Spraying fungicides at R1, R3 on soybean

decrease font size  Resize text   increase font size       Printer-friendly version of this article Printer-friendly version of this article

Across Iowa many growers are starting to ask if or when to apply fungicide on soybeans in 2011. There are essentially two options being discussed. The first is to apply fungicides at R1 (flowering). This application could be tank-mixed with the last application of glyphosate. The second option is to apply fungicide at R3 during pod formation. This application could be tank-mixed with an insecticide or applied alone. Which application timing is best? Which products best protect yield?

To answer these questions we conducted soybean fungicide trials at various locations in Iowa from 2008-2010. We evaluated the yield response of soybeans to applications of a strobilurin (Headline), a triazole (Flusilazole or Domark) and a premix of strobilurin + triazole (Stratego YLD). We also assessed foliar disease severity at R5. Finally we calculated the probabilities that an aerial application of a fungicide product would “break even” at a specific site year when prices of beans were estimated at $10, $13, and $16 per bushel. The cost of fungicides was estimated using information gathered from area cooperatives and field agronomists.

Our results are summarized in Table 1. 

  • In all years, disease severity was low. 
  • Brown spot was the most common disease and was found virtually only in the lower canopy. 
  • The yield response of soybeans was greater with an R3 application rather than an R1 application. So, an R3 application of a fungicide was more likely to break even than an R1 application
  • The chance that an R3 application of a fungicide would break even ranged from 7 to 99 percent.
  • Products that contained a strobilurin as one of the active ingredients were more likely to  break even compared to a product containing only a triazole. 

click image to zoom Spray when disease could impact yield

Although these data suggest that nearly 60-70 percent of R3 applications of a fungicide containing a strobilurin at least break even, spraying when disease is present will further increase your chances of getting your money back. If brown spot remains in the lowest third of the soybean canopy – it probably will not impact yield. If the disease moves into the middle third of the canopy, brown spot can start to reduce yield. We saw this at one of our locations in 2010. At that location, the mean yield response due to a fungicide application at R3 was nearly double the responses at other locations (5-6 bu/ac vs 2-4 bu/ac).  

Resistance to fungicides reported in 2010

A caution when spraying fungicides – scout fields after applying the fungicides and look for applications that do not appear to affect disease severity. In 2010, resistance to the strobilurin fungicides (Headline, Quadris, one of two active ingredients in Stratego YLD and Quilt) in the fungus that causes frogeye leaf spot was reported in Tennessee, Kentucky and Illinois [University of Illinois].

Funding for this project was provided by the Iowa Soybean Association, Bayer CropScience, DuPont, Valent and BASF.

Buyers Guide

Doyle Equipment Manufacturing Co.
Doyle Equipment Manufacturing prides themselves as being “The King of the Rotary’s” with their Direct Drive Rotary Blend Systems. With numerous setup possibilities and sizes, ranging from a  more...
A.J. Sackett Sons & Company
Sackett Blend Towers feature the H.I.M, High Intensity Mixer, the next generation of blending and coating technology which supports Precision Fertilizer Blending®. Its unique design allows  more...
R&R Manufacturing Inc.
The R&R Minuteman Blend System is the original proven performer. Fast, precise blending with a compact foot print. Significantly lower horsepower requirement. Low inload height with large  more...
Junge Control Inc.
Junge Control Inc. creates state-of-the-art product blending and measuring solutions that allow you to totally maximize operating efficiency with amazing accuracy and repeatability, superior  more...
Yargus Manufacturing
The flagship blending system for the Layco product line is the fully automated Layco DW System™. The advanced technology of the Layco DW (Declining Weight) system results in a blending  more...
Yargus Manufacturing
The LAYCOTE™ Automated Coating System provides a new level of coating accuracy for a stand-alone coating system or for coating (impregnating) in an automated blending system. The unique  more...
John Deere
The DN345 Drawn Dry Spreader can carry more than 12 tons of fertilizer and 17.5 tons of lime. Designed to operate at field speeds up to 20 MPH with full loads and the G4 spreader uniformly  more...
Force Unlimited
The Pro-Force is a multi-purpose spreader with a wider apron and steeper sides. Our Pro-Force has the most aggressive 30” spinner on the market, and is capable of spreading higher rates of  more...
BBI Spreaders
MagnaSpread 2 & MagnaSpread 3 — With BBI’s patented multi-bin technology, these spreaders operate multiple hoppers guided by independent, variable-rate technology. These models are built on  more...

Comments (0) Leave a comment 

e-Mail (required)


characters left

Aluminum Grain Trailers

Maurer Manufacturing offers a complete line of high quality aluminum grain trailers. Manufactured in Spencer, Iowa, Maurer aluminum grain trailers ... Read More

View all Products in this segment

View All Buyers Guides

Feedback Form
Feedback Form