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:
- 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.
- 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.
- 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.
- 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.
- If there was a second, smaller ear on a plant infection levels seemed to be much worse.