Snow Mold of Cereals

Pathogen Facts

  • The term “snow mold” is a blanket term for any of the several fungal diseases that develop on cereal crops underneath snow..
  • The most common snow molds are pink snow mold, Typhula rot (called gray or speckled snow mold), and Sclerotinia snow mold.
  • This disease only occurs in areas that receive dense layers of snow prior to soil freezing.

Photo - Snow mold symptoms in a field trial.

Snow mold symptoms in a field trial. Photo courtesy of Sam Tragesser, Senior Research Associate.

Conditions Favoring Disease

  • These fungi perform best at 68° F (20° C) but they can infect plants at temperatures as low as 32° F (0° C).
  • Snow on top of unfrozen soil provides cold, dark, and humid conditions that are favorable for these microorganisms.
  • Areas of the field with thicker layers of snow cover are more conducive for infection and will typically show more severe symptoms.
  • Early-planted wheat is more likely to become infected due to lush growth which can aid in the transmission of the fungi from plant to plant.
  • Once temperatures warm and fields dry out in the spring, disease development will halt.

Identification

Pink Snow Mold

  • Caused by the fungal pathogen Microdochium nivale (Fusarium nivale).
  • Pink coloration develops on the leaf surfaces from masses of conidia (asexual spores).
  • Mild winters with more moisture are more favorable for this snow mold.

Gray/Speckled Snow Mold

  • Caused by the fungus Typhula incarnata and Typhula ishikariensis.
  • White to gray mycelial mat with dark colored sclerotia give the characteristic “speckled” appearance on infected tissue.
    • Speckles can range from darker colors to reddish spots.
  • Needs 100 days of continuous snow cover paired with unfrozen ground.

Sclerotinia Snow Mold

  • Caused by the pathogen Sclerotinia borealis.
  • Very similar in appearance to speckled snow mold but overwintering structures are larger and darker sclerotia.

Management Considerations

  • Selecting resistant cultivars and varieties can lessen the severity of infection.
    • No variety is completely resistant.
  • Crop rotations away from winter cereals can reduce the build up of inoculum in the growing system.
  • No-till seeding has proven to be effective at mitigating the severity of disease.

References



Author: Madeline Henrickson

The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary..

May 2020