29a214a78f7ee460d848784ec8e10979
75bf59b6b5b7655c0536f5b25656f53a0ad4cd2e
describe
'262300' 'info:fdaE20090919_AAABWXfileF20090919_AADUUJ' 'sip-files00004.jp2'
12cc698f3b52cba9bfc5ddc39966ba5c
2a3b2d33d57e0296fec16ce2284b7b3bcb861bc0
'2012-04-03T19:01:54-04:00'
describe
'235129' 'info:fdaE20090919_AAABWXfileF20090919_AADUUK' 'sip-files00004.jpg'
9c49996b61f371b9beac2eee946289ea
b0716d2b9be0609131f43fbc34e71f82f4511793
'2012-04-03T19:01:49-04:00'
describe
'113562' 'info:fdaE20090919_AAABWXfileF20090919_AADUUL' 'sip-files00004.pdf'
5e0173132bfc999e033eb9bb6285c3a6
10c2c41633179eb83ed38645988d984eb44757cd
'2012-04-03T19:01:47-04:00'
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUUL-norm-0' 'aip-filesF20090919_AADUUL-norm-0.pdf'
48c279620392bcf49e367d81b9512286
1d5e440b611127d699bf9932b2b9060ff387b025
'2015-05-15T18:10:56-04:00'
describe
'2015-05-15T18:10:48-04:00'
normalize
'131847' 'info:fdaE20090919_AAABWXfileF20090919_AADUUM' 'sip-files00004.pro'
57d3c13ee6491458d942aab36c64e27c
4a4e6273da7df00a088c4146c236815964a4df1a
describe
'87696' 'info:fdaE20090919_AAABWXfileF20090919_AADUUN' 'sip-files00004.QC.jpg'
e2fd0fb0684eebee6bfe13a6bcf23eef
f34f58727ae69025e10cbbdd2b84d291b0df4a07
describe
'1071408' 'info:fdaE20090919_AAABWXfileF20090919_AADUUO' 'sip-files00004.tif'
61413443bca34018f46057d06ead4175
c4e58434b727587670b4390ad2786bdfd1a431c3
'2012-04-03T19:01:23-04:00'
describe
'5114' 'info:fdaE20090919_AAABWXfileF20090919_AADUUP' 'sip-files00004.txt'
a71f31d3116e9d5797bdc17c64e7da07
dac6d5ee31f8e784e7e54c9b5f01adeaf4cc0312
'2012-04-03T19:01:51-04:00'
describe
'47623' 'info:fdaE20090919_AAABWXfileF20090919_AADUUQ' 'sip-files00004thm.jpg'
c4c94271410736b3d5c7d1bc8e6f8f4e
0747276c761e52ecf6c8928c1bb552e8bbab3d7a
'2012-04-03T19:01:48-04:00'
describe
'237589' 'info:fdaE20090919_AAABWXfileF20090919_AADUUR' 'sip-files00005.jp2'
c6a3c8a95dbbe500c9ffde89a28b5891
cb8dd31b2bbcb5d1e56ef6f5e0b87ecc162658dc
'2012-04-03T19:02:04-04:00'
describe
'189149' 'info:fdaE20090919_AAABWXfileF20090919_AADUUS' 'sip-files00005.jpg'
49edc450fd7018157622f249f321c990
d7a9bf5808d65638b7e45fb0820e83d15ef2b8be
'2012-04-03T19:01:20-04:00'
describe
'107065' 'info:fdaE20090919_AAABWXfileF20090919_AADUUT' 'sip-files00005.pdf'
b5c4f947497abb642a6d8f966d89f606
0e309ac91646ad35341bc20e3a5b9d85d6153c8e
'2012-04-03T19:01:36-04:00'
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUUT-norm-0' 'aip-filesF20090919_AADUUT-norm-0.pdf'
48c279620392bcf49e367d81b9512286
1d5e440b611127d699bf9932b2b9060ff387b025
describe
'2015-05-15T18:10:40-04:00'
normalize
'122094' 'info:fdaE20090919_AAABWXfileF20090919_AADUUU' 'sip-files00005.pro'
400d581c2001abb2d97b024d525e3337
2370e51070dc5947f5725ca40c975beaffaa22a3
'2012-04-03T19:01:40-04:00'
describe
'48747' 'info:fdaE20090919_AAABWXfileF20090919_AADUUV' 'sip-files00005.QC.jpg'
6d89a3259f6f9b56c0920d2144389e32
8c2c0f847f8a69aea372ef5c40c7541022247f34
describe
'1031976' 'info:fdaE20090919_AAABWXfileF20090919_AADUUW' 'sip-files00005.tif'
e3418082e137b610e33983fef74c25c9
4d16aeab1af1acac10838b0379a355d7c6c436a4
describe
Invalid DateTime length:
Invalid DateTime length
Invalid DateTime length
'4812' 'info:fdaE20090919_AAABWXfileF20090919_AADUUX' 'sip-files00005.txt'
7241d4b5bf7996228816ff430b8182b7
eab20b1467a36b7211fb38bf4ca0d75bd99cf165
describe
'11797' 'info:fdaE20090919_AAABWXfileF20090919_AADUUY' 'sip-files00005thm.jpg'
