The number of corn acres in Western Canada is growing.
Grain corn acreage in Western Canada nearly doubled in a recent 15-year span, rising from 210,000 acres in 2007 to slightly more than 414,000 in 2022, according to data compiled by Agriculture and Agri-Food Canada. The trend has continued into 2023.
While that development is good news, it suggests there could be a corresponding rise in corn disease incidence, says a plant researcher with the Manitoba Crop Alliance (MCA), which represents corn growers in the province.
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“I think that with corn acres going up you obviously will see more disease pressure because there are more hosts available,” says Madison McCausland, research program manager of special crops with the MCA.
“It is something that we must have on our radar and we want to be ahead of that curve versus having an epidemic and getting into a situation where we don’t have any tools to mitigate those kind of disease pressures.
“While disease in corn isn’t biggest issue among all of the crops, it is something that we are conscious of and have to be aware of.”
GOSS’S WILT
Perhaps the biggest disease concern on the Prairies is the bacterial disease known as Goss’s wilt. It’s caused by the bacteria Clavibacter michiganensis subsp. nebraskensis. It typically occurs when there is injury to the plant’s leaves caused by wind, hail or sandblasting, which allows bacteria to enter.
Symptoms include leaf discoloration and necrosis. Because the leaves cannot effectively draw in sunlight to create the nutrients required, Goss’s wilt can severely reduce overall yield.
McCausland says a 2016 disease survey in Manitoba showed the bacteria was present in a third of fields surveyed. That percentage would likely be higher today because corn acres in that province have continued to grow, she adds.
It’s also likely to have a greater presence in Saskatchewan and Alberta, since corn acres in those two provinces have also significantly increased.
“As we’re getting a lot more corn grown in these areas, we’re going to start seeing a lot more incidence of this happening as we move west and corn is becoming a more popular crop in these western provinces,” McCausland says.
Goss’s wilt is challenging to manage because it cannot be treated with fungicide.
McCausland says prevention is the best tool for managing its spread, and residue management is among the most effective tools because the disease tends to thrive in stalk residue.
A more diversified crop rotation can also help.
“Crop rotation is really key,” says McCausland. “In Manitoba, we’re a little spoiled and we’ve got away with not worrying about that so much. Some guys will grow corn on corn on corn.
“However, as disease pressure grows, the more you do that, the bigger the problem it’s going to become.”
Few varieties are tolerant to Goss’s wilt. McCausland is hopeful that will change soon, in part because of research and breeding efforts in Manitoba.
“That’s going to be really important for crops and for the farmers selecting varieties.”
GIBBERELLA EAR ROT AND STALK ROT
Gibberella ear rot is just as nasty as it sounds. It’s an ear mould caused by the fungal pathogen Gibberella zeae. It’s the same fungus that causes fusarium head blight in cereal crops such as barley, oats and wheat and can ultimately destroy the only part of a corn plan that is harvestable.
Symptoms include rotting of necrosis of the ear as well as the presence of a white powder with a pink hue.
To make matters worse, the fungus that causes Gibberella ear rot produces the mycotoxin deoxynivalenol (DON). The threshold for DON is extremely low for both human and animal consumption.
“If you’ve got an amount of this mycotoxin that is higher than this threshold, it essentially means that your entire yield is garbage because the mycotoxin is so toxic you can’t feed it to humans… or to animals. You can’t do anything with it because it is so toxic,” says McCausland.
If growers detect the presence of Gibberella ear rot, she advises that they harvest that area immediately to prevent spread and save as much of their crop as possible.
As is the case with Goss’s wilt, prevention is the best way to manage the spread of ear rot. That means close attention to crop rotation, McCausland says, and avoid growing a cereal and corn immediately afterward because the fungal pathogen can be easily transferred from the first crop to the latter.
Gibberella stalk rot is similar to ear rot in the sense that both are caused by the same pathogen. It can reduce corn yield by killing the plant before it is mature. It can also cause lodging, which can increases yield losses and hamper harvest efforts.
Its symptoms are similar to those of Gibberella ear rot. It causes browning of the stem and creates the same pink powdery substance within the stalk, which indicates the presence of the dangerous mycotoxin.
McCausland says it can be difficult to detect the presence of stalk rot unless you are close to an infected plant.
As with ear rot, good residue management and a diversified crop rotation are the best ways to control it.
RUST AND SMUT
Two other corn diseases present on the Prairies are rust and smut. Although neither poses a serious risk now, McCausland said growers should keep on top of them and avoid complacency about either disease.
Rust produces rust-coloured pustules on a corn plant’s leaves. In severe cases, it can cause leaf chlorosis and kill the plant. Rust isn’t a major concern on the Prairies, McCausland says, because several fungicides are available to deal with it as long as it is detected early.
Smut is a fungal pathogen. It’s common in most areas where corn is grown but generally doesn’t cause significant economic losses.
It’s essentially a fungal growth and similar to mushrooms. In fact, in many Central American countries, it’s regarded as a prized delicacy. It appears as a gall or abnormal growth throughout the growing season on any above-ground part of the plant. In some cases it can completely destroy the cob.
McCausland says the best defence against smut is choosing a newer variety that has resistance.
“If you’re growing resistant varieties, like current hybrids that have resistance to them, you won’t necessarily have to worry about a problem. If you’re growing resistant varieties and you have one, you’re probably not going to get an infestation. It might just be a one-off. Just make sure you’re growing current varieties that have resistance incorporated.”
