Determine Your Ear Rot & Mycotoxin Risk

by Albert Tenuta, OMAFRA, Field Crop Plant Pathologist

Weather conditions, such as those experienced in 2006, can be favourable for corn ear mold fungi. This alone is sufficient to cause concern amongst corn producers. The extent of pink ear rot damage (aka Gibberella ear rot; Fusarium graminearum) together with the number of such ears in the field is proportional to the concentration of vomitoxin in the harvested crop. In affected areas, there is also the potential for accumulation of the mycotoxin zearalenone. This has been a less common problem in Ontario corn in the last 20 years but there were years in the late 1980s in which zearalenone concentrations were relatively high.

For these reasons, exercise caution in feeding moldy corn to livestock, especially to hogs. Grain with pink or reddish molds is particularly harmful. Suspect samples should be tested for toxins, especially Deoxynivalenol (DON) prior to storage and feeding. If necessary, feed to less sensitive livestock species such as beef cattle or poultry.

Check all your fields carefully and note their current condition. Be sure to check for differences due to hybrid and planting date; in some cases these factors have had a large influence on the amount of mold infection.

A quick method includes scouting 100 plants from the field (5 areas of 20 ears each). Fields with 25% of the ears having mold growth should be harvested sooner rather than later. The production of toxins is a major concern when these ear rots are present but it is not always the case that mold growth equates to high toxin levels and vice versa (high toxin levels can occur with little visible fungal growth or ear rot). It is
essential to examine a field and determine which ear molds and mycotoxins are present. This will allow for the implementation of grain harvest, storage and feeding management options to minimize toxin development and maintain grain quality.

Livestock producers should concentrate on fields with the highest quality and focus on harvest/drying those first in a timely manner. For dry corn, dry to less than 18% as quickly as possible. This will help maintain quality, reduce fungal growth and limit further increases in mycotoxin levels since both DON and zearalenone production will stop.

Some other considerations are:

1. If bird damage, lodging, corn borer etc has increased ear molds, if possible, harvest these areas separately
(for example, harvest non-Bt IRM corn refugia separately). Keep and handle the grain from these areas separately as well.
2. Tight husks often enhance the risk of field outbreaks of Gibberella ear rot by retaining moisture inside the ear.
3. Zearalenone (ZEN) is mainly produced when the pink ear rot fungus continues to grow under cool wet conditions after grain maturity. Once corn is harvested, drying it quickly is very important because ZEN can be produced rapidly in wet tanks and in parts of wet tanks which may have grain clumping.
4. Gibberella ear rot resistant or tolerant commercial corn hybrids can reduce disease and potential mycotoxin production. For next year, check with your seed corn company not only for hybrid ear mold ratings but other stresses such as leaf disease resistance,
insect resistance, etc that could increase ear mold problems under favourable conditions. In addition, consider planning a multiple hybrid on-farm strip trial in the future which compares various hybrids under your specific field conditions.
5. The longer the corn is allowed to remain in the field the greater chance of mycotoxin development. Therefore, do not leave corn in the field through the winter to save on drying costs.