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Foliar Fungicide and Insecticide Effects on Soybean Yield

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Summary

  • Pioneer Agronomy Sciences researchers conducted trials from 2004 to 2008 to evaluate the effects of foliar fungicide and fungicide/insecticide applications on soybean yield.
  • Despite considerable variation in growing conditions across years and locations, the trials demonstrated a consistent positive yield response to treatments that included strobilurin fungicides (Headline® and Quadris®).
  • These fungicides, when used alone or in combination with insecticides, increased soybean yields by 2.9 to 5.5 bu/acre on average.
  • The strobilurin-only treatments were economically beneficial in nearly half the trials, but adding an insecticide increased the profitable trials to about two out of three.
  • Trials conducted at three locations in 2008 gave results similar to the five-year trials as a whole.
Positive results by growers continue to drive more use of foliar fungicides on soybeans.

Positive results by growers continue to drive more use of foliar fungicides on soybeans. (Photo courtesy of Case IH.)

Introduction

The increased grain price of soybeans has made crop inputs such as foliar fungicides more attractive to growers. In addition, the possibility of physiological benefits to the plant from strobilurin fungicides (Headline and Quadris®) has generated interest in these products. As a result, foliar fungicide use has increased in most soybean-producing states.

Pioneer Agronomy Sciences research conducted over five years has shown fairly consistent yield increases of over three bu/acre on average from strobilurin fungicides. Although leaf diseases are often present in these plots at some level, most are thought to have minimal, non-economic impacts on yield. This leads to the possibility that physiological benefits apart from disease protection often claimed for these fungicides may indeed play a role in increasing soybean yields. These benefits may include reduced ethylene production, improved CO2 assimilation, increased water use efficiency, increased stress tolerance during flowering and pod fill and delayed plant senescence. Whether higher yields are from some combination of these physiological effects or control of previously ignored foliar diseases, the positive results achieved by growers continue to drive more use of foliar fungicides.

Insecticide applications to soybeans have also increased in recent years due to soybean aphid proliferation throughout most of North America. However, unlike claims for fungicide products, insecticide benefit in the absence of pests has not been heavily promoted. Nevertheless, more growers are exploring the benefits of increased insecticide use, particularly by including an insecticide in the tank when making a fungicide application. Although this practice is efficient from an application standpoint, growers should be aware that precise timing is usually required for optimum effectiveness of one or both spray components.

The objective of this study was to evaluate the effect of the strobilurin fungicides Headline and Quadris, a triazole fungicide, Punch®, and fungicide/insecticide combinations applied at soybean growth stage R3 to R4 (pod stages) on soybean yield. This study builds on four previous years of fungicide/insecticide research initiated in 2004 by Pioneer Agronomy Sciences.

 

Study Description

Replicated trials were planted at four locations in the 2008 Pioneer study (Table 1).

Table 1. Locations, planting dates and varieties included in the 2008 Agronomy Sciences fungicide/insecticide study.

Location Planting Date   Maturity Group  Pioneer® brand Soybean Varieties
Mankato, MN April 30 II 92M21(RR), 92Y30(RR), 92M32(RR), 92M40(RR)
York, NE May 1 III 93M11(RR), 93Y20(RR), 93M42(RR), 93M43(RR)
Champaign, IL   May 5 III 93M11(RR), 93Y20(RR), 93M42(RR), 93M43(RR)
Tipton, IN May 28 III 93M11(RR), 93Y20(RR), 93M42(RR), 93M43(RR)

Trials were planted in 30-inch rows at 160,000 seeds/acre. Eight treatments were applied at soybean growth stage R3 to R4, the pod development stages (Table 2). Fungicides and insecticides were applied at labeled rates in a total volume of 15 to 20 gallons/acre. Soybean yield was recorded. Data were analyzed using an ANOVA for split-plot arrangement of a randomized complete block design.

Table 2. Treatments used in 2008 fungicide/insecticide study.

