By Russell Hood and Bob Ratliff

MISSISSIPPI STATE -- Choice is usually a good thing, but sometimes a person doesn't have the time or information to make the right decision, whether it be choosing a flavor of ice cream or the best weed-control method.

So it is with soybean producers making herbicide application decisions, which can be a daunting task even for weed scientists who deal with the subject daily. Producers, who must focus the majority of their time on other production concerns, can easily be overwhelmed by the decisions and choices available. Weed-control decisions for soybeans are complex and challenging because of factors such as weed species, herbicide effectiveness and cost.

Mississippi State University weed scientists have adapted an expert computer decision aid to evaluate all these factors and help producers, Extension personnel and private consultants evaluate potential crop damage from weeds. The aid then determines if a herbicide treatment is economically justified and, if so, selects an appropriate herbicide and application rate.

Named MSU-HERB (short for herbicide), the program provides an efficient way to give out a large amount of complicated information in a manner to simplify herbicide application decisions.

The software evolved from the HERB soybean weed-control computer model developed at North Carolina State University in the 1980s. Dr. David Shaw, a weed scientist with the Mississippi Agricultural and Forestry Experiment Station, and Dr. John Byrd, associate weed specialist, refined HERB for Mississippi growing conditions.

"The program works really well if good data is put in. You have to incorporate common sense into the program," Shaw said.

HERB and Soybean Weed Control, developed at the University of Arkansas, were designed to aid producers in determining an economical and effective herbicide treatment for weed control in soybeans.

The Mississippi Soybean Promotion Board funded Shaw and Byrd's first research project. HERB and SWC models were run at different locations and the models generated recommendations. The researchers would also make and compare their own recommendations with the models, including weed-control methods and costs involved.

Shaw said HERB and SWC did as well as or better than the human-generated recommendations. Although both models did overestimate yield loss in some instances, HERB had less variability when they compared the actual to predicted losses.

Shaw and Byrd then used a program that allowed them to modify the database that HERB uses in calculations. They were able to adjust the competitive index for each weed and weed control from each herbicide, as well as add new weeds and herbicide treatments, to better reflect Mississippi conditions.

In subsequent field tests during a 3-year period, researchers went back to the field to compare the old HERB to the new version to determine if adjustments were valid.

"Performance was fairly comparable. But any time there was a difference, the advantage went to the MSU version, so we felt like the adjustments were warranted," Shaw said.

MSU-HERB ranks weeds from 0 to 10 based on competitiveness of the weed with soybeans and ranks herbicides on their ability to control weeds.

The model predicts the yield loss associated with each weed and the effectiveness of each herbicide for improving yield. The computer model contains about 75 weed species and about 45 herbicide options; additions are in the works.

"It is a fairly small program," Shaw said. "We use a laptop in the truck and can run the model in the field when we are ready to spray. With a printer, the program will generate a written report on why it made specific recommendations. This gives the consultant or Extension agent written justification for why a decision was made, and is also a great record-keeping tool."

In addition to the economic benefit MSU-HERB provides users, the program also helps protect the environment because only as much herbicide as is needed is used, and decisions are based objectively on herbicide efficacy and weed threshold concepts.

The soybean herbicide recommendation computer software program is available for use at no charge to farmers at all county Extension offices, or they may obtain copies by contacting Byrd.