Southeastern U.S. Vegetable Crop Handbook - 2022 - 146

Pesticides that are highly soluble in water have a higher
potential for contaminating groundwater than those that are less
soluble. The water solubility of a chemical indicates how much
chemical will dissolve in water and is measured in parts per million
(ppm). Those chemicals with a water solubility greater than
30 ppm may create problems. Be sure to read the Environmental
Precautions on each pesticide label.
A chemical's ability to adhere to soil particles plays an important
role. Chemicals with a high affinity for soil adsorption are
less likely to reach the aquifer. Adsorption is also affected by the
amount of organic matter in the soil. Soils with high organic matter
content are less vulnerable than those with low organic matter
content.
Finally, how persistent a chemical is in the environment may
affect its ability to reach groundwater. Those that persist for a
long time may be more likely to cause contamination than materials
that breakdown quickly. Persistence is measured by the time
it takes half of a given pesticide to degrade. This is called the
chemical's half-life. Chemicals with an overall estimated half-life
longer than 3 weeks pose a threat to groundwater.
HOW TO PREVENT CONTAMINATION OF GROUND WATER
Examine the chemical properties of the pesticides used. If
using materials that persist for long periods of time, are very water
soluble, or are not tightly held by the soil, then your groundwater
may become contaminated. Another material may be
selected that has a shorter persistence, lower water solubility, or
higher potential for soil adsorption. The following chart assists
with these decisions.
1. Determine the local soil and geologic circumstances. If
in an area with a shallow water table or the soil is low
in organic matter or sandy in nature, there is a greater
risk of contaminating your groundwater. In these cases,
choose a pesticide that has a low water solubility and is
not persistent.
2. Evaluate management practices. These practices maybe
the most important factors in determining the risk
of contaminating groundwater. If the same materials
are used year after year, or many times a season, the
potential for contamination can be increased due to the
amount of pesticide in the soil. The timing of pesticide
applications has an effect on groundwater contamination.
If applications during periods of high rainfall
or heavy irriga tion are made, it is more likely that
contamination may occur. Also, the water table in the
spring may be higher than at other times. Early season
applications, therefore, may pose a greater chance for
groundwater contamination.
3. The method of application may have an effect. Direct
injection, incorporation, and chemigation all increase
the chance of contamination. If using these techniques,
be sure to follow the procedures listed on the material's
label.
4. The location of wells can be important. If the sprayer
loading area or pesticide storage building is too close
to a well, the risk of contamination may be greater.
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Wells should be located a minimum distance from all
pesticide storage and loading areas. This distance differs
between states but is generally between 50 and 100
ft. In the event of an accident, this distance should prevent
contamination. This minimum distance should also
be followed for field irrigation wells. If they are too
close to application areas, contamination might occur.
5. Check the condition of any wells in the vicinity of
sprayer loading areas, pesticide storage areas, or field
applications. If they have cracked casings trouble is
being invited. Cracks in a well casing provide a direct
point of entry for pesticide-contaminated water that is
in the soil.
6. Use some type of anti back-flow device in any system
used for chemigation or to fill the sprayer with water.
In the event of a pump shutoff or other failure, if any
back-flow into the water system occurs, these devices
will prevent pesticides from entering the well. Many
state laws require that anti back-flow devices be placed
on all sprayer water intake systems prior to the water
entering the tank. The use of an air gap only is no longer
acceptable in some states.
7. Care and maintenance of equipment is also an important
consideration. If the equipment does not function
properly, over-delivery may occur, which increases the
chance of groundwater contamination. Prior to the beginning
of the season, inspect all of the working parts
of the sprayer or chemigation system. Check the pump
to ensure that it is working properly. For both sprayers
and chemigation systems, check the water lines for
clogs and leaks. For sprayers, check the nozzles for
wear and clogs. Clogged, leaking, or worn lines and
nozzles can cause pesticides to be delivered in too high
an amount or into unwanted areas. Be sure to calibrate
equipment. Uncalibrated equipment can cause over-delivery
as well. Equipment should be calibrated at the
beginning of the season, periodically during the remainder
of the season, and any time changes or adjustments
are made to the equipment.
8. Apply materials only when needed. The use of pesticides,
when not needed, can increase the threat of
contamination. Check irrigation practices as well. Do
not irrigate immediately after a pesticide application,
unless required by a pesticide's label. The increased
water content in the soil might speed up the downward
movement of a pesticide.
9. One of the best ways to reduce indirect or direct runoff
would be to only purchase and use what is needed to
completed a treatment. Runoff and poisoning can stem
from not properly disposing of extra pesticides.
REMEMBER, GROUNDWATER
MUST BE PROTECTED.
2022 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2022

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