Early season diseases in soybeans

Now that the soils are warming, some producers are discussing planting soybeans in the ground.  When considering early planting of soybeans, there are two diseases that should be considered: 1) Sudden death syndrome (SDS)  and 2) Pythium root rot (PRR)

Both SDS and PRR are favored by cool, wet weather.  In the case of SDS, early season infections can reduce stands, and also result in colonization of root systems.  The SDS pathogen remains in the lower portion of the stem and roots until the the plant reaches the reproductive stages.  Heavy, alternating rains during reproduction can cause the fungus to more aggressively colonize the plants, as well as produce toxins, which can cause defoliation, wilting, and reduced yields.  If considering early planting into fields with a history of SDS, ensure that you select a cultivar with excellent SDS resistance and consider an SDS-seed treatment if it fits your production practices.

PRR is actually a complex of Pythium species that each have their own unique characteristics.  It is now understood that individual Pythium species and even isolates within species can differ significantly in their optimal temperature for infecting seedlings.  Regardless of temperature, if the growth of your soybeans is reduced due soil water saturation or cool conditions, you may see increased stand issues.  There are specific seed treatments that can be effective for suppressing Pythium.  However, it is important to realize that these treatments provide a window of protection that is intended to protect the emerging seedling and allow it to establish.  This window typically is 2-3 weeks.  Seed treatments will not protect a submerged seed from dying due to flooding, and will not provide protection after than window of protection is reached.  Remember- seed treatments are not fumigants- they are short-term, protective barriers.  Tile can be a great investment in fields prone to flooding and subsequent PRR issues.


Soybean Quality Issues in 2019

I have had several conversations with members of the agricultural community regarding seed quality resulting from issues derived from delayed harvest and persistent wet conditions encountered in many parts of Illinois in 2018.  For more information on what seed producers and soybean farmers should keep in mind going into this season, see my new article published on the Illinois Field Crop Disease blog, found by clicking here.


Dectes Stem Borer and Lodged Soybeans

Many soybean growers have had problems with lodging at harvest this year. The primary culprit for this (as for many of our woes this fall) was the extended period of unfavorable weather that we have suffered. However, in parts of southern Illinois damage by the dectes stem borer contributed to this problem.

The adult dectes stem borer (Figure 1) is a “long-horned” beetle that can often be found in soybean and on other plants. The adult female chews a hole into the surface of the plant (usually at the petiole), and lays her eggs in the pith. This often results in individual petioles wilting or falling completely off of the plant, which is usually the first sign of an infestation. Upon hatching, the larva (Figure 2) tunnels throughout the stem and feeds on the pith. As the plant nears maturity, the larva moves into the base of the stem where it will spend the winter. As awful as the bored-out stem of a soybean plant looks after being attacked by dectes stem borer (Figure 3), economic losses only occur if this damage leads to lodging. When preparing to overwinter, larvae will often girdle the base of the stem, causing the plant to break off and leading to harvest difficulties and reduced yield (Figure 4). This insect has one generation per year, with the adults usually emerging from soybean residue beginning in late June in Illinois to start the cycle again.

Adult dectes stem borer

Figure 1. An adult dectes stem borer at rest.

 

Larva of the dectes stem borer

Figure 2. A larva of the dectes stem borer removed from a soybean stem

Dectes stem borer larva in soybean stem

Figure 3. Damage to the inside of a soybean stem caused by a dectes stem borer larva

Soybean lodging caused by dectes stem borer

Figure 4. Lodged soybeans due to dectes stem borer feeding (Photo: Eric Alinger, Dupont Pioneer)

Insecticides are generally not recommended for control because the larvae are protected within the stem and the adults lay eggs over a long period of time in the summer (approximately mid-July through August in Illinois). While there appear to be some differences in varietal susceptibility, these differences are not well documented, and to my knowledge no soybean varieties have been characterized as resistant to dectes stem borer. However, there are some cultural management options available to producers:

  • Monitoring. While there is no economic threshold established, finding adults at higher than average numbers will be the first indication of a problem. Note wilting or broken-off petioles, and split soybean stems toward the end of the season to gauge the level of infestation. In addition, examine soybean stems in lodged areas to determine if dectes stem borer was part of the problem. If you have never done so before and you are in southern Illinois, the results might surprise you.
  • Timely harvest. Obviously, we would harvest on time every year in every field if we could. However, if you note fields that are infested with dectes stem borer, put those fields as early as possible on the priority list to reduce the potential for lodging.
  • Soybean stubble. Destroying or burying soybean stubble in the fall reduces dectes numbers locally, but the adults readily move from their overwintering sites to surrounding fields. Areas with a lot of no-till production are likely to have more issues with dectes stem borer.
  • Alternate hosts. Dectes stem borers feed on several other host plants, including sunflowers and giant ragweed. Areas with high populations of these plants could have higher populations of dectes stem borers as well. (As if you needed another reason to kill giant ragweed).

