Plan to Assess Field for Ear Rot and Mycotoxin Risk
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.
Gibberella Ear Rot
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 and can survive on soybean roots. Gibberella in most cases begins at the ear tip and works its way down the ear plus the husks from infected ears are often tightly adhered to the ear (Figure 1). Although the fungus can produce a white-coloured mould which makes it difficult to tell apart from Fusarium Kernel Rot, the two can be distinguished easily when Gibberella produces its characteristic red or pink colour mould. Infection begins through the silk channel and thus, in most cases starts at the ear tip and works its way down the ear. In severe cases, most of the ear may be covered with mould growth. Corn silks are most susceptible 2–10 days after initiation. Warm and wet weather during this period is ideal for infection.
Figure 1. Gibberella ear rot – Red/pink mould which often begins on ear tip
Fusarium Kernel Rot
Unlike Gibberella, Fusarium infected kernels are often scattered around the cob amongst healthy looking kernels or on kernels that have been damaged for example by insect injury or bird feeding. Fusarium infection produces a white to pink or salmon-coloured mould. A “white streaking” or “star-bursting” can be seen on the infected kernel surface (Figure 2). 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). Fusarium survives in corn debris. The significance of this fungus is that it produces a toxin called fumonisin that has been shown to cause cancer (carcinogen) in humans. The environmental conditions that favour disease development are warm, wet weather 2–3 weeks after silking.
Diplodia Ear Rot
The characteristic ear symptom of Stenocarpella maydis and S. macrospora infection is a white mould that begins at the base of the ear and will eventually cover and rot the entire ear (Figure 3). 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. Pycnidia (the small, black, spore-producing structures of the fungus) overwinter on corn residue and are the source of infection for the subsequent corn crop. Dry weather before silking, immediately followed by wet conditions, favor Diplodia infection.
Figure 3. Diplodia ear rot – Mould begins at base
Penicillium Ear Rot
Penicillium rot (Penicillium sp) produces a light blue-green powdery mould which grows between the kernels and cob/husk surface (Figure 4). Infected kernels could become bleached or streaked. It can be a serious problem if corn is stored at high moisture levels (greater 18%).
Figure 4. Penicillium ear rot – Mould between kernels and on cobs/husk
Table 1. Common ear rots and moulds that occur in Ontario and the primary mycotoxins they produce
Corn Ear Rot
(Gibberella zeae, also called Fusarium graminearum (asexual stage))
|· Red/pink mould
· Begins on ear tip
· Bird, insect injury increases damage
|· Deoxynivalenol (Vomitoxin or DON)
· Zearalenone (ZEN)
· T-2 toxin
|· White, pink or salmon coloured
· Can occur anywhere on ear
· Often begins at the sites of insect damage
|· White mould
· Begins at base of ear but often entire ear covered
· Black pycnidia (bumps) on husks and kernels
|· Blue-green mould
· Mould between kernels and on cobs/husk
More information can be found in OMAFRA’s Field Crop Agronomy Guide – Publication 811, or Crop Protection Network Publication “Corn Management Disease Series – Ear Rots” at CropProtectionNetwork.org or on the Grain Farmers of Ontario Website (http://gfo.ca/Production/Production-Resources).
Photo credits: Crop Protection Network
Table 2. September 13 – 19, 2017 Weather Data