ffda4f425b1124716692a3c828e90b30
f454b88c5ecec192d444dddbc77316f93c8cd921
'2012-04-03T19:02:07-04:00'
describe
'238800' 'info:fdaE20090919_AAABWXfileF20090919_AADUUZ' 'sip-files00006.jp2'
ae7ec4545939d7a0c5e60891d63c4871
683ddeef0c1334a4a5dc7a0ed5ddf42a9a724023
'2012-04-03T19:02:03-04:00'
describe
'215989' 'info:fdaE20090919_AAABWXfileF20090919_AADUVA' 'sip-files00006.jpg'
37d41a3302318f2dc6e80154b2a0f158
70d54ca771868d8a000419d360d71a2c69831fd7
describe
'103597' 'info:fdaE20090919_AAABWXfileF20090919_AADUVB' 'sip-files00006.pdf'
7d5a9a7efcec3034e238065c21520b8e
db2fa166a2ff4e50d815aa5a9d9cfd0472bc32c4
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUVB-norm-0' 'aip-filesF20090919_AADUVB-norm-0.pdf'
48c279620392bcf49e367d81b9512286
1d5e440b611127d699bf9932b2b9060ff387b025
describe
'2015-05-15T18:10:36-04:00'
normalize
'120021' 'info:fdaE20090919_AAABWXfileF20090919_AADUVC' 'sip-files00006.pro'
44fe27f59572a61dd9fe66ba7d7aa6dc
947704a45bb6814826db307011b97c30511852bc
'2012-04-03T19:01:28-04:00'
describe
'81324' 'info:fdaE20090919_AAABWXfileF20090919_AADUVD' 'sip-files00006.QC.jpg'
1087ac1963bb5a72b93e5a62270ea1ac
c87b454db910b5fab77b736f68f299b7f15939d9
'2012-04-03T19:01:42-04:00'
describe
'1065168' 'info:fdaE20090919_AAABWXfileF20090919_AADUVE' 'sip-files00006.tif'
878389e8a9ba639608da1ec0312aa2fe
b614f66a265014d65d36997093b16508aa624427
describe
'4772' 'info:fdaE20090919_AAABWXfileF20090919_AADUVF' 'sip-files00006.txt'
e107131d907a80c966d38b8a1ac57660
72bc2e73bc6a8af6e9de079131bed4afe0f96a43
'2012-04-03T19:02:02-04:00'
describe
'44742' 'info:fdaE20090919_AAABWXfileF20090919_AADUVG' 'sip-files00006thm.jpg'
ed37ecef90c1da914683949d17fa371e
267d9388fbd655b3ab085cb52e027cc11fb66a80
describe
'94406' 'info:fdaE20090919_AAABWXfileF20090919_AADUVH' 'sip-files00007.jp2'
c2b4302cd87499de7e03a122e8138f5f
fbca445962c408c48d41a265d25040dcad2a2fb4
'2012-04-03T19:01:57-04:00'
describe
'80136' 'info:fdaE20090919_AAABWXfileF20090919_AADUVI' 'sip-files00007.jpg'
3192373e08052ce91f0eccd5658d4702
5c0468b17351882f3679b8699641fe2962924358
describe
'42835' 'info:fdaE20090919_AAABWXfileF20090919_AADUVJ' 'sip-files00007.pdf'
ca6e785a9d2d864a3ab0bb73e46a12c9
fbf7d22dec31b6a720d51ce92252c107933f20e4
describe
'info:fdaE20090919_AAABWXfileF20090919_AADUVJ-norm-0' 'aip-filesF20090919_AADUVJ-norm-0.pdf'
48c279620392bcf49e367d81b9512286
1d5e440b611127d699bf9932b2b9060ff387b025
describe
'2015-05-15T18:10:51-04:00'
normalize
'44539' 'info:fdaE20090919_AAABWXfileF20090919_AADUVK' 'sip-files00007.pro'
39469006abc4c1dc4cf7f374682c1046
fa52cca003f73874af80ca8dcb56f1984dc40c37
describe
'22079' 'info:fdaE20090919_AAABWXfileF20090919_AADUVL' 'sip-files00007.QC.jpg'
18ec552d8ec784e71285a2e14f4e047a
2e3e7b5608fea535f9f279557562453d123379de
describe
'1029943' 'info:fdaE20090919_AAABWXfileF20090919_AADUVM' 'sip-files00007.tif'
659a32c97c1ee8e36a567f7408bc1cc7
884cefd600d9797244128795cf56e3a68fbd278c
describe
Invalid DateTime length:
Invalid DateTime length
Invalid DateTime length
'1874' 'info:fdaE20090919_AAABWXfileF20090919_AADUVN' 'sip-files00007.txt'
6922a8ed2d6c4c82e357845b0173fe22
ec5062eae6c03fd7f113ba8364a1cd25c343ccff
describe
'5769' 'info:fdaE20090919_AAABWXfileF20090919_AADUVO' 'sip-files00007thm.jpg'
5447f5b91fbf99c171941658ad40429e
cf7f5d055480c162c3b76b1799dc16a52454e9d2
