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    • Soy Uses
    • Market Development
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What Fungicide or Product Should I use to Manage White Mold and how Should I Apply it?

6/21/2022

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PictureFigure: White mold fungicide efficacy trial conducted in 2020. Red bars are yield and blue bars are white mold disease severity index.
Each year we conduct white mold fungicide efficacy trials. We examine old and new fungicide products, fungicide timing and application techniques. The two following graphs are snapshots from individual trials conducted over the last two years at the MSU Montcalm research station. We conducted these trials in 15” rows at a population of approximately 160,000 plants per acre, in irrigated fields with a history of white mold. The soybean variety used was moderately susceptible to white mold.

Note, the amount of white mold that developed in the trial is expressed as the disease severity index (disease severity x disease incidence) and is shown in blue, while the respective yield (bu/A) of each treatment is shown in red. Disease severity index or yield that is different between treatments is indicated with different letters. Also take note of the different application timings that are indicated such as R1 (beginning of flowering – plants have at least one flower on any node), R2 (full flowering - there is an open flower at one of the two uppermost nodes), and R3 (beginning pod - pods are 3/16 inch at one of the four uppermost nodes).

In addition to conducting these trials, we also collaborate with colleagues in states across the north central region allowing us to collect data on product performance over multiple environments. The fungicide efficacy table is a consensus of product performance for white mold and other soybean diseases and can be found here:
https://cropprotectionnetwork.org/publications/fungicide-efficacy-for-control-of-soybean-foliar-diseases
​

In addition to making the decision of what to apply, the “how” of fungicide application is also very important. For ground rig applications the following considerations should be made
  • Apply 15 to 20 gallons of water per acre 
  • Adjust nozzle pressure to around 40 psi 
  • Maintain ground speed at 10 mph or less 
  • Utilize nozzles that produce a single flat fan spray pattern directed straight down into the canopy
  • Select nozzles that generate fine to medium droplets
  • Use the mid-point in the crop canopy as your target and adjust the boom height from this point
 
A helpful article discussing these points in more detail can be found here: https://www.canr.msu.edu/news/equipping_and_operating_sprayers_to_control_insects_and_diseases_in_soybean


Picture
Figure: White mold fungicide efficacy trial conducted in 2021. Red bars are yield and blue bars are white mold disease severity index.
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Should I Spray for White Mold, and if so, When?

6/13/2022

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​Foliar fungicide applications can be an effective and profitable white mold management tactic provided the following conditions are met:
  • Fields have a history of white mold 
  • Current and future weather conditions favor white mold development (air temps below 85 degrees Fahrenheit and rainy or overcast)
  • Fungicide of choice has a proven performance on white mold 
  • Fungicides are applied at the optimum time for white mold suppression
 
As the white mold fungus infects through flowers or fallen flower petals, fungicides for soybean white mold management should be applied at or between the R1 (beginning flowering) and R3 (one pod 3/16” long on the upper four nodes having a fully expanded leaf on the main stem) growth stages. However, we have noted that in some years later or earlier applications within this window favor disease management. The variation in responses to fungicide timing from year to year is driven by the timing of apothecia development. 

Is it possible to scout for apothecia? Not really. Apothecia are small in size (up to ¼ inch) and you don’t need many of them to generate spores to infect plants. Apothecia are also often confused with mushrooms of other fungi such as the birds nest fungus, see figures.
 
To address this variable fungicide timing response and the difficulty in scouting for apothecia, “Sporecaster” was developed. Sporecaster is designed to predict the probability of apothecial presence. However, fields still need to be scouted to determine if the soybean crop meets thresholds such as canopy closure and reproductive stages. 
To use the “Sporecaster” app download it onto your phone from the Apple Store or Google Play. The app allows users to locate and setup multiple fields and run the apothecial risk prediction model using weather data from a third-party provider (Dark Sky API). 

Once Sporecaster is opened you can create multiple fields to determine their apothecial risk. The app will prompt the user for information, such as field name, row spacing, if the field is irrigated and the field location. Then the risk of apothecial presence can be calculated. The model will only run if it is told that flowers are present and if canopy closure meets threshold (for 30” row spacing only). A forecast risk expressed in percentage units is then shown, with red being above the 40% action threshold for a fungicide application. It is possible to rerun the model as desired and even go back to previous years to examine previous risk.
 
