Purdue News

February 12, 1999 Planning is the key to saving money on herbicides WEST LAFAYETTE, Ind. -- Picking the right herbicide for your spring crop requires more than just luck. According to Thomas Jordan, professor of weed science in Purdue University's Department of Botany and Plant Pathology, there are many factors to evaluate when selecting herbicides this season. "The most important factor is to keep in mind the weed problems present in your fields and to use the right herbicide for those weeds," he said. Although that may sound simple enough, Jordan said selecting the right herbicide is never easy because of the endless choices of herbicide combinations available for corn and soybean production systems. The problem becomes even more complex when it comes to estimating the cost of various herbicide products. A whole host of factors, including the dealership, time of purchase, quantity of purchase, company guarantees and rebates, can affect the cost of a program. Jordan said that when you add in other factors such as technology fees, application costs and incentive programs for other products such as lime, fertilizer, seed and supplies, direct comparisons between different herbicide programs are difficult -- if not impossible -- to make. Jordan said the best way to estimate costs is to sit down with a dealer, compare options and push the pencil to get the best deal possible. It's important to realize that these estimates will be based on a number of assumptions, such as the planting rate, yields and selling price of the crop. Additionally, Jordan said, several other factors can affect your herbicide costs. For example, he suggested reviewing last year's herbicide program and determining the potential for carryover. If there is potential for carryover, don't use an herbicide with a similar mode of action this year. "Producers should look at the label on the product they used last year," he said. "The label will contain information on rotation restrictions so they can determine if the number of months between the rotations has been fulfilled. For example, if they sprayed in late July or early August last year, later than normal, and their program had a 12-month rotation restriction, they should be aware there is a possibility of crop damage if they plant early." Good agronomic practices that lead to a healthy, well-established, uniform crop stand also will reduce the overall cost of herbicides by shading out late-emerging weeds, according to Jordan. Another cost-control strategy is to control weeds earlier than usual, allowing the use of less than the label's maximum rate of herbicide. Producers using less than the labeled rates of post-emergence herbicides should be prepared to make a second application 10 to 14 days later if the reduced rates were not totally effective. He suggested leaving weeds that emerge after mid-season unless they are extremely large or heavy, because they seldom cause yield losses. "It's best to spray weeds early when they are small," Jordan said. "Producers should try to follow the label of their product and control weeds when they are at the height suggested on their herbicide's label." However, Jordan cautioned against spraying burndown herbicides too early, because the products do not work as well when the temperatures are in the 50s as when the temperatures are 70 degrees or higher. Likewise, he said producers shouldn't spray a post-emergence herbicide when there has been a prolonged dry period and the temperatures are in the high 90s, as this usually causes excessive crop damage and is not very effective in controlling weeds. Producers also should use the correct spray additives with burndown and post-emergence herbicides -- those that are recommended on the product label, Jordan said. Because many products will perform equally as well, Jordan suggested purchasing the cheapest additive. Producers should use AMS, an ammonium salt, with Roundup or other herbicide products that call for this additive on their label, especially when using hard water or water with a high iron content. Jordan also suggested reducing the spray volume to improve herbicide performance on highly mobile herbicides such as Roundup, Select, Past or other grass-specific products. With contact sprays, such as Basagran, Blazer, Cobra or Reflex, Jordan said the higher label-recommended volume should be used for best results. Finally, Jordan said calibrating spray equipment and using proper nozzles to achieve the best coverage and reduce drift can also save money. He suggested periodically calibrating sprayers throughout the season. The majority of sprayers over-apply by 10 percent to 30 percent because of poor calibration and worn tips, he said. Source: Thomas Jordan, (765) 494-4629; e-mail, jordan@btny.purdue.edu Writer: Jane Houin, (765) 494-2722; e-mail, news_students@aes.purdue.edu Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu To the Purdue News and Photos Page