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How to Manage Pests

Pesticides: About the WIN-PST Database

The USDA NRCS West National Technology Support Center, Water Quality and Quantity National Technology Development Team, developed and supports the Windows Pesticide Screening Tool (WIN-PST). WIN-PST is a tool for screening environmental risk of pesticides that NRCS field office conservationists, extension agents, crop consultants, pesticide dealers, and producers can use to evaluate the potential for pesticides to move with water and eroded soil/organic matter and to affect nontargeted organisms.

WIN-PST considers the impact of soil characteristics, irrigation/rainfall probability, and pesticide application area, method, and rate on the potential for pesticides to move off-site.

WIN-PST users can specify pesticides by product name or active ingredient. Long-term human and fish toxicity data and ratings are also included in WIN-PST. These toxicity ratings can be combined with the off-site movement potential ratings to provide an overall rating of the potential risks from pesticide movement below the root zone and past the edge of the field.

WIN-PST and the Pesticide Properties Database

The WIN-PST/NAPRA Pesticide Properties Database (PPD) forms the basis of WIN-PST. The database is composed of data from a variety of sources and contains EPA registration data (EPA REG DB), representative value pesticide property data (source indicated by the G/E field in the data tables), and toxicity data for humans and fish (from Stephen Plotkin's toxicity database).

The WIN-PST/NAPRA PPD is maintained by Steve Plotkin and Eric Hesketh.

WIN-PST and the Soil/Pesticide Interaction Procedure version 2 (SPISP II)

WIN-PST is based on algorithms contained in

Goss, D., and R. D. Wauchope. 1990. The SCS/ARS/CES Pesticide Properties Database: II, Using it with soils data in a screening procedure. In Proceedings of the Third National Research Conference On Pesticides, November 8-9, 1990, Richmond, Virginia. D. L. Weigmann, ed.

Who maintains WIN-PST?

WIN-PST is supported by the USDA NRCS West National Technology Support Center. The Water Quality and Quantity Technology Development Team contacts are the following:

Joseph K. Bagdon  Pest Management Specialist and NAPRA/WIN-PST Team Leader
  joseph.bagdon@ma.usda.gov  (413) 253-4376

Eric S. Hesketh  Soil Scientist/Pest Management Specialist
  eric.hesketh@ma.usda.gov  (413) 253-4374

Stephen Plotkin  Water Quality Specialist
  stephen.plotkin@ma.usda.gov  (413) 253-4377

WIN-PST data definitions

Data provided in UC IPM's WaterTox are pulled from the PPD and adjusted using WIN-PST algorithms. Below are definitions and descriptions of the PPD and WIN-PST data fields shown in the WaterTox detailed table or closely related to them. The descriptions are from the file "glossary.txt" distributed as part of WIN-PST, with minor editorial revisions.

The WaterTox detailed report is equivalent to the WIN-PST SPISP II Pesticide Active Ingredient Rating Report, with the addition of the PC_Code and a sample trade name.

Pesticide names

Active ingredient common name
PC_Code

Chemical properties

pH
Solubility in water
Half-life
Koc

SPISP II P-Ratings

PLP  PSRP  PARP

Toxicity

Human
Fish

Soil properties

STSSAID
MUSYM
 
 

SPISP II I-Ratings

ILP  ISRP  IARP

Exposure Adjusted Toxicity Category

Human
Fish

Site conditions

Probability of rainfall/irrigation
 
 
 

SPISP II S-Ratings

SLP  SSRP  SARP

Pesticide names: Active ingredients, products, and their codes

Active Ingredient Common Name (AI_NAME)

Common name associated with an active ingredient. Common name followed by "(ANSI)" indicates acceptance of name by American National Standards Institute.

PC_CODE

EPA active ingredient registration number (also known as Shaughnessy Code).

EPA Product Names

A product is a commercially available formulation of one or more active ingredients mixed with adjuvants and inert ingredients. When a pesticide product is sold to the public, it must have an EPA registration number that appears on the product label. An EPA registration number may be associated with many different product names depending on the wholesaler or retailer. The EPA product database used in WIN-PST includes the original registration name for a given product. Since EPA allows manufacturers or dealers to change the name of the product associated with a particular formulation and add new names, some product names for currently registered products will not appear in WIN-PST. Ratings for these products are still available through the EPA registration number. All name differences can be ignored if the EPA registration numbers are identical.

