Generally dry conditions have reduced the threat of mycotoxins in corn this year, although rains during humid days could change that as corn moves to tasselling and silking.
However, Dave Hooker, of the University of Guelph’s Ridgetown College, says that historical monitoring of mycotoxin levels by the Ontario Ministry of Agriculture Food and Rural Affairs shows that there are definite hot spots in the province.
There are also hybrids that are more susceptible, he said, no matter what seed companies tell you.
Why it matters: Corn mycotoxin levels are an important determinant of quality. Increasingly farmers are spraying insecticides to protect corn from insects that cause wounds that result in mould and fungicides to protect from silk channel infection.
Hooker spoke at the recent Bayer CropScience Dead Weeds Tour near Guelph.
He worked on a model for corn similar to the DONCast system for wheat that predicts mycotoxin pressures based on weather trends, but it didn’t work out.
The researchers looked at corn samples, weather history and production history around those samples and tried to create a model that could help predict mycotoxins in corn, but “I was never happy with the DONCast predictions for corn,” he said.
There are several other factors involved with corn that aren’t involved with wheat and barley, especially the impact of seed pressure on corn mycotoxins.
The best information has resulted from high corn mycotoxin levels seen in 2006 and 2011.
The good news is that the disease can be managed and therefore, the risk from mycotoxins reduced.
High levels of mycotoxin in corn are especially a concern when feeding pigs and poultry. High levels of infection in corn can result in lower gain in pigs and abortions in sows.
Corn high in mycotoxins can be hard to market.
In 2011, 24 per cent of 1,500 corn samples taken around Ontario tested over two parts per million, well over the concern level of one part per million.
Mycotoxin levels in 2012, 2013 and 2014 were over two parts per million less than 10 per cent of the time and in 2015 over two parts per million five per cent of the time. In 2016 and 2017 levels were high again, he said.
All those years show pockets with high levels of mycotoxins.
“We have to stay up on our game in order to manage this,” he said.
One of the first places to start is in managing hybrid selection.
Dr. Art Schaafsma’s group at Ridgetown College looked at 30 corn hybrids over three years. It showed some hybrids were quite sensitive to mycotoxins.
“The hybrid is definitely important. If you are a hog producer with a history of high DON levels on the farm, I would suggest to talk to your seed dealer for hybrids with a fairly low risk of accumulation.”
DON is deoxynivalenol, one of the common mycotoxins that occur in grains.
Hooker said hybrid differences year to year are too great from the Ontario corn hybrid trials and so corn seed companies haven’t had the confidence in the numbers to make them public.
Growers need to manage the pathogen, the host, or the environment in order to break the ability of the pathogen to grow.
Fusarium graminearium enters the corn plant in several ways. The spores land on the silks, called silk channel infection. Luckily the time of infection is only from when the silks emerge until they brown, so the risk will have a lot to do with the environment.
Spraying for control of silk infection with products like Proline ends when the silk browns, although the plants can also still be sprayed for other reasons.
Some years, especially dry ones, slow pollination can mean a longer risk period for fusarium.
Wounding is the second point of infection, which can be from insects, hail or application of late nitrogen. The wound has to be on the cob.
It’s the silk channel infection where fungicides are most useful, not the wounding, Hooker said.
At harvest time, you can identify how the disease entered the ear. Silk channel infections are mostly seen closest to the tip of the cob. Infection from wounding is more variable across the crop.
Insecticides are the other way to protect a crop – by limiting the insect wounding of the cob, especially from Western Bean Cutworm (WBC), not considered the largest economic-impact pest in the province.
Luckily, the WBC pressure appears to be average or lower this year, compared to other years.
The only insect resistance trait that works on WBC is Vip3. The Cry1F traits in most corn provide no protection from WBC.
How to scout for WBC
Don’t spray on WBC moths. Spray according to egg counts from scouting begun at tasselling. Find 20 plants in five areas of the field and if there is greater than five per cent of counts with eggs on them, it would trigger a spray decision. Scouting is also cumulative. If it’s one per cent on the first scouting trip, and three per cent five days later, then that means four per cent is counted.
“We think if a hybrid is quite sensitive then we should be reducing that threshold to two per cent, especially during favourable weather conditions at silking.”
Favourable weather conditions include warm foggy mornings.