Update on Corn Ear Moulds and Vomitoxins – Greg Stewart from Maizek Seeds


1.  Why this year?

The risk for ear moulds and the presence of the inoculum in the environment which causes the infection is present every year.  Mould gets started via the silks or by some damage to the ear. In all cases, frequent rains or high humidity in the post-silking period (late July – August) leads to more initial infection and a greater likelihood that the mould occupies more space on the ear.  This year Western Bean Cutworm damage is considerably down from previous years and in most cases it appears the mould infection entered the ear via the silk channel and not from widespread ear damage.

2.  Why my field?

Frequent rainfall and high humidity in the period 7-21 days after corn tasseling is the basis for ear mould and high toxin levels. In addition, corn hybrids are showing a large range in susceptibility to mould development. Hybrids that have a longer husk cover or husks that remain tighter to the ear seem to be prone to greater mould infection. Later emerging plants that have reduced ear size and more husk cover, or the second smaller ear on a plant all seem to be adding to the problem.  In addition, stressed plants from compaction, drought, and low fertility also tend to have more ear mould in any given field.

3.  Where in Ontario is the problem worse?

The problem is quite wide spread across southwestern Ontario. Traditionally the Chatham-Kent and Essex area has struggled with the most consistent ear mould/mycotoxin risk but in 2018 many areas further to the east (i.e. Oxford, Middlesex, Perth, Waterloo, Brant, etc.) are severely impacted. Even areas east of Toronto and in to the Ottawa Valley are showing some elevated risk this year.

See the OMAFRA survey map for some more details.


4.  What is the relationship between visual mould and toxin?

Generally speaking the amount of white or pink-coloured mould (Giberella) on the ear is fairly well correlated to increasing DON in the grain.  However, there are some exceptions.  In some cases, the mould is less obvious and runs down between the kernel rows but can result in high DON levels.  In other cases the mould is very obvious and has a black or green appearance but may not be associated with mycotoxin production.  Test to be sure.

5.  Can I change toxin scores by harvesting, cleaning or drying techniques?

Careful combine set-up is the first line of defense.  Do everything you can to exclude fines, cob parts and smaller, infected kernels.  Concave, screen and wind speed settings can all contribute to lower vomitoxin levels.  If, for whatever reason, the sample comes from the field relatively dirty then a separate cleaning operation can lower vomitoxin scores.  However, once a sample is clean do not expect the drying operation or further cleaning to have significant impact on DON levels.

6.  Will toxin increase after harvest?

Wet grain sitting in a bin may increase in vomitoxin levels especially if temperatures are above 10 C.  Mould growth and mycotoxin production ceases below 15% moisture.  Ensure that all stored grain is thoroughly dried, and growers should target a final moisture of 14.5 % to avoid hot spots. Fines that concentrate in the center of the bin should be removed early to maintain the integrity of the entire bin.

7.  What is the role of crop insurance?

Agricorp considers plant disease an insured peril and therefore elevated vomitoxin (DON) in a grain sample is eligible for coverage.
Agricorp may write off; assign a zero yield to unmarketable crops affected by DON, upon written proof of rejection letters from elevators or other grain receivers.

See the following link for more details and contact your crop insurance adjuster to discuss your situation.


8.  Why do I have moulds even after spraying with a fungicide?

Some growers have been perplexed that they have an ear mould problem even after spraying all their corn with a fungicide application at tassel time.  It is important to remember that only the fungicides Proline and Caramba have any impact on ear moulds and resulting vomitoxins.  So if you sprayed some other fungicide product it may have reduced leaf diseases and improved yields but has had no impact on your DON levels.

9.  What plans should I employ for harvest?

The important message is to scout fields, harvest samples and check DON levels so that you can prioritize harvest.  In some cases where fields have low DON levels (< 3 PPM) and is standing well these fields could be left for other fields that have elevated DON levels (i.e. 3-7 PPM).  These elevated DON fields need to be segregated and if possible harvested, dried, or marketed as quickly as possible.

Do not mix clean corn with higher levels of DON corn.

High DON fields (8 PPM or over) will pose a greater challenge.  In these cases crop insurance may be an option or watch markets to see if other opportunities emerge for higher DON grain corn.
Be careful to note that headlands that have additional stress or bird or insect damage may have DON levels that are higher than the rest of the field.  Avoid using headland grain as the determination for the entire field’s marketability.

10.  How do I move forward with this problem in the future?

Since hybrid selection is one of the key management factors be sure to discuss hybrid options for 2019 with your Maizex representative that can potentially reduce your exposure to ear mould.  Increasing hybrid diversity can contribute to a wider silking window and reduce the infection risk connected with a particular weather period.

Moving forward increased attention to plant stand uniformity and fungicide applications that specifically align with ear mould reductions will be additional priorities.

Download the PDF below.


Greg Stewart,
Maizex Seeds

Keep up to date on agronomy information and news at maizex.com featuring tips and ideas from Greg Stewart, Agronomy Lead.


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