EPA REG DB

EPA Registration Database. Updated monthly. This database can be accessed online.

Chemical properties

pH

In general, pH is a numerical measure of acidity or hydrogen ion activity. pH < 7.0 is acidic. pH 7.0 is neutral. pH > 7.0 is alkaline (basic).

In the WIN-PST PPD, pH represents the value at which the solubility in water, field half-life, and Koc (SOL, HL, Koc) are valid.

  • When determining P-Ratings, appropriate properties are selected based on field soil pH.
  • If the pH field is blank, assume that the SOL, HL, and Koc for this active ingredient are pH-insensitive and therefore that these properties are valid at any soil pH.
  • A pH reading of 5 is ten times more acidic than a reading of 6, and 6 is ten times more acidic than a reading of 7. Most adult fish die in water at a pH of 5 or below.
Solubility in Water (SOL)

Solubility is the measure of an active ingredient's ability to dissolve in water at room temperature. It is expressed in mg/L (ppm) and is used to compute the pesticide ratings in SPISP II.

Solubility is a fundamental physical property of a chemical and affects the ease of wash off and leaching through soil. In general, the higher the solubility value, the greater the likelihood for movement.

Half-life (HL)

Soil half-life of an active ingredient under field conditions, in days. Sometimes referred to as field dissipation half-life. Used to compute the pesticide ratings in SPISP II.

Half-life is the time required for a pesticide to degrade to one-half of its previous concentration. Each successive elapsed half-life will decrease the pesticide concentration by half. For example, a period of two half-lives will reduce a pesticide concentration to one-fourth of the initial amount. Half-life can vary by a factor of three or more from reported values depending on soil moisture, soil pH, temperature, oxygen status, soil microbial population, and other factors. Additionally, resistance to degradation can change as the initial concentration of a chemical decreases. It may take longer to decrease the last one-fourth of a chemical to one-eighth than it took to decrease the initial concentration to one-half. In general, the longer the half-life, the greater the potential for pesticide movement.

Koc

Soil organic carbon sorption coefficient of an active ingredient in mL/g. Used to compute the pesticide ratings in SPISP II.

Pesticides vary in how tightly they are adsorbed to soil particles. Koc measures the affinity for pesticides to sorb to organic carbon. The higher the Koc value, the stronger the tendency to attach to and move with soil. Soil pH can affect the Koc of ionic and partially ionic pesticides. A pesticide with an anion as the active species would have a Koc set low to account for that pesticide's inability to sorb to soil particles. A cationic active species would tend to bind strongly with soil and therefore have a relatively high Koc.

Pesticide Koc values greater than 1,000 indicate strong adsorption to soil. Pesticides with lower Koc values (less than 500) tend to move more with water than adsorbed to sediment.

Soil properties

STSSAID (State Soil Survey Area ID)

STSSAID is a concatenation of the federal (FIPS) alpha code for a state and the soil survey area symbol.

MUSYM (Mapunit Symbol)

MUSYM is used to identify the soil mapunit on the soil map.

Soil-related conditions that affect ratings

Slope of the field. If the field slope is greater than 15%, then pesticide is more likely to move off-site. The rating for soil sensitivity to pesticide loss (SARP) is increased by one class.

Macropores. Surface-connected holes or cracks that extend deeper than 24 inches into the soil. Where macropores are present, pesticides are more likely to move below the target zone.

Water table. A high water table occurs when the apparent water table comes withing 24 inches of the surface during the growing season. Presence of a high water table increases soil leaching potential to high, regardless of other conditions.

Site conditions

Probability of rainfall/irrigation

The probability of rainfall or irrigation within 7 to 14 days of a pesticide application (high or low) affects the ILP, ISRP, IARP.

Toxicity

Human Toxicity

Long-term human toxicity of an active ingredient in parts per billion (ppb). Toxicities are based on availability in the following priority order (see below for definitions): MCL, HA, HA*, and CHCL*.

  • MCL is used whenever available by the EPA Office of Water.
  • HA and HA* are used for Cancer
  • CHCL* is used for Cancer Groups A, B1, and B2 when MCL is unavailable.

Toxicity Information Type:
MCL—EPA's Maximum Contaminant Level. Maximum permissible long-term pesticide concentratin allowed in a public water source. MCL is used in WIN-PST for any pesticide for which EPA has an assigned value. In the absence of an MCL, an HA, HA*, or CHCL* is used in WIN-PST.

