Disease Management: Webinar: Managing Soybean Diseases

Stephanie Porter, Soy CCA Envoy from West Central Illinois and Sales Agronomist with Burrus^® Hybrids, reviews the most prevalent soybean diseases, all of which have the potential to lower yields. She explains the set of conditions needed for each disease to infect soybean plants, ways to prevent the disease, and how to manage it if it’s present in growers’ fields.

Key Takeaways:

• The disease triangle consists of the environment, host and pathogen
• Growers should choose a variety that will protect against diseases that they typically see out on their acres
• Crop rotation is a good practice to adopt, but it doesn’t help prevent all disease
  • Charcoal rot can infect other crops, like corn
• Many diseases are easily confused with others, so it’s important to carefully identify which disease it is
  • Growers can also send samples to a plant clinic for definite identification
• Some diseases (Frogeye leaf spot, Septoria brown spot, Cercospora leaf blight) will respond to fungicides, but bacterial diseases and downy mildew will not

Question and Answer

• Is there true genetic resistance to seedling disease or is it mainly vigor and tolerance?
  The answer is all of the above. It is very likely that soybean varieties differ in their susceptibility to various root rot pathogens. However, the seed quality and genetics, as well as environment conditions (crop rotation, soil conditions, weather, tillage) in which the varieties are planted will also factor into the equation.

• How many fungicide active ingredients do we need in seed treatment today?
  In the case of the Burrus soybean lineup, we are very happy with the performance of our fungicide components, EverGol Energy™ and Allegiance^® within our standard seed treatment. When combined, they consist of 3 active ingredients. Two of these active ingredients provide control of fungal species such as: Fusarium, Rhizoctonia, Botryti cinerea, Phomopsis, Ascochyta. There is a “double shot” of another active ingredient (in both EverGol Energy™ and Allegiance^®) that will control oomycete species such as: Phytophthora, pythium and downy mildew. Therefore, the rate of the fungicide component in your seed treatment also can make a difference in the control of root rot pathogens. Seed treatment active ingredients for the control of SCN or SDS should be optional and based on your need.
• Is tiling a good disease management strategy in Illinois and should we put in more tile?
  YES and YES! Tiling is one of the best investments you can make on your farm and can be part of your integrated pest management strategy for disease control.
• How many races of Phytophthora are there?
  According to the following APS website “There are 55 coded races, but many more virulence combinations have been described in the US. Many publications today refer to the pathotype, the exact listing of virulence reactions that each isolate has on the isolines of the differential set rather than a race code number, as the number of races and diversity has become too great.” To learn more click here.
• What the top three soybean diseases in Illinois (not including SCN)?
  1.) Sudden Death Syndrome 2.) white mold 3.) Pythium. This answer will depend on environment, soybean variety resistance, and management.
• How common is Northern Stem Canker Complex and is that mainly a bacteria disease since fungicides don’t work?
  I am not sure of the incidence of Northern stem canker in Illinois, but I do know it is an upcoming disease that you should look out for if environmental conditions are conducive (early cool, wet weather or high fertility), paired with management methods such as no-till, high populations, and susceptible soybean variety, or rotation with alfalfa.
  Northern stem canker is a fungal disease. Once a fungal pathogen such as (SDS, Brown stem rot, stem canker, white mold) infects or blocks the vascular system of a soybean stem, there is no in-season fungicide rescue treatment.
• You never talked about Brown Spot but is it very common?
  I did mention it, but it may have been confusing because it is also called Septoria leaf blight or Septoria brown spot. Yes, it is very common and will infect during warm, wet conditions starting with lower leaves and then work its way up. There may be differences in soybean variety susceptibility and fungicides may be warranted if most of the field has more than 1/3 of the canopy infected at the R3 growth stage.
• What is it about hot and dry weather after mid-summer that causes some diseases to flourish?
  In my opinion, any fungal pathogen or pest such as SCN that compromises root mass or blocks water flow to the plant will only cause the plant to suffer more during mid-summer hot and dry conditions. Thus symptoms become more evident.
• Can some of these soybean diseases overwinter on corn residue?
  Yes, as far as I know the pathogen that causes SDS can overwinter on corn residue. There is also research being conducted to evaluate cover crops for fungal pathogen survival.
• How early in the summer can we actually see foliar SDS symptoms?
  Most of the time SDS symptoms do not show up until the reproductive stages of soybean. The earlier that they show up will equate to more yield loss due to earlier loss of foliage.
• What diseases are ‘hot’ in Southern Illinois?
  When in southern Illinois, you are more likely to experience warmer temperatures than the rest of the state. This means that you could be the first to find foliar fungal diseases such as frogeye leafspot, Septoria brown spot, and Cercospora leaf blight. Pay attention to soybean variety ratings for Frogeye, or scout to see if a fungicide application is warranted at R3 for all these fungal foliar diseases. Southern Illinois will also be the first to see soybean rust that blows up from the South, but it has not been a major threat in previous years.
• How long will SDS organism survive in the soil?
  Most sources say “several years”.
• Is R3 the best ‘catchall’ time to apply a fungicide?
  Yes, because we are wanting to protect leaves during grainfill. The exception to this rule is white mold, because we need to apply a fungicide before infection at late bloom.
• What is the best strategy today for managing frogeye since resistance exists?
  Remember that fungicides are not the only answer to disease control. We need to use an integrated pest management approach and use other management tactics such as crop rotation and plant varieties that have good disease ratings. Also, you can scout and only apply fungicides if diseases are present. You cannot rely on one class of fungicide; therefore, pay attention to what you are applying and rotate fungicide groups. Do not apply the same group of fungicide repeatedly in the same year. If all of these steps are followed, we can keep selection pressure for resistance down and preserve effectiveness as well as longevity of a fungicide. Click here for more information.

1 CEU in Pest Management is available for this webinar. Visit the Certified Crop Adviser website to self-report your credit after viewing the webinar recording.