Contents
Weather-Wise Application ..................................................................................................................... 1
Goals of This Chapter .......................................................................... Error! Bookmark not defined.
Avoid High Temperature and Low Humidity Conditions ................................................................... 1
Avoid Windy Days .............................................................................................................................. 2
Other Wind and Temperature Considerations .................................................................................. 2
Avoid Application Just Before Rains................................................................................................... 2
Consider Early Morning or Evening Application ................................................................................ 3
20 Weather-Wise Application
Weather-wise application can reduce pesticide hazard to the environment. A good applicator
carefully checks the weather conditions before beginning spray procedures. Not only do a few simple
precautions protect the environment, but in terms of dollars and cents they aid the applicator.
Pesticides which do not reach or remain on the target areas are wasted. More pesticide, time, and
money must be used to control the pests in the target area.
Key points on this page
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inversion in regard to pesticide application.
Avoid High Temperature and Low Humidity Conditions
Learn the role that weather
conditions can play in both
helping and hindering the
applicator.
Understand the hazards of
windy day application and who
is legally responsible for
mistakes.
Learn the advantages of early
morning or evening application.
Understand the roles of
humidity and temperature
Temperature and humidity affect pesticide drift. High temperature and low humidity increase the
rate of evaporation of the pesticide. Small droplets that completely evaporate leave pesticide particles
in the air that may be carried several miles away from the treatment area (vapor drift).
Avoid Windy Days
High winds increase drift and result in the loss of pesticide from treated areas. Drifting pesticides
increase the possibility of injury to wildlife, pollinators, and domestic animals. They may settle on
forage, pasture or wildlife areas or contaminate water. Pesticide application on quiet days reduces the
inhalation and contact hazard to the applicator and the bystander. Drift onto sensitive crop areas can
also be avoided in this way. The applicator is legally responsible for any injury or money loss due to
pesticide drift onto non-target areas. Don't take a chance by spraying in the wind.
Other Wind and Temperature Considerations
The drift of pesticides is also affected by the air turbulence. The air turbulence is determined by the
difference between the temperature at ground level and the temperature of the air above it. Normal
weather conditions cause heating of the soil. If the air just above the soil is warmer than the air aloft,
upward air currents begin. The larger the temperature differences between air above the soil surface
and the air aloft, the stronger the air currents. These air currents could carry spray droplets and
pesticide particles a considerable distance away from the treatment area. Do not apply pesticides when
such turbulent conditions exist.
An inversion occurs when the air near the soil surface is cooler than the air above it. The warm air
forms a cap that blocks upward air movement that would otherwise help disperse the chemicals. Wind
can aid in air mixing and reduce inversion conditions. However, low wind conditions during inversion
conditions may cause small spray drops to remain suspended in the air. The droplets will eventually
move out of the treatment area as a concentrated cloud. Smoke can be used as a good indicator of an
inversion condition. Do not apply pesticides when inversion conditions exist.
Avoid Application Just Before Rains
Spray applications should not be made just before a rain, because the pesticide washes off and the
pests are not controlled. Rains cause runoff and tend to wash the pesticide away from the target areas.
The runoff can carry the pesticide into sensitive areas where crops or wildlife could be injured. Runoff
can also reach surface waters such as farm ponds, streams and waterways. Ultimately, this can cause
contamination, fish kills, and injury to domestic animals.
Consider Early Morning or Evening Application
Wind speed is usually lowest and humidity higher at these times of the day, thus drift hazard is
greatly reduced. Children and domestic animals are less likely to be in sprayed areas during these hours.
Avoiding full daylight hours lowers the contact danger to wildlife such as birds, mammals, and
pollinators, who often visit croplands during the day.
Weather-Wise Application – Self Study Questions
1.
Can weather conditions actually aid in reducing pesticide pollution?
2.
Can weather-wise application aid the applicator economically?
3.
Why should a careful applicator avoid applying pesticides on windy days?
4.
Why are drifting pesticides more hazardous?
5.
Does windy day application pose increased hazard for the applicator and the
bystander?
6.
If a pesticide drifts onto non-target areas resulting in injury or economic loss,
who is legally responsible?
7.
Why must spray applications dry onto a surface before a rain?
8.
What harm can pesticide runoff do?
9.
What are two advantages of early morning or evening application?
10.
What weather factors affect drift?
11.
When does an inversion occur?
Answers to Self Study Questions -- Weather-Wise Application
1.
Yes. Wind can aid in reducing pollution caused by an inversion.
2.
Yes. Drift wastes pesticides and money.
3.
Wind causes pesticide particles to drift off target.
4.
Drifting pesticides are out of the applicator's control; therefore they are able to
land and damage non-target organisms at random.
5.
Yes. Quiet day application reduces the inhalation and contact hazard to the
applicator and the bystander.
6.
The applicator is legally responsible for any injury or money loss due to pesticide
drift.
7.
Rains cause pesticides to run off target.
8.
Pesticide runoff can cause injury to crops, wildlife, or contaminate surface
waters.
9.
Wind speed is lowest. Children and animals are not likely to be present.
10.
Wind, high temperatures, and humidity.
11.
Inversions occur when the air near the soil surface is cooler than the air above it.
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Disclaimer: Please read the pesticide label prior to use. The information contained at this web site
is not a substitute for a pesticide label. Trade names used herein are for convenience only; no
endorsement of products is intended, nor is criticism of unnamed products implied. Most of this
information is historical in nature and may no longer be applicable.
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