HA—Health Advisory, determined by EPA's Office of Water. The concentration of a chemical in drinking water that is not expected to cause any adverse noncarcinogenic effects over a lifetime exposure with a margin of safety. HA is compared to the PLP or PSRP for humans.

HA*—Health Advisory calculated using the EPA method for calculating HA based on Reference Dose (RFD). RFD values are from the EPA Office of Pesticide Programs (OPP), EPA, or World Health Organization (WHO).

  • The EPA OPP RFD is updated regularly and when available is used to determine HA*.
  • If the RFD from EPA OPP is not available, then the EPA RFD is used. EPA RFD is an agency-wide value that is not updated as regularly or as often as the OPP RFD.
  • If neither of these values is available, then the WHO RFD is used.

In accordance with OW policy, Health Advisories are not calculated for chemicals that are known or probably human carcinogens (EPA Cancer Class A and B).

CHCL*—Chronic Human Carcinogen Level, calculated. The concentration at which there is a 1 in 100,000 probability of contracting cancer; calculated by using the EPA algorithm based on QSTAR from animal studies. A CHCL provides a concentration comparable to an MCL.

Algorithm:

CHCL* = (70 Kg * 10^-5) / (2 L/day * QSTAR)

  • 10^-5 represents a 1/100,000 chance of contracting cancer.
  • 70 Kg represents the average weight of an adult.
  • 2 L/day represents average consumption of water each day by an adult.

Reference: "Drinking Water Health Advisory: Pesticides"  United States Environmental Protection Agency  Office of Drinking Water Health Advisories  Lewis Publishers  Pages viii – xiii, 1994

Fish Toxicity

Fish toxicity for an active ingredient in parts per billion (ppb).

MATC*—Maximum AcceptableToxicant Concentration in ppb. MATC* is the long-term toxicity value for fish. The MATC* for an active ingredient can be determined empirically by performing long-term or early life-stage toxicity tests. These test results produce the No Observable Effect Concentration (NOEC) and Lowest Observable Toxicant Concentration (LOEC).

  • Empirically, the geometric mean of the NOEC and LOEC is the MATC*. When both the NOEC and the LOEC were available, MATC* was determined in this manner.
  • When either the NOEC or the LOEC (or both) was unavailable, MATC* was determined from a regression equation using the 96-hour LC50 in the method described by Barnthouse et al., (1990).
  • In rare instances, empirically derived MATC* values were found to be larger than the 96-hour LC50 for that chemical. This may occur when the toxicity tests for the 96-hour LC50 and the NOEC/LOEC are performed:
    • Under different water quality conditions (hardness, alkalinity, pH, temperature, etc.).
    • With different species of fish.
    • With different products which use this active ingredient (AI). Occasionally, pesticide toxicity can be attributed to the inert ingredients in the formulation of a product which contains this AI, rather than the AI itself.
  • When the empirically derived (NOEC/LOEC) MATC* is larger than the 96-hour LC50, an MATC* computed using the Barnthouse method is used instead.

The MATC* for an active ingredient is used in several ways in WIN-PST:

  • To compute the WIN-PST Exposure Adjusted Toxicity Rating to fish for pesticide in solution.
  • To compute the WIN-PST Exposure Adjusted Toxicity Rating to fish for pesticide adsorbed to sediment. This is called the Sediment Toxicity Value (STV). STV = KOC * MATC*.

STV—Sediment Toxicity Value.STV = Koc * MATC*. Compared to the PARP when the species of concern are fish. STV provides toxicity of pesticide sorbed to detached soil leaving the field. Koc is used in STV determination to estimate pesticide concentration in sediment pore water. Fish MATC is used in lieu of toxicity data to sediment-dwelling animals for which test data are rare. STV thresholds ratings are the same as those used for MATC evaluation. The method for sediment short-term toxicity of nonionic pesticides (Di Torro et al., 1991), was modified to determine long-term toxicity. STV is also used to evaluate ionic pesticides which account for 25% of pesticides. This is achieved by use of an adjusted Koc in the NAPRA PPD, which accounts for pesticide ionic properties.

Reference: Di Torro, D. M., C. S. Zarba, D. J. Hansen, W. J. Berry, R. C. Swartz, C. E. Cowan, S. P. Pavlou, H. E. Allen, N. A. Thomas, P. R. Paquin. 1991. "Technical Basis for Establishing Sediment Quality Criteria for Nonionic Organic Chemicals Using Equilibrium Partitioning." Environmental Toxicology and Chemistry 10: 1541-1583.