Contact:

Nick Seiter nseiter@illinois.edu (217) 300-7199

Research Assistant Professor, Field Crop Entomology

University of Illinois Department of Crop Sciences


Soybean Gall Midge: New Pest of Soybean in Nearby States

Producers in Nebraska, Iowa, and South Dakota have been dealing with gall midges in soybean. This is a fly in the family Cecidomyiidae, which is the same family as the Hessian fly, sorghum midge, and several other agricultural pests. We have not confirmed any infestations of this insect in Illinois at this time; the closest confirmed, damaging infestations that I know of are in western Iowa. However, because so little is known about the biology of this insect, producers should learn to identify it in case it does show up in Illinois. The following links to material produced by my colleagues in Iowa and Nebraska contain information on the identification and distribution of this insect pest; if you find any potential infestations within Illinois, please let me know at the contact information below. Happy scouting!

https://crops.extension.iastate.edu/cropnews/2018/07/new-soybean-pest-iowa-soybean-gall-midge

https://cropwatch.unl.edu/2018/orange-gall-midge-soybeans

 

Author:

Nick Seiter nseiter@illinois.edu (217) 300-7199

Research Assistant Professor, Field Crop Entomology


Spray Decisions for Frogeye Leaf Spot on Soybeans

Many people have asked about the need to make a fungicide application for frogeye leaf spot on soybeans this season.  I have posted a new article on the Illinois Field Crop Disease Blog which reviews this pathogen, how it works, and some new tools that may help you with these important decisions.  Find the article by clicking here.


Seedling Diseases in Soybeans – Time to Scout!

Now is the time that seedling diseases of soybeans will start to be apparent.  Indeed, we have started to see more images of soybeans that may have symptoms of seedling disease.  However, it is important to understand that seedling diseases are complex, and a simple picture often is not sufficient to adequately diagnose the issue.  I wrote a more extensive of seedling diseases of soybean on the Illinois Field Crop Disease Blog, which can be accessed here


Diagnosing disease related issues in the field

Well, it is that time of year where we start to see issues developing in the field.  Questions such as, “What happened?”  and  “Why me?” will become more common.  The key to managing diseases is proper diagnosis, and this starts in the field.  In my recent post on the Field Crop Disease Blog, I provide several tips for diagnosing issues in the field, and distinguishing disease related problems from abiotic issues.  Check out the post, and sign up for updates!


Slug Management in Illinois Field Crops

Authors: Nick Seiter, Talon Becker, and Nathan Johanning

Slugs can be a difficult pest to manage when conditions are favorable for them, which has been the case often (particularly in southern Illinois) over the last couple of years. These mollusks can damage both corn and soybean early in the season, along with a variety of other crops; however, they have the potential to be especially problematic in soybean, where they can kill the cotyledons and ultimately reduce stands. There are a few management points to consider for slugs in field crops:

  • Monitor slugs before planting to estimate the severity of the problem. Slugs can be monitored by inspecting residue, or by creating artificial shelters (made from shingles or other flat materials placed in the field to create a dark, damp environment) and inspecting them periodically before planting and during early stand establishment.1

    A slug found under a shingle trap placed in a field prior to planting in southern Illinois. Photo: Talon Becker.

  • Cool, wet weather during stand establishment results in greater slug problems. Slugs require a moist environment to survive, and they perform best when conditions are wet. Cooler temperatures extend soil drying time and delay plant development, leaving seedlings vulnerable to slug feeding damage for a longer period of time. Discussions with several CCAs in southern Illinois highlighted the fact that, while slug damage is a fairly normal occurrence on a small scale in most years, particularly in no-till fields, the mild winter of 2017 followed by wet and cool conditions in the spring after many acres had already been planted likely contributed to the greater incidence of slug damage last season. It appears that soybeans were most affected last season in southern Illinois, with several thousand acres of replanting reported.
  • Reduced tillage and/or certain cover crop systems can lead to larger slug populations. Higher levels of residue retain water and provide harborage for slugs, resulting in an increased probability of slugs reaching damaging levels. Reports from southern Illinois indicate that most problem fields last spring had a cereal rye cover crop that had not been terminated before producing excessive growth, creating a favorable environment for slugs. It is important to manage residue in cover cropped fields, particularly if they are no-till. If you had a problem with slugs last year, or have found concerning levels under your “shingle traps” in the field, make it a priority to terminate the cover crop before too much above ground biomass has accumulated (generally less than 1 ft. of growth). Cover croppers may also consider decreasing their seeding rate or planting a cover crop mix which includes species that winter-kill along with their favorite over-wintering species.
  • Avoid open seed furrows. When planter closing wheels fail to seal the furrow, the resulting trench provides an ideal environment for slugs and allows them to consume developing cotyledons as the seed germinates.
  • Chemical control options are limited. Slugs are not insects, and insecticides do not provide effective control. There are slug-specific baits available, but they tend to be expensive. Note that several formulations of the active ingredient metaldehyde (e.g., Deadline®) are labeled for use in corn, but this molluscicide is not currently labeled for soybean in Illinois.

Ultimately, the most reliable management tactic for slugs is to plant into a warm, dry seed bed, which is not always an option. However, by understanding conditions which are likely to lead to slug problems, you can be better prepared to address them when and where they occur.

Correspondence:

Nick Seiter: nseiter@illinois.edu – Research Assistant Professor, Field Crop Entomologist, University of Illinois Department of Crop Sciences

Talon Becker: tbecker2@illinois.edu – Extension Educator, Agriculture and Natural Resources, Illinois Extension

Nathan Johanning: njohann@illinois.edu – Extension Educator, Agriculture and Natural Resources, Illinois Extension

1 Douglas, M. R. and Tooker, J. F. 2012. Journal of Integrated Pest Management 3(1) DOI: http://dx.doi.org/10.1603/IPM11023