Peanut fungicide: Is this the year to go with generics?

Bob Kemerait, UGA Extension Plant Pathologist | Southeast Farm Press

This will become the most frequently asked question of my 2016 field season: “What is the best fungicide program for peanuts this year?” 

Following 2015, when diseases like white mold (stem rot) were especially troublesome in many fields and looking ahead into the 2016 season, when growers are struggling for a profitable peanut crop, finding the “best” fungicide program is critical.

There are a number of components to a best fungicide program.  Some growers consider cost to be the single-most important factor in deciding on the fungicide program. While attending the Peanut Efficiency Award session at last year’s Southern Peanut Growers’ Conference, I asked the winning growers, “How do you decide upon the best program for your production system?” 

The first grower said he had developed a good relationship with his local Extension agent and also representatives from the agrichemical industry. The second grower’s answer caught me off guard, especially considering industry sponsorship is a much-appreciated part of the conference. 

In response to my question, he said, “I don’t need any more jackets or hats. My decision for a fungicide program is largely based on cost and the best-priced fungicides are typically ‘generic’ products.’”  His answer was blunt and honest.  Given his success, it was tough to argue about his decision process when he had just been awarded for his farming operation. 

While there is no doubt that generic/off-patent fungicides can provide significant value to a disease-management program, there are other factors that are equally important to price when picking the best program. These factors add value to the fungicide program beyond the dollars and cents spent at the retailer.

The first consideration for choice of fungicide must be efficacy.  Some fungicides are simply better at controlling important diseases than are other fungicides. The molecules that form the active ingredient of one fungicide may be more effective against a disease-causing pathogen than other even closely related molecules.  Chemistry IS important, despite what many high school and college students feel today. 

Other aspects that make one fungicide more effective than another include the interaction of the fungicide with the plant (curative versus protectant), physical properties that add to performance. For example, how well a fungicide is able to avoid degradation upon application, and how well a fungicide can be redistributed on the whole plant for maximum protection.

The second important consideration is mode of action, that is, the process by which a fungicide attacks a disease-causing pathogen.  Resistance results when a fungicide (or class of fungicides) that used to be effective in managing a disease becomes less effective (require increasing rates of product) or is no longer effective even at highest rates. 

Peanut growers as whole can prevent, or at least delay, the onset of fungicide resistance by using fungicides appropriately, i.e., good timing of applications and at correct rates, and by following guidelines to avoid overuse of a fungicide or class of fungicides.  Some growers have told me that while using good practices to maintain efficacy of fungicides is important to them, they often feel pressured to “get through this season.” This can lead to practices that increase risk for resistance. 

Peanut growers are no strangers to fungicide-resistance issues.  Leaf spot pathogens have developed resistance to benzimidazole fungicides such as benomyl and thiophanate methy.  Resistance has also developed to tebuconazole and some believe is soon to be found in strobilurin fungicides as well.  Mixing fungicides with different modes of action to protect against fungicide resistance is often requires products from the major agrichemical companies.  Use of such products is important for continued management of peanut diseases into the future.

A final consideration has to do with the future of fungicides available for peanut production.  It is estimated that a company must screen approximately 250,000 molecules in order to find one that will eventually be labelled and sold as a commercial fungicide.  This process takes at least 10 years and as much as $250 million.  Considering that the company must patent the product in the early stages of development and that a patent typically expires after 17 years, decision makers must carefully decide whether to pursue a new fungicide or not. 

Given that peanut is a “minor” crop in the United States, the decision to bring new fungicides to market becomes an even more difficult one, especially if an inexpensive generic fungicide is already available.  However, the availability of new fungicides with improved modes of action is critical for the future of the peanut industry.  Including non-generic fungicides in a complete program is an investment not only for this season but also for seasons to come.

There is no single “best” program.  White mold can be severe in a non-irrigated field with a history of disease as irrigation (and rain) is important for redistribution of the product to protect the crown of the plant.  Given the yield potential of a non-irrigated field, use of a generic product like tebuconazole is appropriate. But for the reasons mentioned above, the grower is also best served to include “name brand” products in the program with better efficacy that will improve profitability at harvest.

Source: Southeast Farm Press