What Happens to Pesticides Applied to Golf Courses?
In the late 1980's, golf was faced with a dilemma. On one
hand, regulatory agencies responding to public concern routinely
initiated environmental monitoring programs of ground and surface
water. On the other hand, very little public information was
available on the behavior and fate of pesticides and fertilizers
applied to turfgrass. Probing, sometimes over-zealous federal and
state regulators looking for non-point source polluters raised
concerns about a recreational game that had relied on the
integrity of chemical companies and the EPA to provide products
and guidelines that protect the environment. There were lots of
questions but few answers.
The game of golf needed answers to environmental questions, and
the USGA wanted these answers based on scientific facts, not
emotions. In 1991 the USGA initiated a three-year study of the
fate of pesticides and fertilizers applied under golf course
conditions. This article first briefly describes what is known
about the fate of chemicals used on golf courses and provides
some supporting documentation to help choose a pesticide.
Highlights of the research projects then are summarized, but the
articles should be read to learn more about the particulars of
each research project.
Do golf courses pollute the environment? No, they do not. At
least not to the extent that critics state in undocumented media
hype. Golf course superintendents apply pesticides and
fertilizers to the course, and depending on an array of
processes, these chemicals break down into by-products that are
In general, there are six processes that influence the fate of
chemical products applied to golf courses.
- Solubilization by water.
- Sorption by soil mineral and organic matter.
- Degradation by soil microorganisms.
- Chemical degradation and photo-decomposition.
- Volatilization and evaporation.
- Plant uptake.
The relative importance of each process is controlled by the
chemistry of the pesticide or fertilizer and environmental
variables such as temperature, water content, and soil type.
The extent to which a chemical will dissolve in a liquid is
referred to as solubility. Although water solubility is usually a
good indicator of the mobility of a pesticide in soils, it is not
necessarily the best criterium. In addition to pesticide
solubility, the pesticide's affinity to adhere to soils or
sorption must be considered.
The tendency of a pesticide to leach or run off is strongly
dependent upon the interaction of the pesticide with solids
within the soil. The word sorption is a term that includes the
process of adsorption and absorption. Adsorption refers to the
binding of a pesticide to the surface of a soil particle.
Absorption implies that the pesticide penetrates into a soil
particle. The adsorbed or absorbed pesticide is often referred to
as bound residue and is generally unavailable for microbial
degradation or pest control.
Factors that contribute to sorption of pesticides on soil
materials include: a) chemical and physical characteristics of
the pesticide; b) soil composition; and c) the nature of the soil
solution. In general, sandy soils offer little in the way of
sorptive surfaces. Soils containing greater amounts of silt, clay
and organic matter provides a richly sorptive environment for
Adsorption of pesticides is affected by the partition coefficient
which is reported as Kd or, more accurately, as Koc. For example,
a Koc of less than 300 to 500 is considered low.
Pesticides are broken down by microorganisms in the soil in a
series of steps that eventually lead to the production of CO2
(carbon dioxide), H2O (water) and some inorganic products (i.e.,
nitrogen, phosphorus, sulfur, etc.). Microbial degradation may be
either direct or indirect. Some pesticides are directly utilized
as a food source by microorganisms. In most cases, though,
indirect microbial degradation of pesticides occurs though
passive consumption along with other food sources in the soil.
Regardless, microbial degradation is a biological process whereby
microorganisms transform the original compound into one or more
new compounds with different chemical and physical properties
that behave differently in the environment.
Degradation rates are influenced by factors such as: pesticide
concentration, temperature, soil water content, pH, oxygen
status, prior pesticide use, soil fertility, and microbial
populations. These factors change dramatically with soil depth,
and microbial degradation is greatly reduced as pesticides
migrate below the soil surface.
Persistence of a pesticide is expressed as the term half-life
(DT50), which is defined as the time required for 50 percent of
the original pesticide to break down into other products.
Half-life values are commonly determined in the laboratory under
uniform conditions. On the golf course, soil temperature, organic
carbon and moisture content change constantly. These and other
factors can dramatically influence the rate of degradation.
