Plan to Assess Field for Ear Rot and Mycotoxin Risk OMAFRA Field Crop Team

With assistance from the Ontario Agri Business Association (OABA) and funding through the Grain Farmers of Ontario, Ontario Ministry of Food and Rural Affairs (OMAFRA) and Agriculture and Agri-Food Canada (AAFC) will begin sampling grower corn fields to determine ear mould incidence and occurrence of mycotoxins in the grain.  These mycotoxins, particularly vomitoxin (DON) produced primarily by Gibberella/Fusarium ear moulds can be disruptive when fed to livestock, especially hogs.  The purpose of this annual survey is to access grower and industry risk.

What can growers do? As corn producers plan for harvest they should be assessing their fields for stalk rot and ear moulds. The distribution and prevalence of these diseases vary from year to year but they are present every year, especially when the crop is planted late or under stress (water stress, insect feeding, etc).  Growers should assess fields each year, because these pre-harvest assessments can alert them to potential problems and provide time for livestock producers to segregate, obtain alternative grain, or hold onto stored corn from the previous year.

Scouting practices are similar for all corn ear rots. Begin scouting fields at late dent stage to determine the presence and severity of ear rots. When scouting, randomly select plants and pull back the husk to examine the entire ear. A quick method is to select 100 plants across the field (20 ears each from five different areas). For each ear, be sure to peel back the husks and examine the entire ear. Fields with 10% of ears having significant mould growth should be harvested sooner than later.

Leaving diseased grain in the field allows the ear rot fungi to keep growing, which will increase the risk of mouldy grain and mycotoxin contamination (Table 1).  Most ear rot fungi continue to grow (and potentially produce mycotoxins) until the grain has less than 15 percent moisture. In severely infected fields, it may be worthwhile to harvest grain at higher moisture and then dry it to less than 15 percent to minimize further mycotoxin accumulation.  If a field contains a significant level of ear mould, collect a representative sample at harvest and have it tested for mycotoxins before storing the grain or feeding it to livestock. A lab test is often the only reliable way to definitively diagnose an ear rot or mycotoxin.

Preventing ear rots and mould can be difficult since weather conditions are critical to disease development. Although some tolerant hybrids are available, none have complete resistance. Crop rotation reduces the incidence of some ear rots, as well as, several foliar fungicides aimed at suppressing ear rots have been registered. Cultural practices have been shown to have limited success in preventing ear and kernel rots. Minimize these diseases through timely harvest and proper drying and storage.

When ear rot is present, the following storage and feeding precautions are advisable:

• •    Harvest as early as possible
• •    If insect or bird damage is evident, harvest outside damaged rows separately. Keep and handle the grain from these rows separately.
• •    Adjust harvest equipment to minimize damage to corn. Clean corn thoroughly to remove pieces of cob, small kernels and red dog.
• •    Cool the grain after drying
• •    Clean bins before storing new grain
• •    Check stored grain often for temperature, wet spots, insects and mould growth
• •    Control storage insects
• •    Exercise caution in feeding mouldy corn to livestock, especially to hogs. Pink or reddish moulds are particularly harmful. Suspect samples should be tested for toxins.

As mentioned earlier, it is critical to identify ear rots in the field because many of the fungi responsible for these diseases produce mycotoxins which can not only harm livestock and humans but contaminated grain can be difficult to market and may be docked in price. Management begins with proper identification so how can a grower tell the difference between these ear moulds.

Source: OSCIA