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How to Manage Pests

Pesticides: About Water-Related Risks of Active Ingredients—Compare Treatments

The Compare Treatments report shows the potential pesticide hazard due to loss of a pesticide by leaching or runoff from a high-risk soil (default), or a soil type you specify. The report lists hazards for all pesticides included in a UC IPM Pest Management Guideline (PMG) for a specific pest on a particular crop.

The page has three main features:

  • Risk comparison table
  • Change soil type, site conditions, and application conditions
  • See detail
Water-related risks -- compare treatments screen snapshot.

Risk comparison table

The risk comparison table provides potential pesticide hazard for each pesticide active ingredient included in the PMG, most often with a sample trade name to help you identify the pesticide.

The potential hazards shown in the table are based on the conditions listed at the top of the display:

  • Soil type and field conditions (soil type, field slope, macropores, water table)
  • Site condition (probability of rainfall or irrigation in the next 7 to 14 days)
  • Application conditions (pesticide amount, method, rate)

Initially, the display shows potential hazards based on a set of default conditions. For more accurate values, you must change the conditions to reflect your situation. Use the "Change" buttons and select the values that are mostly match your field.

The rating shown in the hazards comparison table takes into consideration the long-term toxicity of the pesticide. Potential hazard values are shown as bars. Bars vary in length based on low, intermediate, or high potential for off-site movement; shorter bars indicate less potential hazard. A letter abbreviation (V=very low, L=low, I=intermediate, H=high, X=extra high) appears next to the bar, and bars are also color-coded:

  • Blue (short) bars mean that potential hazard from off-site movement of the pesticide is low or very low, and no measures to mitigate runoff or leaching are likely to be needed.
  • Red (longer) bars mean that potential hazard is intermediate or high, and measures to mitigate runoff or leaching may be needed if the pesticide is used under the specified field conditions.

Ratings in the chart

Ratings come primarily from WIN-PST.

  • If the pesticide listed in the PMG is included in the USDA-NRCS WIN-PST database, WIN-PST's risk values are used.
  • If a pesticide is not included in WIN-PST, and the chemical poses no known risks to water quality, the table indicates "no known risk."
  • In all other cases where a chemical is not included in the WIN-PST database, risks are labeled "no information."

Leaching potential indicates the tendency of a pesticide to move in solution with water and to leach below the root zone. The rating in the chart is the potential pesticide hazard to fish or to humans due to leaching from soils that are highly susceptible to leaching, unless measures to mitigate leaching are used. If the soil is actually of a less-risky type, the potential hazard may be less. The hazard is based on long-term toxicity of the pesticide to fish and humans, not acute toxicity.

Ratings are VERY LOW, LOW, INTERMEDIATE, and HIGH. A VERY LOW or LOW rating indicates minimal movement and no need for mitigation. INTERMEDIATE and HIGH ratings indicate a greater potential for a pesticide to leach below the root zone, and measures to mitigate the impact may be needed. How is potential pesticide hazard to fish and humans, from leaching, determined?

Solution runoff potential indicates the tendency of a pesticide to move in surface runoff in the solution phase. The rating in the chart is the potential pesticide hazard to fish or to humans due to solution runoff from soils that are highly susceptible to runoff, unless measures to mitigate runoff are used. If the soil is actually of a less-risky type, the potential hazard may be less. The hazard is based on long-term toxicity of the pesticide to fish and humans, not acute toxicity.

Ratings are LOW, INTERMEDIATE, and HIGH. A HIGH rating indicates the greatest potential for pesticide loss in solution runoff, and use of pesticides with INTERMEDIATE and HIGH ratings may need mitigating measures. How is potential pesticide hazard to fish and humans, from solution runoff, determined?

Adsorbed runoff potential is the tendency of a pesticide to move in surface runoff attached to soil particles. The rating in the chart is the potential pesticide hazard to fish or to humans due to adsorbed runoff from soils that are highly susceptible to runoff, unless measures to mitigate runoff are used. If the soil is actually of a less-risky type, the potential hazard may be less. The hazard is based on long-term toxicity of the pesticide to fish and humans, not acute toxicity.

