Evaluation of Foliar Fungicides on Soybeans in 2018

February 11, 2019
ICM News

Soybean foliar fungicides were evaluated for foliar disease management and yield response across seven Iowa State University research and demonstration farms in 2018. These included the Northwest Research and Demonstration Farm (Sutherland), Northern Research and Demonstration Farm (Kanawha), Northeast Research and Demonstration Farm (Nashua),  Central Iowa Research Farms (Ames), Armstrong Memorial Research and Demonstration Farm (Lewis), McNay Memorial Research and Demonstration Farm (Chariton), and Southeast Research and Demonstration Farm (Crawfordsville).

Field experiments at each location were laid out in randomized complete block design with four replications. Plot size ranged from 25.5 to 40 ft long and 10 to 15 ft wide (4 rows 30-inch inter-row spacing). Soybean cultivar and additional details are listed in Table 1. A total of 18 fungicide products were applied at recommended rate (Table 2) with a self-propelled research sprayer at growth stage R3 (beginning pod) at all seven locations. Foliar diseases were assessed when soybeans reached at the R6 (full seed) growth stage. Septoria brown spot (caused by Septoria glycines) progression was assessed by measuring the height of the highest infected leaf and determining disease severity by estimating the percent of leaf area covered by the disease on 10 leaves in the upper canopy. Other foliar diseases were also assessed, including frogeye leaf spot (caused by Cercospora sojina). Total seed weight/plot and moisture were measured with a 2009 Almaco SPC20 research plot combine. Seed weight was adjusted to 13 percent moisture and yield was calculated.

Table 1. Research location, cultivar, planting date, planted population, fungicide application (spray) date, disease assessment date, and harvest date for seven soybean fungicide trials throughout Iowa in 2018.

Research Location

Ames

Armstrong

Crawfordsville

Kanawha

McNay

Nashua

Sutherland

Cultivar

28-N6

28-N6

28-N6

28-N6

28-N6

28-N6

28-N6

Planting date

5/17/18

5/9/18

5/23/18

5/29/18

4/30/18

5/20/18

5/19/18

Planted population

140,000

150,000

165,000

150,000

149,000

175,000

140,000

Fungicide application date

7/24/18

7/23/18

7/16/18

7/30/18

7/23/18

7/31/18

7/26/18

Disease assessment date

9/3/18

9/6/18

8/30/18

9/5/18

.

8/30/18

9/6/18

Harvest date

10/20/18

10/24/18

10/25/18

10/23/18

10/25/18

10/23/18

10/24/18

 

Table 2. Fungicide products and their application rate for seven soybean fungicide trials throughout Iowa in 2018 *All products were applied at R3 with nonionic surfactant (Induce at 0.3% v/v) unless otherwise noted. *All Group 11 fungicides are QoI's.

Product

FRAC group

Rate (fl oz/A)*

UTC

..

 

Aproach

11

6 oz/A

Aproach Prima

3+11

6.8 oz/A

Delaro

3+11

8 oz/A

Domark 230

3

6 oz/A

Fortix

3+11

5 oz/A

Lucento

3+7

5 oz/A

Miravis Neo

3+7+11

13.7 oz/A

Preemptor

3+11

5 oz/A

Priaxor

7+11

4 oz/A

Quadris

11

6 oz/A

Quadris Top

3+11

8 oz/A

Quilt Xcel

3+11

10.5 oz/A

Stratego YLD

3+11

4 oz/A

Topguard EQ

3

5 oz/A

Trivapro

3 + 7+ 11

13.7 oz/A

Viathon

3+33

23 oz/A

Zolera FX

3+11

5 oz/A

 

Result summary

Overall, the northern and northeastern experiment locations received more precipitation than the other sites. However, a large amount of rainfall occurred during the months of August and September in many locations. This is important to note as August is the critical month for foliar disease development. Frogeye leaf spot was observed at greater levels in all the locations compared to previous years. This might be due to a combination of Quinone outside inhibitors (QoI) fungicide resistant strains of C. sojina, which were confirmed throughout the state in 2017, coupled with the high rainfall in August. Septoria brown spot was also observed at all locations.

Heavy rainfall in September and October challenged timely harvest in many locations. Average yield in untreated plots was 54.9 bu/A. Yield response to fungicide was statistically significant, and the yield response ranged from 0.8 to 7.4 bu/A (Figure 1).

2018 yields after application
Figure 1. Soybean yield response to fungicide products combined across all seven experiment locations in 2018. Means followed by the same letter are not statistically significant from one another.

Treatment effect was statistically significant for both diseases (Figures 2 and 3). The QoI fungicides were not effective, however, the fungicides with new chemistries and with multiple mode of actions showed better performance than QoI fungicides alone for disease management and yield response.

2018 fungicide on frogeye
Figure 2. Frogeye leaf spot severity in upper soybean canopy in fungicide treatments combined across all seven experiment locations in 2018. Means followed by the same letter are not statistically significant from one another.

 

2018 fungicide on brown spot
Figure 3. Septoria brown spot disease index (%), which is a combination of how high the disease was observed in the plant canopy and disease severity at the maximum height of disease, for fungicide treatments combined across all seven experiment locations in 2018. Means followed by the same letter are not statistically significant from one another.

Management recommendations

Fungicides with solo QoI active ingredients had limited efficacy against frogeye leaf spot and provided less yield benefit compared with fungicides with multiple chemistries, especially some of the newer chemistries. C. sojina strains resistant to QoI fungicides have been confirmed throughout Iowa. An integrated method of disease management that does not depend only on fungicides should be employed to maximize disease management to preserve efficacy of existing fungicides. Other disease management practices such as crop rotation, planting of disease-resistant cultivars, and application of fungicides with multiple modes of action should all be used as tools for effective soybean disease management.

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on February 11, 2019. The information contained within may not be the most current and accurate depending on when it is accessed.

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Daren Mueller Associate Professor

Dr. Daren Mueller is an associate professor and extension plant pathologist at Iowa State University. He is also the coordinator of the Iowa State University Integrated Pest Management (IPM) program. Dr. Mueller earned his bachelor's degree from the Univ...