describe
'19699' 'info:fdaE20090919_AAABWXfileF20090919_AADUVP' 'sip-filesUF00008572_00001.mets'
c1e6895772d609606a5d78e94117e251
641e6837c473a74950133f6a6b6d67e05da1b81b
'2012-04-03T19:01:46-04:00'
describe
TargetNamespace.1: Expecting namespace 'http://www.uflib.ufl.edu/digital/metadata/ufdc2/', but the target namespace of the schema document is 'http://digital.uflib.ufl.edu/metadata/ufdc2/'.
'2015-05-15T18:10:59-04:00' 'mixed'
xml resolution
http://www.uflib.ufl.edu/digital/metadata/ufdc2/ufdc2.xsd
BROKEN_LINK schema http://www.uflib.ufl.edu/digital/metadata/ufdc2/ufdc2.xsd
The element type "div" must be terminated by the matching end-tag "
".
TargetNamespace.1: Expecting namespace 'http://www.uflib.ufl.edu/digital/metadata/ufdc2/', but the target namespace of the schema document is 'http://digital.uflib.ufl.edu/metadata/ufdc2/'.
'23765' 'info:fdaE20090919_AAABWXfileF20090919_AADUVS' 'sip-filesUF00008572_00001.xml'
3ee77b88b9e7a574fd20adbda1934216
497deca27671078a87e3009a061699c805ec99de
describe
TargetNamespace.1: Expecting namespace 'http://www.uflib.ufl.edu/digital/metadata/ufdc2/', but the target namespace of the schema document is 'http://digital.uflib.ufl.edu/metadata/ufdc2/'.
'2015-05-15T18:10:58-04:00'
xml resolution
http://www.uflib.ufl.edu/digital/metadata/ufdc2/ufdc2.xsd
http://www.uflib.ufl.edu/digital/metadata/ufdc2/ufdc2.xsd
The element type "div" must be terminated by the matching end-tag "".
TargetNamespace.1: Expecting namespace 'http://www.uflib.ufl.edu/digital/metadata/ufdc2/', but the target namespace of the schema document is 'http://digital.uflib.ufl.edu/metadata/ufdc2/'.



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Agricultural Chemical Drift and Its Control Page 7 droplets. Request a droplet spectrum data sheet from the manufacturer that gives information about the percentage of the droplets that are smaller than 150 micrometers. Use nozzles with the smallest portion below this size. * Use the lowest pressure possible that will give adequate coverage and control to limit the number of drift-prone droplets. * Make the application at the minimum height that provides a uniform spray pattern. * Shut off sprayers when turning at the ends of the rows. * Spray early in the morning, late in the evening, or at night, whenever possible, to avoid killing honey bees. ADDITIONAL RECOMMENDATIONS FOR AERIAL APPLICATIONS * Orient the nozzles straight back to minimize small droplet formation due to wind shear. * Limit the boom length to 75% of the wingspan of the aircraft in order to prevent small droplets from becoming entrained in the wing tip vortices and contributing to drift problems. * Limit aircraft speed when applying chemicals that crops in neighboring nontarget fields are particularly sensitive to. Modern turbine powered aircraft capable of flying in the 150 to 160 mph range will create more small driftprone droplets at these speeds. * Dress the ends of a field with a couple of passes, so that the sprayer does not have to be turned on before the aircraft is level at the beginning of a pass or left on after pulling up at the end of a pass. * If a customer wants a field treated "now" when conditions indicate a high potential for a drift problem, explain to the customer why it would be unwise to make the application under the existing conditions.



