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Corn+Soybean Digest

Do Soybean Fungicides Pay?

Is applying fungicides to corn, soybeans and wheat a good idea? That’s a question many upper Southeast growers will be asking, especially following record fall-winter rain and snow and subsequent damage to thousands of acres of farmland in that region.

Ben Knox, a Mt. Ulla, NC, grower and regional agronomist for the North Carolina Department of Agriculture, says tests on his farm indicate use of fungicides on soybeans can pay.

Knox applied Quadris and Headline to soybeans in small strips on his farm and compared the results with non-treated soybeans. Other than fungicide application, the beans got the same chemical and cultural treatment.

“We harvested the soybeans using a weigh wagon and made one pass through each treatment, harvesting the beans on Nov. 5. Quadris-treated beans produced 56.9 bu./acre, Headline-treated beans produced 56.3 bu./acre and the untreated beans produced 51.8 bu./acre,” Knox says.

The 5-bu./acre bump supports on-farm observations by North Carolina grower Brian Moore. Moore, who farms with his father John Moore, says they typically see a 5-bu. or so yield bump on fungicide-treated beans.

They grow seed beans for UniSouth Genetics, and the fungicides, they say, help them produce the higher-quality seed demanded by the seed industry.

“When you get soybeans up 36 in. or taller at a seeding rate of 120,000-140,000 seeds/acre and you get August rains and humidity that follows, those soybean plants are highly susceptible to disease. Under those conditions is when I think fungicides really help on soybeans,” Moore says.

“Fungicides – like any pesticide – cost money, but at the end of the day, if you can increase yield and quality of your crop, you’re ahead of the game. We grow a lot of our crop for seed, and it’s critical to have good quality and good yield, and we feel like fungicides help us accomplish those goals, Moore adds.

The father and son team uses fungicide on their wheat and barley crops, too. They use it on roughly 75% of their corn crop. They plant corn into heavy bean stubble and keeping more residue on top of the soil is desirable, they say. “Under those planting conditions, using fungicides is a must – we believe they pay off,” says John Moore.

Clearly, fungicides paid off last year as the Moores were second in the Piedmont Region in the North Carolina Wheat Yield Competition with an on-farm average of 82 bu./acre. First place winner Travis Starnes, with 88.7 bu., also treated his wheat with fungicides.

Despite the on-farm success, researchers aren’t convinced routine application of fungicides increases yields on soybeans in particular. To increase the chances of yield bump, the consensus seems to be to follow at least four standard keys before applying fungicides:

  • Know the susceptibility of the soybean variety you are planting. Susceptibility to frogeye leaf spot and other common diseases of soybeans can usually be obtained from the seed company. Another often used source of variety information comes from the Variety Information Program (VIP) database.
  • Know the crop history of a field. Many foliar pathogens of soybeans survive in soybean stubble. The more stubble present on the soil surface the higher the risk of foliar diseases in soybeans. With such a high percentage of soybeans in the upper Southeast being planted in no-till, double-crop systems many fields are at risk, but not all.
  • Wet soybean leaves, regardless of the source of moisture, produce a favorable environment for fungal pathogens to develop and for disease to occur. Conversely, hot and dry leaf surface significantly suppresses disease development.
  • Understand soybean rust risk. Though rust has not been a significant problem for upper Southeast soybean farmers, the risk still exists. More importantly which family of fungicides used and when these materials are used is significantly affected by the threat of soybean rust.

University of Kentucky Plant Pathologist Don Hershman says growers should consider the risks before applying fungicide to crops because its effects are unpredictable and in many cases, applications are not warranted.

"Historically, corn and soybeans are not grown under conditions that favor the development of foliar fungal diseases – the primary target of fungicide applications. Most acreage being treated in Kentucky does not need it for disease control," the Kentucky researcher says.

"Some fungicides have produced higher yields compared to non-treated crops in the absence of disease, but university research trials indicate that statistically higher yields are produced only about 25-30% of the time when disease is not a factor," Hershman adds.

Veteran North Carolina State soybean specialist Jim Dunphy says farmers considering using fungicides on soybeans have some pros and cons to consider.

The downside of fungicide application is the cost of the fungicide and application. The upside is protection from disease – preventing yield loss and protecting the crop.

Reasons to apply fungicides:

  • Presence of disease (frogeye, target spot, anthracnose).
  • High yield potential.
  • Premium for seed quality.
  • Consider how long it will take to get a fungicide applied to needed acreage. Take into consideration that with wet conditions you may not be able to apply by ground. Also, consider that application at R5 with a strobilurin or Topsin M can protect seed quality if harvest is delayed.

Reasons not to Apply Fungicides:

  • Cost.
  • Soybean at or beyond growth stage R5.
  • Increased potential for development of a fungicide-resistant disease.

The bottom line, Dunphy says is North Carolina soybean growers must be making good decisions. North Carolina soybean producers harvested 34 bu./acre in 2009, tying the record set in 2004. A record 60,180,000 bu. were harvested from 1.77 million acres.

“The outstanding production reflected good growing conditions for much of the season, with excess moisture impacting only late season growth and, of course, the harvest,” Dunphy concludes.

There is not an across-the-board answer to whether or not using fungicides on soybeans will pay. How well fungicides will pay off on soybeans depends on a lot of factors that can only be answered by an individual farmer and usually on a field to field basis.

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