In the San Joaquin Valley, the organophosphorus insecticides diazinon,
chlorpyrifos, and methidathion are generally applied together
with a dormant oil on nut and stone fruit trees to control peach
twig borer, San Jose scale, European red mite, and brown mite
pests. The best time to achieve control is December through February,
when trees are dormant and better pesticide coverage is possible
(Zalom et al., 1995). The application period for dormant
sprays, however, also coincides with seasonal rainfall. As a result,
pesticide washoff may occur, allowing these compounds to enter
the San Joaquin River watershed and impact water quality (Ross
1992 and 1993).
Foe and Sheipline (1993) and Kuivila and Foe (1995) attributed
toxicity of Ceriodaphnia dubia to the presence of diazinon
and chlorpyrifos detected in the San Joaquin River watershed during
the 1991-1992 winter season. The Department of Pesticide Regulation
monitored the San Joaquin River watershed during the winters of
1991-1992 and 1992-1993 and reported the detection of diazinon,
chlorpyrifos, and methidathion in 72, 10, and 18% of the 108 water
samples collected, respectively (Ross 1992 and 1993). Of these
positive samples, 13, 2, and 1% exceeded the LC50 for
Ceriodaphnia dubia, indicating potential acute toxicity.
In addition, chronic toxicity to Ceriodaphnia dubia also
potentially exists, as mortality to these organisms was found
on 12 consecutive days in the San Joaquin River (Kuivila and Foe,
In prior field studies, the effectiveness of vegetation planted
in the orchard rows were examined as a method of reducing dormant
spray runoff during rain storm events (Ross, 1996, in preparation).
These methods will require further experimentation in commercial
orchards. In addition, investigation of other methods to reduce
insecticide runoff during storm events will be investigated here
to develop a variety of practices an orchard grower could adopt,
given his or her specific needs. Methods to be investigated in
small field plots include: 1) soil incorporation, 2) watering
in of applied pesticides, and 3) microbial augmentation. If any
of these methods significantly reduces insecticide runoff over
the control plots, these methods will be tested in commercial
orchards during winter months.
Baker and Laflen (1979) reported that incorporating three herbicides
into the soil and then exposing the plots to simulated rain, had
the potential to reduce runoff losses by a factor ranging from
4 to 13 when compared to plots compacted by tractor traffic and
plots with wheel track marks on the soil surface, respectively.
Greater than 80% of the herbicide losses were in solution. Incorporation
of the treated soil surface may reduce a pesticide's
availability for transport in runoff water due to the treated
soil being physically inverted below the soil surface, away from
water flow (Ciba-Geigy, 1992). Incorporation can also reduce rain
runoff by increasing the soil infiltration rate (Meek et al.,
1992) by loosening soil surface crusts, disrupting compact soil
layers, and by creating surface depressions which can temporarily
store water (Shainberg et al., 1992).
The addition of a light water application immediately following
pesticide treatment may also be a means to reduce pesticide runoff,
as pesticides may be moved down into the soil profile and therefore
have minimal contact with runoff water (Ciba-Geigy, 1992). Troiano
et al. (1990) reported that sprinkler application of water
following atrazine application resulted in the downward migration
of pesticide residue. Residue was confined to the upper subsurface
layers of soil and was, therefore, still available for degradation.
Microorganisms may also play a large role in pesticide degradation
and often times are the major means of pesticide dissipation in
the environment (Gauthier et al., 1988). Mullins et
al. (1989) reported that diazinon was degraded in a laboratory
disposal pit by a combination of biological and nonbiological
processes (hydrolysis), and that microorganisms were primarily
responsible for degradation of the hydrolysis product. Methidathion
was also reported to be degraded by a gram positive bacterial
organism that degraded about 20% of the applied pesticide within
15 days after pesticide application (Gauthier et al., 1988).
The objective of this protocol is to evaluate three management
practices which may reduce the movement of diazinon, chlorpyrifos,
and methidathion in runoff water from small field plots. These
management practices include: 1) soil incorporation, 2) application
of water to move the pesticides below the soil surface, and 3)
addition of microorganisms to the soil. Mass runoff from plots
treated with these methods will be compared using a completely
This study will be conducted by personnel from the Environmental
Hazards Assessment Program in the Environmental Monitoring and
Pest Management Branch of the California Department of Pesticide
Regulation. Study personnel include:
Project Leader and Field Coordinator: Clarice Ando
Statistician: Terri Barry
Laboratory Liaison: Cindy Garretson
Senior Scientist: Lisa Ross
Chemist: Paula Young
Agency and Public Contact: Peter Stoddard
All questions concerning this study should be directed to Peter
Stoddard at (916) 324-4100.