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Agricultural Chemical Drift and Its Control Page 5 type of chemical has been limited severely by the major crops, has decreased considerably), the number Environmental Protection Agency. The chlorinated of drift-related problems could increase. Many people hydrocarbons (DDT is the most renowned chemical are moving to Florida and developments are being in this group) are an example of a pesticide group that built ever closer to long standing agricultural remained in the environment for years. These operations. Many of these people are terrified at the chemicals were very effective pesticides with low thought of an agricultural pesticide, regardless of the mammalian toxicity, but they accumulated over time level of residue, drifting into their residential area. in the environment. DDT caused the egg shells of birds of prey like the bald eagle to be very thin and A large portion of Florida residents pay to have they often cracked before the young eaglets hatched. pest control operators apply levels of pesticides that have been scientifically tested for efficacy and safety IPM HAS REDUCED RELIANCE ON inside their house and in their yard. If the same level CHEMICALS of residue of the chemical occurred in the yard because of spray drifting from an agricultural pest In Florida, there is probably less drift of chemicals control operation, it would probably be a matter of into nontarget areas today than in the past because great concern to residents in the area. This-is growers are not relying solely on chemicals to control somewhat perplexing, but understandable. The benefit pests. Growers are using "Integrated Pest received from the pest control operator's application Management (IPM)" in their fight against pests. IPM is the obvious absence of roaches, fleas, chinch bugs is an ecological approach to pest management that or whatever pest that plagues the homeowner. People often provides economical, long-term protection from do not see the benefit of agricultural pest control "first pest damage or competition. Concern about pesticides hand". Even though the public is told that agricultural in the environment and their potential harm to users pesticide use makes for high quality, low cost food, the and the public spurred the interest in IPM. The benefit is not as obvious as the absence of household practitioners of IPM use a combination of pest control pests. methods to prevent their crops from suffering economic losses. A few examples of nonchemical pest Another reason for the strong potential for more control methods used by growers are: (1) planting drift problems in the future, in spite of possibly less crop varieties that have natural resistance to pests, (2) drift, is the relatively new field of Environmental Law crop rotations that have proven to be helpful in coupled with equipment capable of detecting the reducing pest problems, and (3) chopping and burying presence of extremely low levels of any substance. residues from the previous year's crop. WHAT CAUSES DRIFT? IPM does not exclude the use of chemical control methods, but chemical use is reserved as the last line The distance that a droplet moves laterally when of defense in the growers' battle against pests. released in air depends on the time the droplet is Sometime data collected in the field show that the airborne and the average horizontal velocity of the pest numbers are high enough to warrant a chemical droplet during this time period. The distance can be application to avert serious economic losses in spite calculated with the equation below: of the grower using all of the best nonchemical measures to avoid pest problems. When the decision Drift Distance = suspension time x average to apply a chemical is made, growers using IPM try to horizontal velocity choose a chemical that will kill the target pest while sparing many of the beneficial insects that prey on This equation is simple enough, if you know the various pests in the field. Preserving beneficial insects time that the droplet is suspended in the air and its can prevent or at least delay having to apply chemicals average horizontal velocity. However, determining in the future. either the suspension time or the average horizontal velocity of small droplets (100-150 micrometers or DRIFT WILL PROBABLY DECREASE WHILE less) is virtually impossible because they are DRIFT PROBLEMS INCREASE dependent on weather. Even though the application of agricultural pesticides is not increasing in Florida because of the use of IPM (pesticide use in citrus, one of Florida's



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I o Circular 1105 11 5 UNIVERSITY OF June 1993 FLORIDA Florida Cooperative Extension Service Agricultural Chemical Drift and Its Control' Richard P. Cromwell 2 INTRODUCTION but they were either mixing or loading the concentrated chemical and were not using procedures Drift is the airborne movement of particles into recommended on the product label. nontarget areas. It is both undesirable and, to a degree, unavoidable. Drift problems can be minimized Although hazardous pesticide residues on produce by understanding what causes it and following grown in the United States is a rare occurrence, it is recommended procedures for limiting it. still a major public concern. A 1984 consumer survey showed that of all the possible harmful products found The fear of chemical drift is out of proportion to in food, the public worried most about pesticide the threat that it poses to people and the environment, residues. Because the public perceives that pesticides This statement is supported by a video tape, "Big in our food supply is a major problem, applicators of Fears, Little