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    Arkansas Soybeans: Understanding Yield Impacts of Septoria Brown Spot

    Septoria brown spot is a foliar disease caused by the fungus Septoria glycines. Most people scouting soybean in Arkansas have noticed this disease beginning in the lower canopy. It is likely detected before other foliar diseases develop.

    Septoria brown spot is often the first one we see. In the lower canopy, it impacts leaflets that do not contribute to pod formation and fill during the later reproductive stages of soybean development and therefore does not impact yield.

    However, like many other foliar diseases, if brown spot occurs in the upper third of the canopy, it can damage green tissue that would otherwise be making energy for pod fill before R6 (Figure 1). In this case, our data shows that significant yield losses can occur.  

    Soybean plants with severe Septoria brown spot infection. Leaves are yellowed with brown spots, some having holes. Research in Arkansas, County, 2021

    Figure 1.  Severe Septoria brown spot occurring in the nontreated control in an on-farm trial in Arkansas County, 2021. Click Image to Enlarge

    Effective Recommendations for Severe Septoria brown spot

    Generally, the recommendation for in-season management of foliar diseases that occur on soybean would be to scout. If the disease is spreading due to favorable weather conditions, apply a foliar fungicide to protect tissue not yet impacted. Products containing multiple modes of action have been effective in yield protection in our trials where Septoria brown spot was severe (Tables 1 & 2).

    Table 1.  Results of an on-farm foliar fungicide trial in Lonoke County in 2020.

    Fungicides Applied Septoria Brown Spot Incidence (%) Septoria Brown Spot Severity (%) Yield Bu/A
    Miravis Top 13.7 Fl Oz/A 7.29 a 2.54 a 37.4 b
    Nontreated 85.41 c 70.83 c 28.5 a
    Revytek 8 Fl Oz/A 27.08 b 15.04 b 37.3 b

    Means with the same letter are not significantly different using Tukey’s honest significant difference test at P = 0.05.

    Table 2.  Results of an on-farm foliar fungicide trial in Arkansas County in 2021.

    Fungicides Applied Septoria Brown Spot Severity

    (0-9)

    Aerial Blight

    (Per 5 Meters)

    Yield

    Bu/A

    Miravis 13.7 Oz/A 2.1 a 3.2 b 78.4 c
    Nontreated 6.2 c 3.1 b 72.4 a
    Revytek 7 Oz/A 3.4 b 0.8 a 76.2 b

    Means with the same letter are not significantly different using Tukey’s honest significant difference test at P = 0.05.

    Weather Patterns and Septoria brown spot

    We would also expect much of the damage that we see from foliar diseases in our state to occur on later planted or later maturing soybean when the temperatures have cooled slightly, and rainfall is becoming more frequent. However, in on-farm trials in 2020 and 2021, fields where yield losses occurred due to Septoria have been R3 in late June.

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    These trials were all 25-50 acres with fungicide treatments replicated three times and a nontreated control block included in each replication.

    Weather data collected from on-farm trial locations between R3 and R6 indicated that when compared to fields where Septoria did not occur or was not yield-limiting, the average rainfall was less, but the humidity was around 2 percentage points higher.

    Temperatures among these locations were similar (Table 3). Based on my observations and conversations with others, I don’t think it’s coincidental that we are currently seeing Septoria brown spot advancing up the canopy in many fields while experiencing high heat and humidity around the state.

    Table 3.  Weather data compiled from 8 locations in 2020 and 2021 where Septoria brown spot occurred and was severe or not.

    Severe Septoria Brown Spot Average Maximum Humidity (%) Average Minimum Humidity (%) Average Humidity (%) Average Maximum Temperature (°F) Average Minimum Temperature (°F) Average Temperature (°F) Average Rainfall (In)
    NO 90.6 52.4 73.9 90.9 73.7 81.6 0.16
    YES 92.9 55.4 75.4 90.4 72.8 81.0 0.11

    Practices to Consider

    If Septoria brown spot does occur in fields this season and is severe, take action to limit its impact next season and into the future. Since we do not have a comprehensive list of varieties that are more or less susceptible to Septoria, choosing less susceptible varieties may be difficult.

    Because the Septoria glycines fungus overwinters on soybean debris, tillage and rotation to another crop, at least for one season, are good practices to consider. Some evidence suggests Septoria brown spot is more severe in fields grown in continuous soybean every year.

    As always, should you need assistance, do not hesitate to reach out to me or Travis Faske.

    Contact Email Phone
    Terry Spurlock tspurlock@uada.edu (501) 676-3124
    Travis Faske tfaske@uada.edu (501) 676-3124

    Acknowledgements

    We thank the Arkansas Soybean Promotion Board for funding the research discussed in the blog article as well as the cooperating farmers, consultants, and county agents that helped coordinate the on-farm fungicide trials mentioned here.




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