Study Plan and Sampling Methods
The study site will be located in a field that was recently planted
in young almond trees at the California State University, Fresno
campus. To reduce site differences within the field (since trees
were removed within the last six months) we plan to extensively
disk the study area to reduce the effects of previous cultural
practices. Each plot will then be laser leveled to a 1 percent
slope or less. This study site was selected primarily due to the
existence of an established irrigation system that is easily accessible.
The study design is a completely randomized design consisting
of four treatments randomized within 16 plots: 1) control, which
has no treatment, 2) soil incorporation following pesticide application,
3) water application using micro sprinklers following pesticide
application, and 4) addition of microbial soil amendment following
pesticide application (Table 1; Figure 1).
Table 1. Analysis of variance table for management practices
4-1 = 3
4(4-1) = 12
Each plot will encompass an area of 3 m x 5.5 m (10 ft by 18 ft)
and will be bordered by either a soil berm or other barrier to
define the plot area. A 8.5 m (28ft) buffer zone will be established
between plots to reduce cross contamination between adjacent plots.
At the down slope end of each plot, soil berms will be created
to divert runoff water through a stainless steel tube into a 19
l (5 gallon) container placed below the soil surface. This container
will be used to transfer water to a large trash receptacle that
will be used to quantify the amount of runoff water leaving each
plot during the simulated rain event.
Prior to pesticide application (approximately two to three days),
each plot will be pre-wetted with a known volume of water (through
artificial rainfall) in order to simulate damp soil conditions
as those observed in the field during the winter season. Also,
at this time any slope irregularities on the soil surface will
be removed if water ponding is observed on the soil surface.
To reproduce the damaging effects of winter rains on the soil
surface, overhead impact sprinklers will be elevated about 1.5
m above the ground surface to duplicate a similar kinetic energy
and droplet size to that of a heavy, natural rainfall. The simulated
rain event will occur 4 days after pesticide application and will
be applied to the length of each plot at an intensity similar
to a high rainfall occurrence observed during the winter months
when dormant sprays are applied. All 16 plots will receive the
same amount of artificial rainfall on the same day that will be
documented with the use of a flow meter and rain collection cans
placed within the plots. A pressure regulator and adjustment valve
will be installed to the irrigation system so that the water
pressure can be adjusted to achieve the same application rate
for all plots during the rain application period.
Sample collection for each plot will occur at a maximum of four
intervals during the runoff period. If an expected total maximum
of 80 l of rain runoff water is captured from the plots, then
sample collection will occur when 20, 40, 60, and 80 l are collected.
For each sampling period, three consecutive 1-liter water samples
will be collected as water drains from the plot prior to entering
the 19 l container. The first collected sample will be used for
whole chemical analysis, the second sample for filtered water
analysis, and the third sample will be held as a back-up sample.
Diazinon, chlorpyrifos, and methidathion will be applied together
in the same tank mix as was reported by Ross (1995) using a pickup-spray
rig to treat the plots at a rate of approximately 1.1 kg active
ingredient per hectare in 824 l of water (1 lb active ingredient
per acre in 87 gallons of water). Dormant spray oil will also
be applied with the pesticide mixture at a rate of 9.5 l per hectare
(one gallon per acre). Pesticide and oil will be applied to all
16 study plots on the same day. To determine the pesticide concentration
in the tank mix, two tank samples will be collected from a nozzle
on the spray day; one sample at the beginning of the spray period
and one sample at the end of the spray period.
Following pesticide application, pesticide treated soil will be
incorporated using a tractor and disk setup to disk the soil down
to a depth of 8 cm to 15 cm (3 to 6 inches). The water application
treatment using micro sprinklers will also occur following pesticide
application with the addition of one-half inch of water to the
appropriate plots. At sunset, the bacterial soil amendment will
be applied using a backpack sprayer at an appropriate application
Pesticide deposition will be monitored by placing three one-half
pint jars containing 50 g of soil onto each of the plots prior
to pesticide application. Each jar (open surface area of 45 cm2),
will be sunk into the ground so that the jar opening is flush
with the soil surface. Jars will be collected immediately following
application and frozen until chemical extraction. Concentrations
will be reported in ug pesticide/cm2
and ug pesticide/g of
To determine pesticide residue levels in soil, samples from each
plot will be collected prior to the pesticide application, prior
to the simulated rain event, and within 24 hr following the simulated
rain event after rain runoff ceases. Soil samples will be randomly
collected from each treatment using a stainless steel cylinder
with an internal diameter of 6 cm. Three soil cores will be removed
from each treatment using the cylinder that is pushed about 3
cm into the soil. The cores will be placed into a glass half-pint
jar and mixed to obtain a composite sample. Each composite sample
will weigh a minimum of 50 g; the minimum amount of soil necessary
for chemical analysis. Samples will be weighed in the field to
determine wet weight and will then be frozen until chemical extraction.