Consequently, half-life values should be considered as guidelines
rather than absolute values.
Chemical degradation is similar to microbial degradation except
that the breakdown of the pesticide into other compounds is not
achieved by microbial activity. The major chemical reactions such
as hydrolysis, oxidation, and reduction are the same.
Photochemical degradation is a different breakdown process that
can influence the fate of pesticides. It was the combination of
chemical, biological, and photochemical breakdown processes under
field conditions that was the focus of the USGA sponsored
Volatilization is the process by which chemicals are transformed
from a solid or liquid into a gas, and is usually expressed in
units of vapor pressure. Pesticide volatilization increases as
the vapor pressure increases. As temperature increases, so does
vapor pressure and the chance for volatilization loss.
Volatilization losses generally are lower following a late
afternoon or an early evening pesticide application than in the
late morning or early afternoon, when temperatures are
increasing. Volatilization also increases with air movement, and
losses can be greater from unprotected areas than from areas with
windbreaks. Immediate irrigation is usually recommended to reduce
the loss of highly volatile pesticides.
Plants can directly absorb pesticides or influence pesticide fate
by altering the flow of water in the root zone. Turfgrasses with
higher rates of transpiration can reduce the leaching of water
soluble pesticides. In situations where the turf is not actively
growing, or where root systems are not well developed, pesticides
are more likely to migrate deeper into the soil profile with
A primary concern when applying pesticides is to determine if the
application site is vulnerable to ground or surface water
contamination (See Tables 1 and 2). In most cases, level areas
away from surface waters (rivers, lakes, or wetlands) will not be
prone to pesticide runoff and if the depth to groundwater is
greater than 50 feet on fine-textured soils, the chances for deep
percolation of pesticides is greatly reduced. More attention to
the pesticide's characteristics is needed when applications
are made to sandy soils with little organic matter, or sloped
areas with thin turf and low infiltration rates.
Parameter Value or Range Indicating Potential for
||Greater than 20
||Less than 5, usually
less than 1
||Less than 300 to
||Less than 102 atm m3
||Greater than 175
||Greater than 7
||Greater than 21
From EPA 1988 as reported by Balogh and Walker, 1992.
The most important thing a golf course superintendent can do when
applying pesticides is to read and follow the label directions.
From planning and preparation to storage and disposal, following
label directions will significantly reduce the risks of
contaminating our water resources. When possible, select a
pesticide that poses the least threat of rapid leaching and
runoff and is relatively non-persistent.
This is only a very brief overview of the processes that affect
what happens to pesticides and nutrients in the environment. The
rest of this issue of the Green Section Record is devoted to the
USGA sponsored environmental research projects, which were
conducted from 1991 through 1994. Compared to agricultural crops,
the results not only build on what is known about pesticide and
nutrient fate, and often show that turfgrass systems:
- reduce runoff
- increase adsorption on leaves, thatch and soil organic
- maintain high microbial and chemical degradation rates
- reduce percolation due to an extensive root system, greater
plant uptake and high transpiration rates.
These results reinforce the view that turfgrass areas generally
rank second only to undisturbed forests in their ability to
prevent pesticides and nutrients from reaching ground and surface
Highlights from the USGA-sponsored environmental research
University of Nebraska, Dr. Garald Horst
- After 16 weeks under golf course fairway management
conditions, detectable residues of isazofos, metalaxyl,
chlorpyrifos and pendimethalin pesticides found in soil, thatch
and verdure were 1% or less of the total application
- The average DT90 (days to 90% degradation) of the four
applied pesticides was 2 months in fairway-managed turf/soil.
Thatch played a significant role in pesticide adsorption and
Iowa State University, Dr. Nick Christians
- Pesticides and fertilizers applied to Kentucky bluegrass
have the potential to leach through a 20-inch soil profile if
- Pesticide and fertilizer leaching can be greatly reduced
during the four weeks after a pesticide or fertilizer
application by irrigating lightly and more frequently, rather
than heavily and less frequently.
