Weeds are calculating organisms, always looking to make life difficult for farmers. To defeat the unwanted plants, producers have to be twice as calculating. Growers can start with two free computer calculators.

The Web-based tools are programs within WeedSOFT, a weed management software package developed by Purdue University and eight other land- grant universities. While the entire package must be purchased, the WeedSOFT team decided to provide with farmers two programs online at no charge, said Bill Johnson, Purdue Extension weed specialist.

The yield loss and tank mix calculators are being offered free to help producers avoid weed-related crop losses as well as introduce them to WeedSOFT, Johnson said. The calculators are available at http://weedsoft.unl.edu/WeedsoftApps.htm.

"As more and more growers plant Roundup Ready corn there's a tendency to delay herbicide applications until the weeds have quite a bit of size on them," he said.

"Most of us in the weed science world have felt that we're leaving an awful lot of bushels in the field by delaying these spray applications. So we felt by taking the WeedSOFT yield loss calculator out of the program and making it free and available on the Web, that growers would be in a position to make better decisions as far as timing post-emerge sprays to minimize yield loss due to weed competition."

The yield loss calculator projects likely crop reduction based on the crop planted, the crop's growth stage, the weeds growing in the field and other factors.

"We've set up a system where a grower can enter the weed density, the weed size and their expected yield, and they will get a yield loss estimate from WeedSOFT," Johnson said. "Then they can decide whether they are making the appropriate decisions on when to spray post- emergence herbicides."

The tank mix calculator aids in selecting the type and amount of herbicide needed to treat a field, Johnson said.

"This calculator allows a grower to enter the size of their field, the size of their spray tank, their desired herbicide rate and their sprayer carrier volume, and then put the appropriate amount of spray or additives within the spray tank," he said. "Many of the questions I get from growers relate to herbicide injury or inadequate weed control, and we felt that having a calculator like this available for growers might minimize some of the mistakes that are made in the mixing process."

Farmers who purchase the WeedSOFT package receive other helpful resources, Johnson said.

"WeedSOFT includes not only these calculators but also specific recommendations for what products to use to control specific weeds," he said. "WeedSOFT also contains a weed identification module and some modules which allow you to keep very detailed records on what you spray for specific weed infestations. In addition, it also has an environmental module, which allows you to separate the products that you may use based on their potential to contaminate surface or groundwater."

The software program's 2006 version offers a handful of new features, including weed management for hay crops.

First-time users can purchase WeedSOFT for $50, while annual updates are $40.

To learn more about WeedSOFT or to order the software package, log onto the product Web site at http://weedsoft.unl.edu.

In addition to Purdue, other WeedSOFT collaborators include the universities of Illinois, Missouri, Nebraska and Wisconsin; and Kansas State, Michigan State, Ohio State and Penn State universities.

The original WeedSOFT was introduced in Nebraska in 1992.