There was a lot of white mould in the Ontario soybean crop in 2014. Conditions that favour white mould growth and what can be done to reduce it is summarized below.

Factors favoring white mould

  1. High yield potential crop/field
  2. Field history of white mould
  3. Susceptible variety
  4. Short soybean rotation
  5. Dense canopy — High plant population, narrow rows and early planting
  6. Poor weed control (hosts)
  7. In-season weather conditions — cool and moist are favourable for white mould

IPM for white mould management

  • Keep good field records of disease level
  • Variety Selection
    1. Best available level of tolerance
    2. Appropriate maturity
    3. Upright, non-bushy with good lodging tolerance
  • Cultural practices such as:
    1. Reduce plant populations and increase row width
    2. Rotate with non-host crops (2 to 3 years non-host such as corn and wheat)
    3. Reduce tillage but avoid soybeans on soybeans - high risk situation
  • Fungicides — target fields at risk (above)
    1. Many chemical/biological options
    2. Proper timing and coverage critical —
      • First spray at R1 (first flower) with 2nd application at R3 (pod forming) if necessary
A soybean field in August showing significant white mould damage.
Figure 1. White mould — a soybean field in August showing significant white mould damage.
Apothecia Sclerotia in the soil will produce mushroom-like structures called apothecia that eject spores onto the soybean plant.
Figure 2. Apothecia Sclerotia in the soil will produce mushroom-like structures called apothecia that eject spores onto the soybean plant.
Sclerotia stem after the spores inoculate the plant, the fungal pathogen grows and consumes plant nutrients which cause the stems to girdle, this kills any plant tissue above and results in injury as shown in Figure 1.
Figure 3. Sclerotia stem after the spores inoculate the plant, the fungal pathogen grows and consumes plant nutrients which cause the stems to girdle, this kills any plant tissue above and results in injury as shown in Figure 1.
Selerotia pod the black sclerotia, as seen here attached to a soybean seed within the pod, which when re-introduced to the soil will start its life cycle all over again.
Figure 4. Selerotia pod the black sclerotia, as seen here attached to a soybean seed within the pod, which when re-introduced to the soil will start its life cycle all over again.