Oklahoma State University

PEET Herbicide Documentation Introduction

Introduction  PEET’s Use, Database Development,
Cautions/Disclaimers, Inputs, and Outputs


PEET Herbicide Documentation


Shea W. Murdock, David L. Nofziger, Don S. Murray, and Case Medlin



Herbicide application decisions in cotton and peanuts are difficult and complex for most producers, especially with the advent of several new, highly efficacious herbicides and the commercialization of herbicide-resistant cotton cultivars.  These new weed management tools have made weed control easier, but have made the decision process more complex.  Producers must now decide if, when, and what herbicides should be applied based on economic thresholds.  The economic threshold is complicated, difficult, and time consuming to calculate, should be calculated for each possible herbicide option, and should include factors such as expected crop price, expected crop yield, weed species and population, weed-crop competition, herbicide price, and herbicide efficiency.  Due to the complexity of these calculations, most producers rely on others to make their herbicide decisions.  However, a computer “Decision Support System” (DSS) can aid producers in making these difficult and complex weed control decisions.

With inputs from the user, PEET (Predicting Environmental & Economic Tradeoffs…) compares the economic benefits and potential groundwater hazards of various herbicide treatments.  The complex calculations are performed in real-time, giving the producer many herbicide options to choose from in a matter of seconds.  Like all computer models, PEET is not intended to replace human knowledge in decision-making, but only to “aid” in the process. 


Database development:

For models and equations used in PEET, see the PEET Documentation section in the “Help” menu.  The PEET databases were developed from the knowledge of Oklahoma State University weed and soil scientists.  The weeds in the database are common to most Oklahoma cotton and peanut fields.  Herbicide rates and application information are based on manufacturers’ labels.  Herbicide efficacies (i.e. percent control of a weed by a herbicide treatment) were derived from research trials performed in Oklahoma and surrounding states when possible, and from herbicide labels in conjunction with conservative estimates when research was not available.  Treatment efficacies depend upon the weed species, size, soil moisture, and environmental conditions.

Competitive indices, CI’s, are scores of the competitiveness of a weed species with a crop.  CI’s are generally based on and validated with years of weed competition research, but estimates are used when needed (Figure 1.).   


Figure 1.  The chart above depicts devils’-claw (·) with a CI of 10, the highest CI rating, with the yield prediction loss of the model ().  The actual cotton yield loss resulting from devils’-claw competition, attained from weed versus crop competition research performed at OSU, is plotted against the total competitive load (TCL), which was obtained by multiplying the weed density by the CI.  The model’s prediction is also included to compare the accuracy of the model in predicting the yield loss for devils’-claw at the corresponding TCL levels.


Validation of the data: Field experiments were conducted during the last several years to assess the accuracy or dependability of PEET compared to human recommendations.  Each year small adjustments were made to the program to increase PEET’s accuracy.  Currently, PEET has been field validated in Oklahoma and the weed control recommendation treatments from PEET closely match those of OSU Weed Scientists.



  • The use of brand names does not imply endorsement of products nor the exclusion of others.  Brand names are used only for recognition purposes of a herbicide by the producer.

  • PEET should be used with caution in areas outside of Oklahoma where general crop growing conditions, varieties, climate, rainfall, weed species, and soils may differ from areas where PEET was developed and field tested.

  • PEET should only be used as a decision “aid” and not as an absolute for herbicide recommendations.

  • Always read and follow label directions.  Recommendations from PEET do not contain information concerning surfactants, additives, or adjuvants, so follow the manufacturers’ guidelines.

  • Inaccurate inputs may result in poor recommendations.

  • Continue to monitor weed problems after an application, new weed populations may occur.

  • Weed control may vary due to environmental conditions specified on the manufacturer’s label.

INPUT Information/Screens:

PEET consists of an active screen with nine tabs across the top.  The first four tabs require data from the user.  The “Field/Treatments” tab is active upon opening PEET.  The user inputs the appropriate information and moves to the next tab until all information is entered.  The next four tabs supply the herbicide recommendations and the ground water potential hazards based on the user’s inputs.  Following is a step by step pictorial of the tabs explaining the required inputs and the output from PEET.

Field/Treatment: This screen, illustrated below, allows the user to enter a field name and size, for archiving and/or retrieving data at a later date.  Selections of county, soil type, irrigation, and tillage are needed for calculating groundwater hazards of the various herbicides.  Soil texture and organic carbon content also influence the efficacy of some treatments.

This screen, illustrated below, allows the user to enter a field name and size, for archiving and/or retrieving data at a later date.  Selections of county, soil type, irrigation, and tillage are needed for calculating groundwater hazards of the various herbicides.  Soil texture and organic carbon content also influence the efficacy of some treatments.



County:  This is a drop down listing of the counties in Oklahoma where the respective crops are grown.  Simply click on the county and select the appropriate county from the drop-down menu.  Once the county is selected, the Soil Type will default to the soil type most commonly associated with that county.  However, other soil types can be selected from the drop-down menu.  Then the Crop should be selected from the conventional and herbicide resistant crops options.  If a herbicide resistant crop is chosen, treatments displayed in the output will consist of all conventional and specialty herbicide options; i.e. selection of Roundup Ready cotton may result in the display of Roundup (glyphosate) treatments along with Staple, Poast, MSMA, etc. treatments.  However if conventional cotton is selected then glyphosate or Buctril will not be possible treatment options.  NOTE: PEET does not take into account the seed technology fees incurred with purchasing herbicide resistant seed.  Irrigation: the user can select between the most appropriate type of irrigation used on their field.  Treatment: In this example the treatment type chosen was pre-plant incorporated.  There are three or four treatment types depending on the crop selected.  The results displayed by PEET correspond to the selected type of application and any following applications that may occur.  In this case, the results will be displayed for preplant incorporated (PPI), preemergence (PRE), postemergence(POST), and postemergence directed/hooded spray (PDS/HOODED), for cotton.  If POST or PDS/HOODED are selected, the lower box also requires inputs of the soil moisture, approximate weed size (average weed height), and application date.  After this information is entered, move to the next tab by clicking Weeds at the top of the screen.