Risks," presented by The American pesticidal chemicals should apply them wisely to Council on Science and Health. In this video tape, minimize drift and to avoid drift problems. Some Dr. Bruce Ames, a scientist at the University of recommended procedures for minimizing drift are California, Berkeley and the developer of the Ames presented in this publication. test, a widely used test to determine the carcinogenic nature of chemicals, states that the low levels of Note: The remainder of this publication will primarily chemicals in the environment are much less of a threat refer to pesticidal particles as droplets because the to human health than life-style related factors such as majority of pesticides are applied as sprays. However, smoking, diet, sexual behavior, and others. small particles of dry material are also prone to drift. Pesticidal dusts were once the most common What about the threat of chemicals that drift from formulation used in agriculture in the late 1940's when treated fields and settle directly onto unsuspecting the use of synthetic pesticides became a common people? Workers in adjacent fields have been practice. Dusts are seldom used in agriculture today accidently sprayed by drift and received a dose because they are so prone to drift from the target sufficient to cause serious illness. However, the safety area. specialist at both the University of Florida in Gainesville, FL, and the University of California in Davis, CA, two of the more important agricultural states, do not recall any documented cases of a person 's death being caused by spray drift. People have died from accidental poisoning by agricultural chemicals, 1. This document is Circular 1105, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: June 1993. 2. Richard P. Cromwell is Associate Professor and Extension Specialist, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611. The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida I John T. Woeste, Dean U,:;'-'.SITY OF FLOIA P, i.-,-ftuS


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Agricultural Chemical Drift and Its Control Page 6 Large Droplets Drift Very Little RECOMMENDATIONS FOR REDUCING DRIFT AND DRIFT PROBLEMS The time that a large droplet is suspended in the air depends on the height from which it is released * Nozzles should be used that produce as large of and its average velocity in the vertical direction. A a droplet spectrum as possible while yielding large droplet released in air will fall at an increasing adequate plant coverage and pest control. Large velocity until the droplet's weight is equal to the nozzle orifices and low spray pressure creates a upward force on the droplet due to air friction. When large droplet spectrum. It may be necessary to these two forces are equal, the object will fall at a apply higher than normal amounts of diluted spray constant velocity known as the terminal or settling per acre when using large droplets to avoid drift velocity.The terminal velocity of a large droplet is in order to get adequate coverage. relatively high because it takes high velocities to generate enough friction force to balance the object's * Do not make applications during temperature weight. Depending on the height from which a large inversions. An inversion is a stable atmospheric droplet is released, it could strike the ground before condition characterized by an increase in air reaching its terminal velocity. Large droplets drift temperature with an increase in height above the very little primarily because their suspension time is ground until at some height a barrier of cold air small. is met. Use a column of smoke near the application site to check for an inversion. The Small Droplets Can Drift For Great Distances smoke will rise to the level of the cold air barrier and will then move laterally below it. The settling velocity of a small droplet is very low because its weight is low. If the droplet is suspended * Usually less material will drift from the target field in air that has an updraft velocity greater than the during an inversion, but the material that does settling velocity of the droplet in still air, the droplet leave the target field remains in a more will actually rise rather than fall. concentrated cloud and the level of residue that settles onto nontarget areas will be higher than The weight of most spray droplets diminishes with usual. Even though the amount of chemical that time because the volatile portion of the spray droplet drifts from the target area during an inversion is evaporates. Evaporation reduces the weight of small often less, the potential for a drift problem can be droplets more rapidly than larger ones because they greater because the small droplets are not lofted have more surface area relative to their mass. into the upper atmosphere, diluted and spread Therefore, a small particle that consists primarily of over a large area. water is drift-prone initially and becomes even more drift-prone with time. * Make applications when the wind is blowing away from any highly sensitive nontarget areas and the Because the vertical velocity of small droplets can wind velocity should range between 3 to 10 mph. be either down or up and the wind direction can Extremely low winds are avoided because they change during the extended time that a small droplet indicate inversion conditions and winds above 10 is suspended, it is virtually impossible to predict the mph are avoided because relatively large droplets distance that the droplet will drift. Neither the can be transported into neighboring fields. suspension time nor the average horizontal velocity can be predicted with any degree of certainty. A small * Leave a buffer zone of approximately 300 feet droplet will either completely vaporize or the between the treated field and any particularly nonvolatile portion of the droplet (many spray sensitive areas. Buffer zones will avoid mixtures contain some small amount of nonvolatile contamination of neighboring areas by the oil) will eventually settle to the ground due to the ever displacement of relatively large spray droplets. present force of gravity. The air mass carrying the However, buffer zones will not effectively droplet must remain calm for a relatively long time in eliminate low level contamination of distant areas order for the droplet to settle out. by the small droplets formed by all commercially available nozzles. *The nozzles must provide adequate coverage and pest control while minimizing small, drift prone