Ratings are LOW, INTERMEDIATE, and HIGH. A LOW rating indicates minimal potential for pesticide movement adsorbed to sediment, and no mitigation is required. INTERMEDIATE and HIGH ratings indicate a greater potential for a pesticide to move when attached to sediment, and measures to mitigate the impact may be needed. How is potential pesticide hazard to fish and humans, from adsorbed runoff, determined?

Change soil type and field conditions

The initial data in the table are computed for these standard soil type and field conditions:

  • DEFAULT soil highly susceptible to pesticide movement.
  • Field slope is less than 15%.
  • Field does not have macropores.
  • Field does not have a high water table.

Your soil type and field conditions may not be the same as these standard conditions. Because the soil type and field conditions can impact the risks to water quality, change these to accurately reflect

  • The soil type of your field.
  • Whether the field slope exceeds 15%.
  • Whether the field has macropores or cracks.
  • Whether the field has a high water table.

To use this feature,

  1. Click the "Change soil/field conditions" button (near the top left).
  2. Change the settings in the fields on the sequence of new screens that appear.

Note that when the program returns you to the main page, the revised soil type and field conditions will be displayed.

Change application conditions

The initial potential hazard ratings in the table are computed for these standard application conditions:

  • Application to more than 50% of the field (M) (sometimes called "broadcast").
  • Surface application (S).
  • Standard application rate of more than 1/4 pound active ingredient per acre (Q) (except for pyrethroids, which are always used at low rates).

Your rate and method may not be the same as these standard conditions. Because how you apply the pesticide can impact the risks to water quality, you may want to change the conditions to accurately reflect

  • The area you're treating.
  • How much pesticide will come in contact with the soil.
  • The actual application rate.

To use this feature,

  1. Select the chemical to change by clicking the button to the right of the chemical.
  2. Click the button next to the new condition(s) you want.
  3. Click "Change/Delete" button (on the left, below the last active ingredient in the table) after making your selections.

Note that one-letter abbreviations for the current application condition selections are shown in parentheses after each chemical. As you choose new conditions, the abbreviations will change.

What area is being treated?

  • Will you apply the pesticide to more than 50% of the field?
  • Or will you treat 50% or less of the field, by using strip applications, for instance?
  • Or will you treat 10% or less of the field, by using spot sprays, for instance?

How much pesticide will come in contact with the soil?

  • Surface applied means that you will apply the pesticide to bare ground or an incomplete canopy.
  • Foliar applied means that you will apply the pesticide when the crop or weeds are at nearly full canopy. Dormant sprays are not "foliar applied."
  • Soil incorporated means that you will incorporate the pesticide into the soil.

What is the application rate?

  • Rates above 1/4 pound of active ingredient per acre are considered the "standard" rate by the program.
  • Rates from 1/10 to 1/4 pound active ingredient per acre are considered to be low by WIN-PST.
  • Rates less than 1/10 pound of active ingredient per acre are considered to be ultra low by WIN-PST.

Note: If you don't know the percent active ingredient for a product, to calculate pounds of active ingredient per acre, you can look up the product in an online database.

Change site condition

The initial data in the table are computed for this standard site condition:

  • Low probability of rainfall/irrigation expected within 7-14 days of pesticide application.

Your situation may not be the same as this standard condition. Because rainfall and/or irrigation can impact the risks to water quality, you may want to change this condition to reflect

  • Rainfall has occurred (or will likely occur) within 7-14 days of pesticide application.
  • Irrigation was done, or is planned, within 7-14 days of pesticide application.

To use this feature,

  1. Click Change*.
  2. Click the low or high probability option you want.
  3. Click "Change site condition" button after making your selection

Note that when the program updates the page, the change you made will be displayed.

See detail

If you want more data about these chemicals and their potential hazards, you may request it in tabular form.

Under "See detail," you may choose

  • Table (to print)
  • Data file

These selections will give additional data values from WIN-PST, and the tabular report mimics those in WIN-PST. The data file contains the same information as the one for print, except that commas separate the values for importing into a spreadsheet.


Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2014 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

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