STORAGE MOLDS IN CORN

by Albert Tenuta, Field Crop Plant Pathologist, OMAF Ridgetown

Preventing ear rots and mold is difficult since weather conditions are critical to disease development and although some tolerant hybrids are available none have complete resistance. Wet conditions, like we experienced this fall that result in a delay in corn harvest can lead to increased ear rots and molds. The longer the crop is left in the field under these conditions, the greater the potential for disease development. Small to almost non-detectable levels of mold in the field can lead to significant mold problems if they go unnoticed and are allowed to develop in storage.

The three primary ear molds that occur in Ontario are:
Gibberella Ear Rot, Fusarium Ear and Kernel Rot and Diplodia Ear Rot. Hybrid genetics and environment can impact disease symptoms.
Gibberella and Fusarium Ear Rot: These two fungi not only cause our most important ear molds but can lead to significant stalk rot and mycotoxin problems as well. The most common and important ear mold in Ontario is Gibberella zeae which is the sexual reproductive stage of Fusarium graminearium. Although, the fungus can produce a white colour mold which makes it difficult to tell apart from Fusarium ear rot, the two can be distinguished easily when Gibberella produces it's characteristic red or dark pink (purple) colour mold. Conversely, Fusarium infection produces a white to pink or salmon-coloured mold with a "white streaking" or "star-bursting" appearance 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 (formerly Fusarium moniliforme).
Diplodia: It is the least common of the three primary ear rots that occur in Ontario. It is caused by the fungus Stenocarpella maydis (Diplodia maydis) and it favours cool, wet conditions through grain fill. The characteristic ear symptom is a white mold that begins at the base of the ear and will eventually cover and rot the entire ear. Mold growth can also occur on the outer husk which has small black bumps (pycnidia) embedded in the mold. These reproductive structures are where new spores are produced. Unlike Gibberella and Fusarium, Diplodia does not produce any known toxins.

In addition to Fusarium, Gibberella and Diplodia, four other fungi cause storage molds in Ontario. Penicillium, Aspergillus, Cladosporium and Alternaria can be found in varying amounts each year. Knowing what to look for can help you tell them apart?

Penicillium and Aspergillus can occur in the field and in the storage. Although they are difficult to tell apart, they do produce a slight difference in colour. Penicillium is a blue-green powdery mildew while Aspergillus is a gray-green or yellow-green coloured mold. The symptoms range from mold growth on the kernel surface to internal discolouration of the embryo ("Blue-eye mold"). Discoloration of the germ indicates kernel death as well as the presence of blue eye indicates that the grain has been improperly stored.

Alternaria and Cladosporium produce a black mold and are considered "opportunist" fungal pathogens. They thrive when harvest conditions are delayed, injury from insects/birds, or premature crop death from frost occur. All of these conditions can be found this fall.

Storage molds can reduce feed value, marketability as well as lower germination, discolour the seed, cause caking, heating and bin-bumed com. Some of these fungi (Fusarium, Gibberella and Aspergillus) can produce certain toxins and pose a risk not only to livestock but to human health.

Increasing stored grain quality is like searching for the "Holy Grail". It is a noble endeavour but highly unlikely to succeed. The best you can hope for is preventing or slowing the development of molds in stored corn through aeration, maintaining proper temperature and moisture content, controlling insects, minimizing mechanical injury, cleaning the bin, regular inspection and removing broken kernels or fine grain particles. Although all of these points are critical, the importance of clean grain is often undervalued. Fines and broken kernels are ideal locations for mold growth to begin and subsequently spread to the healthy grain.

Although most of these diseases start in the field they may not be easily seen. It is important to examine your grain sample before it goes into storage. Moderate temperature and high relative humidity in storage will increase these fungi and the rots they cause. In severe cases, drying or finding a quick use for the com is advisable. Stored feed grain that has mold or originated in a field with 5 to 10% of Gibberella or Fusarium ear rot should be tested for mycotoxins.