The concentration of each insecticide will be reported in total
ug per sample. Prior to chemical
analysis, an aliquot of soil will be removed to determine percent
moisture; wet and dry weight of this aliquot will be reported.
Prior to pesticide application, additional background soil will
be sampled as explained above to determine soil mechanical analysis
(Bouyoucos, 1962), pH, and organic carbon content (Rauschkolb,
1980). Two soil bulk density samples will be randomly collected
During one simulated rain event, rain runoff water will be collected
from each plot at specific intervals (as described above) and
analyzed for diazinon, chlorpyrifos, and methidathion. Whole water
samples will be analyzed for dissolved, suspended, and sediment-adsorbed
pesticide that is transported by water from the treated plot.
Filtered water samples will be analyzed for dissolved pesticide
and any suspended or sediment-adsorbed material that is not retained
by the filter in the filtration process. One back-up sample per
sampling period will be collected per plot. Also, on the day of the simulated rain event, two 1-liter samples of
the well water used to simulate artificial rainfall will also
be collected and analyzed for residues.
Whole water samples will be transported to the analyzing laboratory
and extracted within one week of sample delivery. Water samples
that require filtering prior to extraction will be filtered within
one week of sample collection using a Gelman Sciences type A/E
glass fiber filter (1 micron pore size) to remove total suspended
solids. Chemical extraction of the filtered water will occur within
one week of sample delivery to the analyzing laboratory.
Tank Mix Sample
Approx. three samples per treatment x 16 plots x 1 rain event (filtered water)............48
Two samples of well water used to simulate rain ........................................................2
Quality Control Samples
Total Number of Samples................................................................................................215
Mass balance of each pesticide deposited on site during application
will be determined from deposition jars collected immediately
after spraying. The mass of each pesticide in runoff water will
be expressed as total mass, and a percent of the total amount
of the theoretical applied or deposited (measured) on site. For
each pesticide, normalized mass values for water (per application
mass) will be used in analysis of variance to determine if treatment
differences exist. In addition, a mean separation test of water
results from the three treatments and the control will be conducted
for each pesticide.
Chemical Analytical Methods and Quality Control
Chemical analysis of soil and water samples for diazinon, chlorpyrifos,
and methidathion will be performed by Agriculture Priority and
Pollutants Laboratory in Fresno, California. Method development
and validation work will be conducted in accordance with Standard
Operating Procedure QAQC001.00. Continuing quality control will
also be conducted in accordance with Standard Operating Procedure
QAQC001.00. The reporting limits for water and soil are tentatively
set at 0.5 ppb and 7 ppb, respectively, for all 3 insecticides.
The California Department of Food and Agriculture Chemistry Services
in Sacramento, California, will analyze the tank sample for residues
of diazinon, chlorpyrifos, and methidathion.
Soil mechanical analysis and organic carbon content will
be determined using Bouyoucos (1962) and Rauschkolb (1980) methods,
respectively. Soil pH will be determined using a 1:10 water-soil
Field Setup: June 1996
Sample Collection: June 1996
Chemical Analysis: July 1996
Memorandum: August 1996
Report: September 1996
Figure 1. Diagram of completely randomized design consisting of three treatments and the control.
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herbicides as affected by wheel track and incorporation. J. Environ.
Bouyoucos, G.J. 1962. Hydrometer method improved for making particle
size analyses of soils. Agronomy J. 54:464-465.
Ciba-Geigy Corporation. 1992. Best management practices to reduce
runoff of pesticides into surface water: a review and analysis
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Public Affairs Department. Greensboro, NC.
Foe, C. and R. Sheipline. 1993. Pesticides in surface water from
applications on orchards and alfalfa during the winter and spring
of 1991-92. Central Valley Regional Water Quality Control Board.
Gauthier, M.J., J.B. Berge, A. Cuany, V. Breittmayer, D. Fournier.
1988. Microbial degradation of methidathion in natural environments
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study; Winter 1991-92. Memorandum to Kean Goh, Environmental Hazards
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study; Winter 1991-93. Memorandum to Kean Goh, Environmental Hazards
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