Gibberella Ear Rot
This is the most common and important ear mould. Infection often begins at the ear tip and moves down towards the ear base. In severe cases, the ear husk and cob fuse resulting in mummified ears. Although the fungus can produce a white-coloured mould which makes it difficult to tell apart from Fusarium Ear Rot, Gibberella produces a characteristic dark-red or pink coloured mould. Toxins produced by Gibberella include Deoxynivalenol (vomitoxin or DON), Zearalenone (ZEN) and T-2 toxin. If grain is to be used for feed, a mycotoxin test is recommended. (Figures 1 & 2)
Figure 1 - Gibberella ear mould
Figure 2 - Gibberella ear mould
Fusarium Ear and Kernal Rot
Unlike Gibberella, Fusarium infected kernels are often scattered around the cob or on kernels that have been damaged, for example by insects or bird feeding. Fusarium infection produces a white to pink or salmon-coloured mould. In most cases Fusarium does not fuse the husk to the ear. A "white streaking" or "star-bursting" can be seen on the infected kernel surface. Although many Fusarium species may be responsible for these symptoms, the primary species we are concerned about in Ontario is Fusarium verticillioides, which produces the toxin Fumonisin which is a human carcinogen. (Figure 3)
Figure 3 - Fusarium Ear Rot
Diplodia Ear Rot
The characteristic ear symptom of Stenocarpella maydis infection is a white mould that begins at the base of the ear and may eventually cover the entire ear. Mould growth can also occur on the outer husk, which has small black bumps (pycnidia) embedded in the mould. These reproductive structures are where new spores are produced. Unlike Gibberella and Fusarium, Diplodia does not produce any significant toxins. (Figure 4)
Figure 4 - Diplodia Ear Rot
Penicillium Ear Rot
Infection produces a light blue-green powdery mould which often grows on or between the kernel surface. However, it can led to internal discolouration of the embryo (Blue-eye mould). Infected kernels could become bleached or streaked. It can be a serious problem if corn is stored at high moisture levels (greater 18%). Ochratoxins are produced by many Penicillium species. (Figure 5)
Figure 5 - Gibberella, Penicillium/Trichoderma and Diplodia Ear Rot
Alternaria and Cladosporium
These produce a black mould on the ear and kernel surface. They are a problem when harvest conditions are delayed, injury from insects/birds occurs, or when premature crop death from frost occurs. Cladopsorium and Alternaria do not produce any known toxins. If properly stored or ensiled, mould growth stops under anaerobic (oxygen-free) conditions.
Small to almost non-detectable levels of mould in the field can lead to significant mould problems if they go undetected and are allowed to develop in storage. Proper ear mould identification is critical. These fungi not only reduce yield but produce mycotoxins impacting feed value, marketability and livestock health!
Source: OMAFRA