What about spraying for other soybean foliar diseases? In general, we don’t see a great deal of other foliar soybean diseases in Michigan. However, southern Michigan may warrant a fungicide application for frogeye leaf spot. Under heavy frogeye leaf spot conditions, we have seen a 20 bu/A protection over an untreated when sprayed at R3. However, this was a field that we had purposefully infected with frogeye and were irrigating to promote disease. Occasionally we will also see Septoria brown spot moving up the canopy. A fungicide application tends to be warranted when Septoria infected leaves are found halfway up the canopy. Most often when not treating for a specific disease, fungicide applications result in a breakeven proposition, however there is variability in response from field to field. If you make the decision to spray, check strips should be included to learn and verify the decision. 
Picture
Figure: White mold apothecia and sclerotia on soil surface (Jill Check)
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Figure: Very common "bird's nest" fungus, a harmless fungus often confused with white mold apothecia.
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Figure: Screen capture from Sporecaster, a phone App for predicting the risk for white mold apothecia (mushrooms) to develop, showing low (blue) medium (yellow) to high (red) risk depending on the location and other field-specific information.
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Will White Mold be a Problem in 2022?

6/6/2022

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​Martin Chilvers, Associate Professor and Field Crop Pathology Specialist, Jill Check, PhD candidate, Austin McCoy, postdoctoral associate, Mike Staton, MSUE soybean educator
PictureFigure: Correlation of soybean variety yield (bu/A) against white mold disease severity index. Note the differences by variety (orange dots), with a decrease in yield as white mold disease severity increases.
The answer to this question will depend upon three factors that must come together, the prevailing weather, presence of the white mold fungus and susceptibility of the soybean variety. 
​
White mold of soybean is an annual problem for some producers and can be particularly severe when conditions are cool and wet during flowering. This disease is often most problematic in soybean fields having productive soils, planted at a high population with narrow row spacing (<30 inches). Canopy closure provides a humid, shaded environment that is conducive to white mold apothecia (mushroom) formation and plant infection, especially in cool, wet years. No soybean variety is completely resistant to this disease, however, as shown in the figure below, even within a company there are varieties which are far more tolerant and perform better under white mold disease pressure. Selecting a variety that is tolerant to white mold, as well as planting lower soybean populations and utilizing wider row spacing can help manage the severity of this disease. Company catalogues do provide white mold ratings, but it is always wise to check with your seed dealer, especially if you have had issues managing white mold in the past. Knowing variety susceptibility can also help inform in-season management decisions such as fungicide applications.

​​The weather that we receive shortly before and into July will heavily dictate the degree of white mold disease that develops later in the season. A cool (<85o F), wet July means favorable conditions for the white mold fungus to produce apothecia (mushrooms) that release spores and infect the plant primarily through the flowers or fallen flower petals. Disease won’t be readily apparent until August when cottony mycelia of the white mold fungus start to be produced from infected plants and plants begin to wilt. In addition, producers that irrigate will be at increased risk of white mold and should consider less frequent but heavier waterings. Irrigators should also hold off watering as much as possible until the R3 growth stage (one pod 3/16” long on the upper four nodes of the main stem having a fully developed leaf node).

PictureFigure: Nearly constant precipitation during the month of July in 2014 coupled with much below average temperatures resulted in a devastating white mold epidemic, particularly in the thumb area of Michigan.
​Finally, the third in the trifecta of white mold disease development is the presence of the white mold fungus. Unfortunately, the white mold fungus can survive for many years in the soil as sclerotia. Seed lots can also be infected or infested with the white mold fungus and can act as another source of inoculum. White mold inoculum typically does not move very far from the source. However, in the white mold epidemic of 2014 it did appear that the excessively foggy, wet, and cool July may have seen dispersal of white mold spores into fields with no previous inoculum source. Tillage can also play an important role in inoculum movement and survival. Tilling fields will bury the sclerotia resting bodies where they are more likely to survive and then germinate once brought to within the top inch or two of the soil profile. Sclerotia buried deeper are unlikely to be able to produce an apothecia (mushroom) on the soil surface. Under no-till systems there is evidence that sclerotia do not survive as well on the soil surface.

Picture
Figure: Sclerotia of the white mold fungus (Sclerotinia sclerotiorum) and resulting apothecia (mushroom) that will release spores
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