- The thatch layer in a mature turf significantly decreases
the amount of pesticides from leaching into the soil
University of Georgia, Dr. Al Smith
- Data from research on simulated putting greens indicated
that the concentration of 2,4-D, mecoprop, dithiopyr, and
dicamba in soil leachate was below 4 ppb (parts per billion).
According to a leaching prediction model for agriculture
(GLEAMS), this leachate should have been 50 to 60 ppb, a
significantly higher number. This indicates that current
prediction models overestimate the potential leaching of
pesticides through turfgrass systems.
- Less than 0.5% of the applied 2,4-D, mecoprop, dithiopyr
and dicamba was found in the leachate from the simulated USGA
putting greens over a 10-week period.
- No chlorpyrifos or OH-chlorpyrifos (first order metabolite)
was detected in the leachate from the simulated putting greens
in the greenhouse or field evaluations.
- Small quantities of chlorthalonil and OH-chlorthalonil were
found to leach through the greens. However, the amount was less
than 0.2% of the total applied.
- Data from fairway runoff plots with a 5 degree slope
indicate that there is a potential for small quantities of
2,4-D, dicamba, and mecoprop to leave the plots in surface
water during a 2-inch rainfall at an intensity of 1 inch per
hour. The runoff was attributed to poor infiltration on a high
Michigan State University, Dr. Bruce Branham
- Nitrate leaching was negligible; less than 0.2% of the
applied nitrogen was recovered at a depth of 4 feet below the
surface (deepest system among all the studies).
- The nitrogen detected was at least 10 times below the
drinking water standard (0.43 ppm nitrate in spring and 0.77
ppm nitrate in fall).
- It is estimated that up to 34% of the nitrogen
- Only two (dicamba, triadimefon) of the eight pesticides
evaluated were detected in the percolate at four feet (levels
of 2 to 31 ppb).
- 2,4-D is potentially very mobile, but did not show up in
- Phosphorus leaching potential is very low except in some
sandy soils with low adsorption ability, where phosphorus
applications require closer management.
- The root zone and thatch had a high biological activity,
which enables turf to work like a filter when pesticide and
fertilizers are applied.
University of Massachusetts, Dr. Richard Cooper
- Volatile pesticide loss over the two-week observation
period ranged from less than 1% of the total material applied
for the herbicide MCPP, to 13% of the total applied for the
insecticides isazofos and trichlorfon.
- Volatile loss reached a maximum when surface temperature
and solar radiation were greatest. To minimize volatility, the
best time for application is late in the day.
- Total volatile loss for each compound was directly related
to vapor pressure. For all materials evaluated, most of the
volatile loss occurred during the first 5 days following
application. Volatile residues were undetectable or at
extremely low levels two weeks after application.
- Pesticide residues for all materials were rapidly bound to
the leaf surface, with less than 1% of all residues dislodging
(rubbed with cotton gauze) eight hours after application.
- Irrigating treated plots immediately after application
greatly reduced volatile and dislodgeable residues on the first
day following treatment
- Volatile losses were far below (up to 1000 times) levels
that should cause health concerns.
University of Nevada, Dr. Daniel Bowman
- When the turf was maintained under a high level of
management, nitrate leaching from both tall fescue and
bermudagrass turf was very low. A total of 1% or less of the
applied nitrogen was lost in the leachate.
- Irrigating the two turfgrasses with adequate amounts (no
drought stress) of moderately saline water did not increase the
concentration or amount of nitrate leached.