Exposure Adjusted Toxicity Ratings (Called Potential Hazard in UC IPM's WaterTox)

Water, for humans

Determines the soluble pesticide toxicity level for humans. The long-term human toxicity based on MCL, HA, HA* or CHCL*. Used to determine relative hazard.

These ratings combined with the I-Ratings in the Interaction Exposure Adjusted Toxicity Matrix evaluate the relative risk to the environment of a pesticide active ingredient. UC IPM's program always uses a high (H) S-Rating in determining the exposure adjusted toxicity ratings for its default display. When a user specifies a soil type, the display is based on ratings for that soil.

Ratings reported in WIN-PST:
EXTRA HIGH 1 ppb > X
HIGH 10 ppb > X >= 1 ppb
INTERMEDIATE 50 ppb > X >= 10 ppb
LOW 100 ppb > X >= 50 ppb
VERY LOW X >= 100 ppb

Water, based on MATC*, for fish

Soluble pesticide toxicity level for fish. Used to determine relative hazard. These ratings combined with the I-Ratings in the Interaction Exposure Adjusted Toxicity Matrix evaluate the relative risk to the environment of a pesticide active ingredient. UC IPM's program always uses a high (H) S-Rating in determining the exposure adjusted toxicity ratings for its default display. When a user specifies a soil type, the display is based on ratings for that soil.

Ratings reported in WIN-PST:
EXTRA HIGH 1 ppb > X
HIGH 10 ppb > X >= 1 ppb
INTERMEDIATE 100 ppb > X >= 10 ppb
LOW 500 ppb > X >= 100 ppb
VERY LOW X >= 500 ppb

Sediment, based on STV, for fish

Pesticide adsorbed to sediment toxicity level for fish. Used to determine relative hazard. These ratings combined with the I-Ratings in the Interaction Exposure Adjusted Toxicity Matrix evaluate the relative risk to the environment of a pesticide active ingredient. UC IPM's program always uses a high (H) S-Rating in determining the exposure adjusted toxicity ratings for its default display. When a user specifies a soil type, the display is based on ratings for that soil.

Ratings reported in WIN-PST:
EXTRA HIGH 10 ppb > X
HIGH 100 ppb > X >= 10 ppb
INTERMEDIATE 1,500 ppb > X >= 100 ppb
LOW 20,000 ppb > X >= 1,500 ppb
VERY LOW X >= 20,000 ppb

SPISP II P-ratings (Pesticide ratings)

The ratings are derived from the Soil Pesticide Interaction Procedure version 2 (SPISP II) (Goss and Wauchope, 1990), adjusted for management (application area, rate, or method).

Pesticide Adsorbed Runoff Potential (PARP)

PARP indicates the tendency of a pesticide to move in surface runoff attached to soil particles. A low rating indicates minimal potential for pesticide movement adsorbed to sediment, and no mitigation is required.

PARP is calculated according to a WIN-PST algorithm, then the resulting rating is adjusted for management.

Management:
Foliar: -1 rating class
Banded (10-50% of the field): -1
Spot Treatment (<10% of the field): -2
Soil Incorporated: -1
Low rate: -1
Ultra-low rate: -2

Pesticide Leaching Potential (PLP)

PLP indicates the tendency of a pesticide to move in solution with water and leach below the root zone. A low rating indicates minimal movement and no need for mitigation.

PLP is calculated according to a WIN-PST algorithm, then the resulting rating is adjusted for management.

Management:
Foliar: -1 rating class
Banded (10-50% of the field): -1
Spot Treatment (<10% of the field): -2
Soil Incorporated: +1
Low rate: -1
Ultra-low rate: -2

Pesticide Solution Runoff Potential (PSRP)

PSRP indicates the tendency of a pesticide to move in surface runoff in the solution phase. A high rating indicates the greatest potential for pesticide loss in solution runoff.

PSRP is calculated according to a WIN-PST algorithm, then the resulting rating is adjusted for management.

Management:
Foliar: -1 rating class
Banded (10-50% of the field): -1
Spot Treatment (<10% of the field): -2
Soil Incorporated: -1
Low rate: -1
Ultra-low rate: -2

Rating adjustments

Ratings on the reports are not necessarily SPISP II ratings. These ratings may have been adjusted for management and site characteristics. WIN-PST allows the user to select one of the management techniques listed below from each group. The adjusted ratings are then used to compute the final ratings shown in reports.

