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Move over Mold: How to manage White Mold beyond 2017

  • Oct 19
    Maizex Market Development Agronomist - Leigh Hudson
    Move over Mold: How to manage White Mold beyond 2017 By Leigh Hudson on October 19, 2017
    Categories: Disease Control, Soybean

    2017 is a year for the books, and for most, it is a chapter to be forgotten.  With this wet, cold weather, Mother Nature provided a paramount environment for our beloved soybean disease: white mold.   Across Ontario and Quebec, white mold is present in almost every soybean field.  Some worse than others, but for the most part, it is there. Now what? How do we manage this going forward?

    White mold infection and development is favoured by rain, cool temperatures, high humidity levels and moist soils that are contained by the soybean canopy.  Once the fungus is established, it can survive for 8 years or more as sclerotia (see Figure 1,2,3) in the soil.  The apothecia; beige mushroom like growths, that grow from the sclerotia at the soil surface (Figure 4), produce the fungal spores. These spores cause growth of the white fuzz infection, mycelium (Figure 5) in season by entering at the nodes via flowers during the reproductive stages. The infection then causes premature death and inadequate pod fill, resulting in yield loss.


    Figure 1. Sclerotia inside a soybean stem (Source: Crop Protection Network)

     

    There are multiple things that can be done to manage your white mold pressure after a year like 2017. This can be done through various cultural practices such as crop rotation, variety selection, reduced tillage, stand population, fertility management, weed control, and fungicide application.

    Crop rotation with 2-3 years of alternative host crops (ie. corn, wheat) is an excellent way to decrease your white mold pressure. Also avoiding high risk situations such as soy-soy rotations and/or inclusion of other white mold susceptible crops (ie. canola, edible beans).

    Selecting varieties with excellent yield potential in combination with excellent white mold tolerance is desirable.  Varieties with upright plant stature is also ideal, allowing air movement throughout the canopy.  Varieties with good standability is also an asset, for lodging provides an environment with higher risk for white mold.


    Figure 2. Sclerotia on the outside of the stem (Source: OMAFRA)

     

    Reduced tillage can have a significant effect on sclerotia survival, especially when paired with an adequent crop rotation.  Sclerotia are most viable when buried 8” or more.  Increased tillage results in early canopy development, providing a favourable environment during early flowering stages (R1-R3).

    Reducing plant stand population will help with stand density and increased air movement.  Pairing this with wider row widths will also increase your air movement through the canopy. Planted with a drill or planter, populations as low as 120,000 plants/ac can be sufficient to maximize yield potential while in turn reducing your white mold risk (Source: Purdue University).


    Figure 3. Sclerotia in soybean sample after harvesting. (Source: Prairie Stock Photo)

     

    High soil fertility can create a high risk environment, resulting in extensive plant growth, creating a dense, lush canopy. For example, if a spring application of manure occurs, the available nitrogen in the manure causes the soybean plant to put a lot of that nutrient into foliage production, resulting in a thick, rich stand.  Scenarios like this can also cause plants to grow taller than average, increasing risk of lodging.

    Weed control is important for various reasons, but in this case, good weed control will keep broadleaf weeds at bay and canopies free of plants that can reduce air movement through the stand. Some weeds also act as disease hosts: lambs quarters, ragweed, pigweed and velvetleaf (Source: Dupont). Some herbicides also supress sclerotia and disturb the fungal life cycle.


    Figure 4. Apothecia growing on soil surface. (Source: University of Delaware)

     

    Protecting the flowers with fungicides can be an effective way of reducing your white mold infection.  If conditions are right for the apothecia to release spores into the stand,infection will occur.  The application timing of fungicides is critical for optimal protection, being R1-R3. In many situations, 2 applications might be necessary to give maximum flower coverage.


    Figure 5. White Mycelium growth. Symptom of white mold on the outside of the plant. (Source: Leigh Hudson)

     

    Leigh Hudson CCA-ON, Market Development Agronomist, Eastern Ontario, Maizex Seeds

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