- Higher levels of salinity in the root zone, drought, or the
combination of these two stresses caused high concentrations
and amounts of nitrate to leach from both a tall fescue and
bermudagrass turf. This suggests that the nitrogen uptake
capacity of the turf root system is severely impaired by
drought, high salinity, or both. Under such conditions, it will
be necessary to modify management practices to reduce or
eliminate the stresses, or nitrate leaching could be a
University of California, Dr. Marylyn Yates
- Turf maintained under golf course fairway and putting green
conditions used most of the nitrogen applied - even with
- Under the conditions of this study (bi-weekly applications
of urea and sulfur-coated urea), little leaching of
nitrate-nitrogen (generally less than 1% of the amount applied)
was measured. No significant differences were found in the
percent leached as a result of irrigation amount or fertilizer
- Leaching of 2,4-D was very low in soils that contained some
clay, which adsorbs the pesticide; however, up to 6.5% leached
from the sandy putting green soil. Irrigation amount did not
significantly affect the amount of leaching.
- Less than 0.1% of the carbaryl leached, regardless of soil
type. The irrigation amount did not significantly affect the
amount of leaching.
- Little volatilization of 2,4-D was measured (Â£ 1%) from any
of the plots, although the difference in the amount volatilized
was significantly different between the two turfgrass species
used (bentgrass vs. bermudagrass) and the surface
characteristics (green vs. fairway).
- Little volatilization of carbaryl was measured (Â£ 0.05%)
from any of the plots.
- Based on uniformly low volatilization results, turf may
require different volatility regulations than agricultural
University of Florida, Dr. George Snyder
- A total of 98 to 99% of the insecticide applied stayed in
- Greater movement of the fenamiphos metabolite occurred than
expected, and different management practices may be warranted
with this product.
- Less than 1% of the applied pesticides were found on cotton
cloth immediately after spraying.
Cornell University, Dr. Martin Petrovic
- More leaching occurred in newly planted turf than in
mature, established turf.
- Nitrogen leaching did not exceed EPA drinking water
- During the first year, MCPP leached from a coarse sand with
poorly established turf (50 to 60% leached through the
profile). This treatment was a "worst case"
- During the second year, a 7-inch rain (hurricane
conditions) immediately after application caused substantial
leaching from all soils (_____ need % of total).
Penn State, Dr. Thomas Watschke
- Significant differences between water runoff from ryegrass
(more) versus creeping bentgrass (less) occurred because of the
presence of more stolons, more organic matter, and higher
density in bentgrass.
- Infiltration rate differences did not occur between the two
- Over time, the increase in thatch resulted in decreased
- The irrigation rate had to be doubled (6 inches/hr.) in
order to produce any runoff and indicates that turf is good at
- More than half of all the runoff water samples analyzed
contained no pesticide. The remaining contained pesticide
concentrations of less than 10 ppb of the pesticides.
- All reported nitrogen and phosphorous concentrations in
runoff were less than EPA drinking water standards.
- The process by which a chemical passes from one system into
another such as from the soil solution into a plant root or into
the matrix of a soil particle.
- A pesticide whose neutral (molecular) form becomes negatively
charged as pH is increased.
- Retention of a chemical onto the surface of a soil particle.
- The maximum amount of chemical that can be dissolved in water.
- A water-containing layer of rock, sand or gravel that will
yield useable supplies of water.
- A pesticide whose neutral (molecular) form becomes positively
charges as pH is lowered.
- A very strong, basic pesticide whose positive charge is
independent of pH.
- The chemical or biological transformation of the original
parent compound into one of more different compounds (degradates,
- The detachment of a pesticide from a soil particle.
- A state of dynamic balance, where forward and reverse reactions
or forces are equal and the system does not change with time.
- Water which saturates cracks, caverns, sand, gravel and other
porous subsurface rock formations. "Aquifers" are the
zones in which readily-extractable water saturates the pores of
- The time required for one-half of the original pesticide to be
degraded into another compound.
- A chemical degradation process resulting from the reaction of
an organic molecule (pesticide) with water under acidic or
- The stable fraction of the soil organic matter remaining after
the major portion of added plant and animal residues have
decomposed. Usually dark colored.
- See Soil Partition Coefficient.
- A study of time dependent processes. The kinetics of pesticide
adsorption indicates the rate at which pesticides are adsorbed by
- See Organic Carbon Partition Coefficient.
