Traditionally An Eye On Ears
by Greg Stewart, OMAFRA Corn Specialist

Figure 1
Giberella ear rot infection usually occurs from the tip down. Note the dark pink to red colour.
Ear mould on corn has been a long-time concern to corn growers within the province, especially those that feed the vast majority of their corn to livestock. The conditions that lead to ear mould problems in the grain are not very well understood. The last significant occurrence of ear mould was in 1999. This was a surprise to most since that growing season was dominated by hot dry conditions and not the type of weather we would expect to foster ear mould growth.

Although the reasons for these sporadic and sometime unexpected ear mould outbreaks are unclear it may be related to one or all of the following:

1) poor ear fill, predisposing the ear to infection
2) heat and drought stress
3) a large number of foggy or mist-filled mornings in August and September (moisture enhances infection possibilities)
4) ear damage by insects creating infection entry points

As I write this article, about the only thing that I am sure of is that in the 2003 growing season we had more than our share of high humidity and foggy mornings during the pollination and early grain–fill period. Insect and bird activity on the ears was perhaps slightly higher than normal as well.

Hopefully, dry conditions in September and on into the harvest season will suppress any mould growth. However, as a precaution, corn producers are advised to scout fields for ear mould. Fields should be first targeted for scouting where the crop has been under more stress than normal, or where insect or bird damage had been noticed earlier in the season. You may also consider targeting fields where wheat was grown last year as having the potential for greater infection. Scouting 5 fields may reveal 4 mould-free fields and one with severe mould. Infection in fields is sporadic, often field specific. In addition, some hybrids appear more prone than others to fusarium. In fields where there is no mould growth there is no risk of mycotoxin production.

The most common and important ear mould in Ontario is Gibberella zeae, which is the sexual reproductive stage of Fusarium graminearium. This fungus not only infects corn but also small grains such as wheat, where it causes Fusarium Head Blight.

Although, the Gibberella fungus can produce a white mould that makes it difficult to tell apart from Fusarium ear rot, the two can be distinguished easily, when Gibberella produces its characteristic red or dark pink (purple) mould (Figure 1).

Infection begins through the silk channel and thus, in most cases starts at the ear tip. In severe cases, most of the ear may be covered with mould growth. Corn silks are most susceptible 2-10 days after initiation, and hence the concern over cool, wet or high humidity weather during this period.

Gibberella ear rot is economically important not only because of the potential yield and quality losses but because Gibberella zeae and Fusarium graminearum produce two very important mycotoxins that occur in Ontario - deoxynivalenol (vomitoxin or DON) and zearalenone. These mycotoxins are especially important to swine and other livestock producers since they can have a detrimental effect on their animals. Feed containing low levels of vomitoxin (1 ppm) can result in poor weight gain and feed refusal in swine. Zearalenone is an estrogen and causes reproductive problems such as infertility and abortion in livestock, especially swine. Feed grain that originated in a field with 5% or more Gibberella ear rot should be tested for these toxins.

If you encounter mould problems, it does not necessarily mean that the mycotoxins (i.e. vomitoxin, zearalenone, fumonisin, T-2) produced by the moulds are present yet in the grain. The likelihood of mycotoxin production increases on corn where the mould is deep pink or purple in colour. Samples should be taken and sent to a lab for mycotoxin analysis. Also remember, mycotoxins, depending on their concentrations in the feed can be readily detected on the farm. Zearalenone in feed eaten by eight week old gilts will cause redness and swelling of the vulva in 4 to 10 days. Similarly, vomitoxin or T-2 may result in noticeably reduced feed intake in 8-week-old piglets after just a few days on the infected feed.

Harvest Precautions to Minimize Impact of Fusarium Infected Corn

There are several precautions that can be undertaken during harvest to reduce the impact of fusarium infected corn.

1. First, harvest infected fields early. Mycotoxin levels have the potential to build the longer you leave the corn in the field. Once corn moisture is below 18%, the fusarium fungus is dormant and ceases to produce mould.
2. High temperature drying stops mould growth and mycotoxin production but does not reduce mycotoxins already present. Quick drying is preferred over low heat drying. Be wary of low temperature in bin dryers for mouldy corn and be sure proper ventilation requirements are met for storing dry corn. Keep in mind that there is moisture variability across the field, therefore, wet pockets above 18% moisture can still produce moulds.
3. Set the combine to provide high levels of wind to blow out the lighter infected kernels. The fusarium fungus results in lower kernel stability, resulting in higher incidence of mycotoxins in fines (kernel tips and red dog) and cob pieces.
4. Sacrifice the tip kernels by running the combine at full capacity with concave settings wide open and cylinder speed set low. Screens on the bottom of the grain elevator, the bottom of the return elevator and on the unload auger will also help screen out the fines.
5. In corn silage, the acids produced during proper ensilage will stop the growth of moulds. Where there is improper fermentation, moulds could continue to produce mycotoxins and lead to higher toxin levels that could affect cattle.

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