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Issue No. 6, Article 8/May 5, 2006

Fungicides and Soybeans: When Should You Use Them?

Wading through the mire of fungicide information is a new task for Illinois producers and applicators. To date, use of foliar fungicides in soybean production in central Illinois has been virtually nonexistent. The introduction of soybean rust to the southeastern United States has changed the outlook for fungicide use dramatically. Before you invest any money in fungicides for the upcoming production season, let's be clear about some significant issues.

First, let's jump into the legal territory. As you have heard me repeat at pesticide safety training and testing sessions for many years, the label for a pesticide is a legal document. That means whether the pesticide is a general or a restricted-use product, the applicator is obligated to follow the label. Fungicides that have a full legal label for use are described as having a Section 3 label. In Illinois, we actually have had very few fungicides with a Section 3 label for use in soybean for control of fungal leaf or stem diseases. A list of these can be found in the 2006 Illinois Agricultural Pest Management Handbook. They are azoxy-strobin (Quadris), chlorothalonil (Bravo and numerous brands), thiophanate-methyl (Topsin-M), and recently pyraclostrobin (Headline).

Why am I bringing up this issue? Well, when soybean rust was identified in the United States, numerous states applied for emergency use permits for triazole and triazole/strobilurin combination fungicides to control it. This kind of emergency label is called a Section 18. The EPA granted numerous Section 18 labels for these states, including Illinois, thus allowing the use of those products "in soybean, specifically for management of soybean rust." For the most part, the Section 18 labels have been granted through 2007, with some recent additions through 2009. The EPA would expect that, during the interim, companies that have been granted Section 18 labels would complete the process to apply for full Section 3 labels.

As soybean rust gains momentum in the south, we are well aware that the probability of infection for Illinois increases. Growers want and need information on these Section 3 and Section 18 fungicides relevant to Illinois conditions. As a result, researchers and pesticide industry individuals initiated research in the 2005 season to look at the effect of these many products on soybean rust. The research went forward regardless of the fact that soybean rust did not impact Illinois in 2005.

Information gleaned from these studies can be confusing. Some products did economically manage current diseases we have in Illinois; others, however, resulted in economic loss, and some were break-even economically. This is interesting from the point of view of managing current Illinois fungal diseases. However, you must exercise caution in adapting these findings to your soybean production. Prior to the actual identification of soybean rust in Illinois, the only fungicides you can use to control our current fungal diseases are the Section 3 products I've previously mentioned.

If Asian soybean rust gets to Illinois, applicators will have a much larger selection of fungicides available to them to manage the disease, including Section 3 and Section 18 products. Well, when can you use a Section 18 product labeled for Asian soybean rust? The Illinois Soybean Rust Taskforce, headed by Jim Larkin of the Illinois Department of Agriculture, dealt with this important issue this spring to clarify for soybean fungicide users in Illinois who may need to spray to manage Asian soybean rust. Warren D. Goetsch, P.E. Bureau Chief, Environmental Programs, Illinois Department of Agriculture, has outlined the department's stance on the issue, as follows.

"In response to the question regarding when it would be legal to apply a FIFRA (Federal Insecticide, Fungicide and Rodenticide Act) Section 18-labeled fungicide for possible control of Soybean Rust: With regard to the creation of some type of definition for 'imminent threat of soybean rust' or some other type of triggering mechanism, the Illinois Department of Agriculture does not believe that such a definition or trigger is necessary. Growers and/or crop consultants make important pest management decisions all across the fields of Illinois almost every day during the growing season. Determinations regarding pesticide applications associated with Soybean Rust control treatments should not be considered any differently.

"Therefore, it is the position of the Illinois Department of Agriculture, as the state lead agency for the administration of the FIFRA in Illinois, that growers can choose to make label-consistent applications of Section 18-registered fungicides onto soybeans at any time such application would be consistent with the provisions of the product label. In other words, if a grower believes that the use of one of these products would be beneficial in combating a possible outbreak of Soybean Rust in his or her specific production field and the product is appropriately registered and labeled, the grower is free to use the product as the label instructs. As with any pesticide, the use of fungicides which have been registered with the U.S. EPA and the Illinois Department of Agriculture must always be conducted consistent with the provisions of the product label. As the current Section 18 product labels indicate, these products are intended for the control of Asian Rust on Soybeans. Use for any other purpose is not allowed."

We have a large number of Section 3- and Section 18-labeled fungicides available for management of soybean rust in Illinois, as listed in Table 1 (Adobe PDF, 72 KB). With timely and appropriate application they are good tools for economic rust management.

Author:
Suzanne Bissonnette

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