Site conditions and management techniques, and their abbreviations

  • (none)—Broadcast application (Unadjusted); applied to more than 1/2 the field
  • b—Banded application; applied on 1/10 to 1/2 of the field
  • p—Spot Treatment; applied to 1/10 the field or less
  • (none)—Surface applied (Unadjusted); applied to the soil surface
  • i—Soil incorporated; with light tillage or irrigation
  • f—Foliar application; directed spray at nearly full crop/weed canopy
  • (none)—Standard rate of application (Unadjusted); greater than 1/4 lb/acre
  • l—Low rate of application; 1/10 to 1/4 lb/acre
  • ul—Ultra Low rate of application; 1/10 lb/acre or less
Management adjustments to risk ratings

Pesticide application area

  • Broadcast. The default pesticide application area. Broadcast is application over more than 50% of the field. Broadcast, banded, and spot treatment applications of a pesticide are mutually exclusive.
  • Banded application. Pesticide application over 50% or less of the field. This typically involves pesticide application over the rows. Banding pesticide application can reduce the P-Ratings by one class since it reduces pesticide application to the field by 50%. Banded: -1 PLP, -1 PSRP, -1 PARP
  • Spot Treatment. Pesticide application over 10% or less of the field. Spot treatment application can reduce the P-Ratings by two classes since it reduces pesticide application to the field by 90%. Spot Treatment: -2 PLP, -2 PSRP, -2 PARP

Application method

  • Foliar application. Foliar pesticide application utilizing a directed spray when the crop and/or weeds are at nearly full canopy. This increases interception of pesticide by the plant and decreases contact with the soil. Dormant applications to trees are not considered foliar applications. Foliar application allows reduction of the P-Ratings by one class.
  • Soil incorporated. Pesticide incorporated into soil. Incorporation decreases pesticide runoff but increases percolation. Soil Incorporated: Soil Incorporated: +1 PLP, -1 PSRP, -1 PARP.
  • Surface applied. The default pesticide application method. Surface applied, soil incorporated, and foliar pesticide application are mutually exclusive.

Application rate

  • Standard rate. The default pesticide application rate. A label rate greater than 1/4 lb active ingredient per acre (280 grams per hactare).
  • Low rate. A pesticide application rate of 1/10 to 1/4 lb active ingredient per acre. (112 to 280 g/ha.) A low application rate can reduce the P-Ratings by one class.
  • Ultra-low rate. A pesticide application rate of 1/10 lb or less active ingredient per acre. (112 g/ha.) An ultra low rate of application allows reduction of the P-Ratings by two classes.

Management actions, when applied to the SPISP II pesticide leaching potential, pesticide solution runoff potential, and pesticide adsorbed runoff potential, adjust ratings according to the following rules:

Action PLP PSRP PARP
b -1 -1 -1
p -2 -2 -2
i +1 -1 -1
f -1 -1 -1
b+i   -1 -1
b+f -1 -1 -1
p+i -1 -2 -2
p+f -2 -2 -2
 
l -1 -1 -1
ul -2 -2 -2
 
b+l -1 -1 -1
b+ul -2 -2 -2
p+l -2 -2 -2
p+ul -2 -2 -2
i+l   -1 -1
i+ul -1 -2 -2
f+l -1 -1 -1
f+ul -2 -2 -2
b+i+l -1 -1 -1
b+i+ul -2 -2 -2
b+f+l -1 -1 -1
b+f+ul -2 -2 -2
p+i+l -2 -2 -2
p+i+ul -2 -2 -2
p+f+l -2 -2 -2
p+f+ul -2 -2 -2

Legend:
+1: Increase rating by 1 class. (Increased Loss Potential)

(none): No effect.

-1: Decrease rating by 1 class. (Decreased Loss Potential)

-2: Decrease rating by 2 classes. (Decreased Loss Potential)

WIN-PST evaluates the cumulative effect of these conditions on the ratings as follows:

1. All of the conditions for a given loss category are assessed collectively. Each condition contributes an incremental (+ —increased sensitivity / risk) or decremental (- —decreased sensitivity / risk) effect on the ratings. The sum of all of these conditions is used in step 2, below.