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Agricultural Chemical Drift and Its Control Page 4 adjacent field that would be wide enough to avoid the Environmental Protection Agency (EPA), the contaminating the nontarget field. agency that regulates agricultural pesticides. LONG RANGE DRIFT IS NOT PREDICTABLE DRIFT CAN OCCUR AT THE TIME OF APPLICATION OR LATER Long range drift of small droplets is not predictable because a small droplet does not always Chemicals can drift from the target area and cause fall while suspended in air. Air can have a vertical a drift problem at the time of the application or at velocity component which is generally upward during some time after the application. Drift that occurs the middle of the day when the warm air at ground after the application are caused by: (1) having the dry level is displaced by the cooler, heavier air above it. residue of a wettable powder applied as a spray blown The vertical updraft can cause a friction force on a into an adjacent area after the water carrier small droplet that is greater than the droplet's weight. evaporates, (2) having chemical vapors transported When the upward force exceeds the droplet's weight, downwind or (3) having high winds blow pesticidethe droplet will rise rather than fall. To make treated soil and plant particles from the target field matters worse, the weight of a spray droplet reduces into a neighboring area some time after the chemical over time because water (most spray droplets are was applied. Contamination resulting from a chemical predominantly water) in the droplet evaporates. being transported into nontarget areas hours or even days after application are an oddity. Very few of the A small droplet will remain airborne until the air problems caused by drift have resulted from "post mass transporting the droplet is calm long enough to application" drift. This publication is primarily allow the small downward force of gravity to cause it concerned with the drift of particles that begin their to settle to the ground. Because weather is flight into neighboring areas at the time of application. unpredictable, accurately predicting where a small This is the type of drift that is most prevalent and airborne droplet will eventually land is essentially deserves most of the attention. impossible. The location is largely a matter of chance. There are computer models used to determine where DRIFT AND DRIFT PROBLEMS droplets will settle under given environmental conditions. These models predict the paths taken by There is a difference between drift and drift the larger droplets, but are not very accurate when problems. Virtually all spray applications result in predicting where the small droplets settle out. These some small amount of spray drifting beyond the programs are useful for determining how wide a buffer immediate target area. This does not mean that the zone should be to keep swath displacement from drift has created a "problem". causing problems in nearby fields. Fortunately the residue level that accumulates because of long range The chemical may drift from the target area onto drift is usually very low and often undetectable. an area totally within the holdings of the person applying it. This person probably would not consider Whether the low level of chemical that results the drift to be a problem. If the chemical drifts onto from long range drift constitutes a problem depends a nontarget area not totally within the holdings of the on who is asked. There are some people who feel person applying it and the residue level is too small to that chemicals settling on nontarget areas at any level cause an immediate effect (offensive odor, illness of is a problem. If the only acceptable level of drift into residents, damage to plants, etc.), there probably will nontarget areas was zero, all spray operations would not be a problem caused by the drift. Chemicals used have to be shut down along with many industrial in today's agriculture are less likely to accumulate in operations. There is no such thing as "zero drift" for the soil or water because the pesticides that are used any operation where small particles are released into are degraded by the effects of sunlight and soil the atmosphere. Even large objects are displaced microorganisms. Rapid degradation without some small amount when falling in air that has an accumulation of a chemical or its breakdown products horizontal wind velocity. However, it is possible to is a major consideration in determining whether the keep drift to a such a low level that the benefits from chemical can be used as a pesticide. applying a chemical exceed the potential risks in the minds of most rational people. If this were not so, the For example, chemicals that remain as toxins in application of the chemical would not be allowed by the environment for a long time (years in some cases) are known as persistent pesticides and the use of this