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Gibberella ear rot (Fusarium graminearum / Gibberella zeae)

pinkish mould beginning at cob tip

Gibberella ear rot: biology

Gibberella ear rot is the most common ear mould in Ontario. The fungus overwinters on crop residue, and the inoculum that causes Gibberella ear rot is present every year.

As with any disease, the pathogen (Fusarium graminearum) needs a susceptible host (corn) and the right environmental conditions at the right time (silking) to initiate infection. Primary infection takes place through the silk channels when warm, wet or humid weather occurs at silking. Corn is most susceptible to infection when weather conditions are cool and wet two to 10 days after silk initiation.

If weather conditions at silking are conducive to infection, environmental conditions during grain fill determine the severity of infection. Warm temperatures coupled with high humidity, heavy dew or frequent rains and increased cloud cover are ideal for ear mould to thrive.

Secondary infection can occur through damage to cobs (ie. insect feeding, bird feeding, hail, mechanical damage) when a pathway is created for the pathogen to enter.

Gibberella ear rot: Damage description

Gibberella ear rot is characterized by pinkish-orange or white mould; infection begins at the cob tip and, in severe cases, moves down towards the base. Generally, reddish mycelium will colonize only part of the ear, but in severe cases, the ear husk and cob can fuse together.

Sometimes the fungus can appear as a white-coloured mould, which makes it difficult to distinguish from Fusarium ear rot. This pathogen can produce many toxins, including deoxynivalenol (vomitoxin or DON), zearalenone (ZEN) and T-2 toxin. If grain is to be used for feed, test mycotoxin levels.

Looking back at 2018, many areas in Ontario experienced a tough early season and drought stress prior to tassel. Any stress on plants left them more vulnerable to disease. Here are some other significant factors that contributed to high DON levels in many crops in 2018:

  1. Several fields emerged unevenly, largely due to tough planting conditions. Uneven emergence can cause uneven silk emergence from plant to plant. Cobs from later emerged plants tend to have smaller ears. The smaller ears would have a tighter husk.
  2. Drought stress at silking can slow silk emergence or cause uneven silk emergence, lengthening the time during which the cob is exposed to the Gibberella inoculum.
  3. Anything that prevents cobs from filling to the tip will cause husks to close more tightly. Husks that closed more tightly were more prone to higher infection. This can be influenced by hybrid characteristics or factors such as drought stress, low fertility, or compaction.
  4. Upright ears showed more visible ear mould than ears that hung down, which allowed moisture to escape the cob. Upright ears can be a hybrid characteristic.
  5. If there was a second, smaller ear on a plant infection levels seemed to be much worse.

Gibberella ear rot: Management

Management practices to reduce your risk this season:

  1. Crop rotation. Infection in corn on corn acres will be worse. If planting corn on corn, rotate hybrids.
  2. Hybrid selection is a key management factor. There are differences in hybrid susceptibility; plant multiple hybrids to spread risk. While there are some hybrids that are consistently better or consistently worse than others, every year is different. Some hybrids with a historically good track record for ear mould showed high susceptibility in 2018. Planting date and flowering date impacted the level of susceptibility for some hybrids in some fields.
  3. Uniform emergence is critical. Perform proper planter maintenance and replace worn parts. Create a uniform seed bed, avoid planting into wet soil conditions, and ensure uniform planting depth.
  4. Plant at optimal populations. Higher plant density can increase risk.
  5. Control insects such as western bean cutworm and earworm. These insects create pathways for secondary infection of ear mould. Hybrids with the Agrisure Viptera® trait are extremely effective at controlling these insects. Voliam Xpress® insecticide has fast knockdown and residual control for hybrids without the Agrisure Viptera® trait.
  6. Use a fungicide with ear mould suppression on the label at R1 if ear mould management is your primary concern. If leaf diseases such as northern corn leaf blight are your main concern, then fungicides such as Trivapro™ still do a great job protecting the yield potential of your crop.
Scout for ear rot from R5- R6 (dent to black layer/maturity). Harvest early if more than 10% of plants display ear rot. Dry and cool harvested corn quickly and test grain for mycotoxins before feeding it to livestock.

The best timing for Fusarium management with fungicides is at R1 (silk emergence):
  • R1 is the first stage of the reproductive phase
  • Silks remain receptive to pollen for up to 10 days after silk emergence
  • The window of application to optimize fungicide performance is about 7 days starting at R1
Once the crop reaches R2, the optimal application window has closed.

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