Weeds: This screen is used to enter the weed species and densities present in the field.  Weed species are listed by common name in weed groups, (i.e. annual grasses, annual broadleaves, etc.) to help the user locate the weed species.  Proper identification and accurate weed densities are essential in order for the user to get meaningful and accurate recommendations from PEET.  Since weeds are not present to determine their densities for PRE treatments, the user can specify densities Low, Medium, or High.  Weed density should be entered in the format of weed numbers/100 sq. ft.  The density levels will be converted to numeric values, using estimates defined in the database by the program developers.  The default numeric values for Low, Medium, and High are species specific.  In the example below the user selected a low density of yellow foxtail, a medium density of rhizome Johnsongrass, and is selecting a high density of common cocklebur.


When entering weed densities for POST treatments, the user should properly scout the field to assess the weed species present and get the most accurate weed densities and heights.  To properly scout the field, the user should take weed counts at several sites (minimum of six) in each field.  Then the weed densities (# / 100 sq. ft.) can be entered for each weed species in the field.

Economics: This screen is used to enter expected yield and market price of the crop, as well as the application and scouting costs.  There are defaults set in PEET for the crop and irrigation type already selected by the user.  The Expected Yields should be the lowest, typical (average), and highest yields expected for that field.

Application costs is the cost the user will incur for one application pass through the field.   If a custom applicator is making the application, then enter the cost the applicator charges for a single application.  The application cost should not include the cost of the herbicide, as the herbicide cost is included in the program.


Prices: This screen is used to enter prices of different herbicides.  Default values are stored in the database, but the user can enter the herbicide prices from their local herbicide supplier.  These values are needed to calculate the treatment cost and determine the economic gain.  The cost of a herbicide plays an important role in the final recommendations and the user should enter the prices that they will pay for the individual herbicides.  The user can save their adjusted herbicide price list (go to file, then “save herbicide data”).  When using the program at a later time, the users can use their prior edited price list (go to file, then choose “load local herbicide data”).


Bar graphs: The figure below presents partial results of a simulation and economic analysis in the form of bar graphs. The list at the center of the figure contains different herbicide treatments and application rates.  Additional bars and treatment descriptions for POST and PDS/HOODED treatments are available by scrolling through the list.


The bar graph on the left shows the estimated economic gain corresponding to each treatment for the weed species and densities specified by the PEET user assuming a weed-free yield of 450 lb/acre.  The user can view the results from the other expected yields by simply clicking on the yield of interest (i.e. 125 or 750 lb/acre) at the top of the screen.  Economic gain is the estimated $/acre the user will gain from using a treatment.  The bar graph on the right shows the groundwater hazard index (on a logarithmic scale) for each treatment.  Together, these bar graphs can be used to select a treatment with a high economic gain and low groundwater hazard.  In some cases, this is not possible so tradeoffs must be made.

The figure below is an alternative form of the bar graph seen above.  In this case the user has chosen to view the expected economic loss due to the weeds after treatment application.  The user can switch between economic gain and loss under the Options tab Here bars are also shown for the case in which no treatment is made. The user can observe the impact of different expected weed-free yields by selecting the yield of interest at the top of the screen.


Economic Gain – Groundwater Hazard Graph: The economic gains and groundwater hazards for each entry are plotted on the Y and X axes, respectively.  The treatment associated with each triangle can be viewed by clicking the triangle of interest.  In this example, the user has selected the triangle in the upper left corner.  The treatment name is displayed in the box under the graph.  The preferred treatment option is one that maximizes economic gain and minimizes environmental hazard, therefore, treatments near the upper left corner of the graph are preferred.  This illustration shows results for Pre-Plant Incorporated treatments and an expected yield of 450 lb/acre.  Results for the other application types and expected yields can be shown by selecting other application types and yields on this screen.


Tabular Output: The output of PEET is also available in a table format as shown below.

Here the treatment type and name are displayed along with the estimated groundwater hazard (%), economic loss ($/acre), economic gain ($/acre), and herbicide cost ($/acre).  This table can be displayed for any of the expected weed-free yields displayed at the top of the table.  The table can be sorted by groundwater hazard, economic loss, economic gain, or herbicide cost.  Sorting allows the user to view the treatment options in increasing or decreasing order, and within or across all treatment types.  To sort, simply click on the Sort Table button in the lower left corner or double click on the column title of interest.  A sort screen will appear, click the button that corresponds to the desired sorting preference.  The table below has the same recommendations sorted by economic gain in decreasing order within treatment type.


Note: Although the estimated gain and loss are displayed to the nearest $0.01 per acre, the model and the parameters used in estimating these values are not that accurate.  Consider any treatments that have economic gains/losses within 10-15% as equals.

Some lines in the table shown above include flags.  This indicates that special instructions or warnings exist for these treatments.  By selecting a particular treatment, a screen opens to provide additional information for that treatment (see in figure below).  This information can also be obtained for all treatments by selecting the “Details/Warnings” tab on the screen.

In addition to the Details/Warnings about the use of the herbicide and a note that other trade names are available for some active ingredients, this screen displays the weed densities and competitive load before and after treatment.  This information can be used to evaluate the need for subsequent treatments.  To change between the treatments, click on the treatment of interest in the column at the right.


Contact D.L. Nofziger at david.nofziger@okstate.edu for more information about this software and its use for other crops and geographic areas.

Last Modified: January 16, 2008

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