Treatment Code*  Fungicide Growth Stage  Rate/Acre
CHECK Untreated Check    
HEADR3 Headline® R3 to R4 6 oz
QUADR3 Quadris® R3 to R4 6.2 oz
PUNR3 Punch® R3 to R4 4 oz
H/ASR3 Headline +Asana®  R3 to R4 6 oz and 6.4 oz
Q/WR3 Quadris+ Warrior® R3 to R4 6.2 oz and 2.56 oz
P/ASR3 Punch + Asana R3 to R4 4 oz and 6.4 oz
ASANA Asana R3 to R4 6.4 oz

* Treatment codes are used in the graphs.

Results

Grain yield averaged across varieties at the Maturity Group III locations.

Figure 1. Grain yield averaged across varieties at the Maturity Group III locations in the 2008 foliar fungicide study.

The response was different at the Group II location due to high soybean aphid pressure in the plot which reduced yields of the check and most fungicide-only plots to near 50 bu/acre. Highest yields were achieved by application of an insecticide or fungicide/insecticide combination. Asana applied alone increased yield by 20.5 bu/acre, Headline + Asana by 24 bu/acre, Punch + Asana by a 23 bu/acre, and Quadris + Warrior by 18.2 bu/acre at the Group II location (Mankato, MN).

Has the response to foliar fungicide and insecticide treatments been consistent across years?
Yes. Though conditions have varied widely across years and locations, numerous comparisons over the past five years have demonstrated a consistent positive yield response to strobilurin fungicide and insecticide treatments (Table 3).

Table 3. Average yield response for fungicide and insecticide treatments evaluated in 2004 to 2008 studies.

Treatment Years Tested N+ Yield Response (bu/A)
Headline R1 2007 40 2.3
Headline R3 2004-08 100 3.7
Quadris R3 2004-08 100 2.9
Folicur® R3 2004-06 48 1.5
Quadris/Warrior R3 2005-08 88 4.1
Headline/Asana R3 2007-08 52 5.5
Headline R5 2004-06 48 2.7
Quadris R5 2004-06 48 1.6
Headline R3+ R5 2004-06 48 4.6

How often is there an economic yield response from a foliar fungicide or fungicide/insecticide application under Midwest conditions?

This research has shown that applying a strobilurin fungicide with or without an insecticide at growth stage R3 to R4 frequently results in a significant yield response. The graphs that follow illustrate whether the yield gains are enough to be economical and how often a positive response is obtained. Values above the red line represent a positive return on investment (i.e. an economic response). For simplicity, the treatment cost (fungicide + application) per acre was estimated at the value of three bushels of soybeans. Results show that:

 

  • Headline® applied at the R3 stage resulted in an average yield response of 3.7 bushels/acre. A positive yield response was observed 78% of the time and an economic yield response 51% of the time (Figure 2).
  • Quadris® applied at the R3 stage resulted in an average yield response of 2.9 bushels/acre. Although the average yield response was lower than Headline, the positive and economic yield responses were very similar (Figure 3).
  • Quadris/Warrior® applied at the R3 stage resulted in an average yield response of 4.1 bushels/acre. A positive yield response was observed 77% of the time and an economic yield response 59% of the time (Figure 4).
  • Headline/Asana® applied at the R3 stage resulted in an average yield response of 5.5 bushels/acre. A positive yield response was observed 90% of the time and an economic yield response 73% of the time (Figure 5). This treatment was only evaluated in 2007 and 2008.

    • Chart: Yield response to Headline (2004-08)

    Figure 2. Yield response to Headline (2004-08).

    Chart: Yield response of Headline/Asana (2007-08)

    Figure 4. Yield response of Headline/Asana (2007-08).

    Chart: Yield response to Quadris (2004-08)

    Figure 3. Yield response to Quadris (2004-08).

    Chart: Yield response of Quadris/Warrior (2005-08)

    Figure 5. Yield response of Quadris/Warrior (2005-08).

    RR=Contains the Roundup Ready trait. ® Roundup Ready is a registered trademark used under license from Monsanto Company.

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