- The downward movement by water of dissolved or suspended
minerals, fertilizers, chemicals (pesticides) and other
substances through the soil.
MCL (Maximum Contaminant Level)
- An enforceable, regulatory standard for maximum permissible
concentrations as an annual average of contaminants in water.
MCL's are established under the Federal Safe Drinking Water
Act, which assures Americans of a safe and wholesome water
supply. The MCL standards of purity are applied to water
distribution systems after the water has been treated, regardless
of a surface or ground water source. They are health-based
numbers which by law must be set as close to the
"no-risk" level as feasible.
- A biological organism, microscopic in size, found in soils and
important in the degradation of most pesticides.
- The complete transformation or degradation of a pesticide into
carbon dioxide (CO2), water (H2O) and other inorganic products.
Nonpoint Sources of Contaminants
- Water contaminants coming from nonspecific sources; for
example, from agriculture and municipal runoff.
- A term used to describe a molecule (pesticide) whose electric
charge distribution is evenly distributed (no regions of positive
or negative charge). Nonpolar compounds are characterized as
being hydrophobic (water-hating) and not very soluble in water
but readily bound to organic matter.
Organic Carbon Partition Coefficient
- A universal constant used to describe the tendency of a
pesticide to sorb to the soil organic fraction component of a
soil. Often abbreviated as Koc.
- A chemical reaction involving the addition of an oxygen atom or
a net loss in electrons.
- The downward movement of water through soil.
- A numerical measure of acidity used to distinguish alkaline,
neutral and acidic solution. The scale is from 1 to 14; neutral
is pH 7.0, values below 7 are acidic, and above 7 are alkaline.
ppb (parts per billion)
- An abbreviation indicating the parts or mass of a pesticide in
a billion parts of water or soil.
ppm (parts per million)
- An abbreviation indicating the parts or mass of a pesticide in
a million parts of water or soil.
Point Sources of Contaminants
- Water contaminants from specific sources such as leaking
underground gasoline storage tank, back-siphoning of an
agrichemical into a well or spillage of a chemical near a water
- A term used to describe a molecule (such as a pesticide) whose
electrical charge distribution results in positively and
negatively charged regions on the molecule. Polar compounds ar
characterized as being hydrophilic (water-loving) and readily
soluble in water but not strongly bound to organic matter.
- A solid ionic compound (pesticide) made up from a cation other
than H+ and an anion other than OH1- or O2-.
Soil Organic Matter
- The organic fraction of soil which includes plant and animal
residues at various stages of decomposition, cells and tissues of
soil organisms, and substances synthesized by the soil
population. See also, Humus.
Soil Partition Coefficient
- A "soil specific" unit of measure used to describe
the sorption tendency of a pesticide to a soil. Often abbreviated
as Kd or Kp.
- A catch-all term referring to the processes of absorption,
adsorption or both.
- Most of the water lost by plants evaporates from leaf surfaces
by the processes of transpiration. Transpiration is essentially
the evaporation of water from cell surfaces and its loss through
the anatomical structures of the plant.
- A numerical unite of measure used to indicate the tendency of a
compound (liquid or solid) to volatilize or become a gas. A
commonly used unit of measurement for pesticide vapor pressure is
millimeters of mercury (abbreviated: mm Hg)
- The process by which chemicals go from a solid or liquid state
into a gaseous state.
- The top of an unpressurized aquifer, below which the pore
spaces generally are saturated with water. The aquifer is held in
place by an underlying layer of relatively impermeable rock. The
water table depth fluctuates with climatic conditions on the land
surface above, and the rate of discharge and recharge of the
Protecting ground and surface water from chemical pollutants is a
national initiative. The Environmental Protection Agency (EPA)
estimates that 1.2 billion pounds of pesticides are sold annually
in the United States. About 70 percent of the pesticides applied
are used for agricultural production of food and fiber. Only a
small fraction of this amount is used on golf courses. Yet,
increased public concern about chemicals has drawn attention to
golf because of the perception that the intense maintenance on
golf courses creates the potential for environmental