Weed Tools on the Web

Chris Boerboom, Ext. Weed Scientist

Two handy weed management tools are available on the web at http://weedsoft.unl.edu (just click tools on the top menu).  The first tool is a “WeedSOFT Yield Loss Calculator” that predicts corn or soybean yield loss from single or multiple weed species.  Basically, it predicts early season weed competition.  On the first screen, enter the crop information (crop, stage, expected yield, and price) and weed information (species, density, and size). A click of the “calculate” button will present the predicted results of the weed competition, if the weeds were not controlled, if controlled at the indicated crop stage, and if control was delayed until the next crop growth stage.  Results are given in both bushels lost and in dollars lost.

This is a neat tool, but why would a person be interested in using it?  Probably the best reason for using the tool is to evaluate the potential consequences of delayed postemergence herbicide applications.  It certainly cheaper to simulate and evaluate the results of applications made at different crop or weed stages than to suffer the real-life yield loss from a delayed application in a 40 acre field.  So, for a set of weeds that you might expect in your field, you can test and see when early season weed competition starts to kick in.  Then, you can consider if there is a risk of not getting weeds controlled by that time or not.  If there is too much risk, it might be time to consider alternate management plans.

Another time to use the calculator might be in re-spray situations where you want to determine if a weed’s density is greater than the economic threshold.  Does the yield loss exceed the cost of the herbicide and application?

Finally, the calculator’s total predicted yield loss without control certainly demonstrates the great return in investment that we gain from weed management programs, even though we still like to complain about their cost.  We certainly make a huge return on this investment in producing our crops and sometimes we may forget about that fact.    

Ag teachers might also be interested in using the calculator to illustrate weed management principles such as that weeds differ substantially in how competitive they are or that late emerging weeds (small weeds in large crops) are less competitive than early emerging weeds.

The second tool is a “WeedSOFT Tank Mix Calculator” that doubles as a herbicide record keeping form.  If you have ever been unsure about calculating the amount of herbicide to add to your sprayer, this might be just the tool for you.  With herbicide labels recommending rates as fluid ounces, dry ounces, pints, and quarts, it can sometimes be confusing.  And you certainly don’t want to make a mistake because it can be costly.  An error that under calculates the amount of herbicide needed for a spray load might lead to poor weed control.  A calculation mistake that leads to adding too much herbicide to a sprayer is wasted money or may lead to crop injury.   

In the tank mix calculator, a screen opens where herbicides, adjuvants, their rates, your spray rate, spray tank size, and field size are selected with a few simple clicks or key strokes.  Two important steps are to click “Add herbicide” after each herbicide and rate is selected and to click “Calculate” after all herbicides and adjuvants are entered.

The tool calculates the amounts needed and enters the information on the next screen, which is a “Load Ticket”.  The load ticket lists the calculated amount of each herbicide and adjuvant required for each spray load (and partial load if needed) to spray the field.  This page can be printed and taken to the yard or field to mix spray loads. 

The load ticket can also serve as your record keeping form if desired.  Just write in your personal, application, and field information.  Then, you have a herbicide record that satisfies Wisconsin record keeping requirements.  (Information on wind, temperature, and re-entry interval (REI) are not state required information, but may be useful to record).

One final comment; remember to calibrate your sprayer.  These calculations will only assist with getting the right rate sprayed in the field if your sprayer is calibrated.