Department of Pesticide Regulation

Environmental Monitoring and Pest Management

1020 N Street, Room 161

Sacramento, CA 95814-5624

May 24, 1996

Investigation of Possible Management Practices to Reduce Dormant Spray Runoff

from Soil Plots


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, 1995).

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 randomized design.


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

Source of Variation

Degrees of Freedom


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.

Pesticide Application

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.

Treatment Application

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 rate.

Pesticide Deposition

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 soil.

Soil Sampling

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 per plot.

Water Sampling

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.

Sample Number

Tank Mix Sample

Deposition Samples

Soil Samples

Water Samples

Quality Control Samples

Total Number of Samples................................................................................................215

Data Analysis

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 ratio.


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.

Figure 1. Diagram of completely randomized design consisting of three treatments and the control.


Baker, J.L. and J.M. Laflen. 1979. Runoff losses of surface-applied herbicides as affected by wheel track and incorporation. J. Environ. Qual. 8:602-607.

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 of supporting research. Technical Report:9-92. Environmental and 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 and metabolization of this pesticide by Bacillus coagulans. Pest. Biochem. Phys. 31:61-66.

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Ross, L.J. 1996. Report in preparation. Environmental Hazards Assessment Program, California Department of Pesticide Regulation.

Ross, L.J. 1995. Reducing dormant spray runoff from orchards. Protocol. Environmental Hazards Assessment Program, California Department of Pesticide Regulation, November 15, 1995.

Ross, L.J. 1992. Preliminary results of the San Joaquin River study; Winter 1991-92. Memorandum to Kean Goh, Environmental Hazards Assessment Program, California Department of Pesticide Regulation, May 22, 1992.

Ross, L.J. 1993. Preliminary results of the San Joaquin River study; Winter 1991-93. Memorandum to Kean Goh, Environmental Hazards Assessment Program, California Department of Pesticide Regulation, September 23, 1993.

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Standard Operating Procedure Number:QAQC001.00. Chemistry Laboratory Quality Control. California Department of Pesticide Regulation, Environmental Hazards Assessment Program, Sacramento, California.

Troiano, J., C. Garret son, C. Krauter, and J. Brownell. 1990. Atrazine leaching and its relation to percolation of water as influenced by three rates and four methods of irrigation water application. California Department of Pesticide Regulation. EH 90-7, Sacramento, California.

Zalom, F.G., R.A. Van Steenwyk, W.J. Bentley, R. Coviello, R.E. Rice, W.W. Barnett, C. Pickel, M.M. Barnes, B.L. Teviotdale, W.D. Gubler, and M.V. McKenry. 1995. Almond pest management guidelines. University of California, Division of Agriculture and Natural Resources, UCPMG Publication 1.