2a. If the sum of all of the conditions is negative, the rating is reduced by one class. If the sum of all the conditions is positive, the rating is increased by one class. Thus, two or more incremental or decremental conditions only change the original SPISP II rating by one class, except as shown in 2b, below.

2b. Exceptions:

  • An ultra low or spot treatment pesticide application rate can reduce the P-Ratings by two classes.
  • The presence of a high water table during the growing season makes the SLP HIGH.

Reference "The SCS/ARS/CES Pesticide Properties Database: II, Using it with soils data in a screening procedure." Don Goss and R. Don Wauchope. In Pesticides in the Next Decade: The Challenges Ahead, Proceedings of the Third National Research Conference On Pesticides, November 8-9, 1990. Diana L. Weigmann, Editor, Virginia Water Resources Research Center, Virginia Polytechnic Institute & State University. Pg. 471-487.

SPISP II S-ratings (Soil vulnerability ratings)

Soil Leaching Potential (SLP)

SLP is the sensitivity of a specific soil to pesticide leaching below the rootzone. SLP characterizes those soil properties that would increase or decrease the tendency of a pesticide to move in solution with water and leach below the root zone. A high rating indicates the greatest potential for leaching.

SLP is calculated according to a WIN-PST algorithm, then the resulting rating is adjusted for site conditions.

Macropores: +1 rating class
High water table: High

Soil Solution Runoff Potential (SSRP)

SSRP is the sensitivity of a given soil to pesticide loss dissolved in surface runoff that leaves the edge of the field. A high rating indicates the greatest potential for solution surface loss.

SSRP is calculated according to a WIN-PST algorithm, but no site condition adjustments apply.

Soil Adsorbed Runoff Potential (SARP)

SARP represents the sensitivity of a soil to loss of pesticide adsorbed to sediment and organic matter that leaves the edge of the field. SARP characterizes those soil properties that would increase or decrease the tendency of a pesticide to move in surface runoff attached to soil particles. A high rating indicates the greatest potential for sediment/pesticide transport.

SARP is calculated according to a WIN-PST algorithm, then the resulting rating is adjusted for site conditions.

Field slope > 15%: +1 rating class

SPISP II I-ratings (Soil/pesticide loss interaction ratings)

Soil/pesticide interaction ratings (ILP, ISRP, and IARP) result from the PLP, PSRP and PARP pesticide ratings are combined with SLP, SSRP and SARP soil ratings in a Soil/Pesticide Interaction Matrix that results in ILP, ISRP and IARP Soil/Pesticide Interaction ratings.

The interaction ratings provide a relative potential for pesticide loss for each soil/pesticide combination.

Soil/Pesticide Interaction Leaching Potential (ILP)

ILP ratings indicate the potential for pesticides to leach below the root zone. ILP is computed from the PLP and SLP according to the matrix below, then adjusted for rainfall and/or irrigation.

               PLP
SLP          | High          Intermediate  Low            Very Low
-------------|----------------------------------------------------
High         | High          High          Intermediate   Low
Intermediate | High          Intermediate  Low            Very Low
Low          | Intermediate  Low           Low            Very Low
Very Low     | Low           Low           Very Low       Very Low

Adjustments to matrix-derived rating:
Low  rainfall, no irrigation: -1
			
Soil/Pesticide Interaction Solution Runoff Potential (ISRP)

ISRP ratings indicate the potential for pesticides to move beyond the edge of the field when they are dissolved in solution runoff.

ISRP is computed from the PSRP and SSRP according to the matrix below, then adjusted for rainfall and/or irrigation.

               PSRP
SSRP         | High          Intermediate    Low
-------------|-------------------------------------------
High         | High          High            Intermediate
Intermediate | High          Intermediate    Low
Low          | Intermediate  Low             Low

Adjustments to matrix-derived rating:
Low  rainfall, no irrigation: -1
			
Soil/Pesticide Interaction Adsorbed Runoff Potential (IARP)

IARP ratings indicate the potential for pesticides to move beyond the edge of the field adsorbed to sediment and organic matter that is suspended in runoff water.

IARP is computed from the PARP and SARP according to the matrix below, then adjusted for rainfall and/or irrigation.

              PARP
SARP         |High         Intermediate   Low
-------------|----------------------------------------
High         |High         High           Intermediate
Intermediate |High         Intermediate   Low
Low          |Intermediate Low            Low

Adjustments to matrix-derived rating:
Low  rainfall, no irrigation: -1
			

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