7 READ-TIME

Stay on top of corn issues to protect yield

November 13, 2023

corn field and blue skies in the Midwest

Corn growers in Canada have likely invested more in their corn crop this year than ever before. But with high prices and plenty of demand, that investment has the potential for big payoffs — if farmers can get that crop to a successful harvest.

Over the past decade corn has become an increasingly important crop for Canadian farmers, but with more acres comes more problems. In order to get the yields corn growers need for a return on investment, they need to protect it against problematic weeds, disease and pests throughout the season. Most issues are regional, weather dependant or both, and require a watchful eye to make sure they don’t take a bite out of the bottom line.

“Successful corn growers need to be aware of what is going on in their fields,” says Ron Rabe, market development agronomist with Bayer. “Walking the fields will let them know what they are facing but will only give them a front row view. Using a program like Climate FieldView will let them drop a pin on anything suspicious. They can also pull back leaves and see what they are facing and keep on top of any potential problems.”

CONTROL WEEDS EARLY

Early weed removal in corn is absolutely critical to protecting yield. Corn is well known to be an incredibly poor competitor in its early stages. Indeed, most farmers growing corn in Canada are aware of research out of the University of Guelph, a decade or so ago, that showed emerging seedlings can detect the presence of aboveground weeds and will actually change their morphology in an effort to avoid them, thereby making more room for weeds.

The impact on yield can be enormous, with some studies showing as much as a 50 per cent yield loss when weeds are not controlled during the critical weed-free period, which is from emergence to the 6- to 8-leaf stage. Using a pre-emergence herbicide with some residual activity is key.

“Corn growers quickly learn the impact of weed control on corn in the early development stage of the crop,” says Greg Stewart, agronomy lead with Maizex Seeds. “You are much better off to spray early and live with a few later weed escapes than to wait for all the weeds to emerge (before spraying) and then you’ve lost up to 15 bushels of yield potential.”

“Successful corn growers need to be aware of what is going on in their fields” RON RABE, MARKET DEVELOPMENT AGRONOMIST BAYER

BE ON THE LOOKOUT FOR TAR SPOT

Disease in corn is generally dependent on the region, weather conditions and whatever happens to blow in every season.
Tar spot is on many corn growers’ radar as it was first confirmed in Ontario late in 2020 and by 2021 the disease was found throughout southwestern Ontario all the way to north of Toronto. The spores spread easily and over long distances, so crop rotation is not a management option. While the disease is still relatively new to Canadian corn growers, U.S. growers have seen yield losses from tar spot of 25-35 per cent.

“You don’t want to miss early development, as it can be first identified the first week of July,” says Stewart. “That’s usually when corn growers are taking a breath, but now they have to identify any signs of tar spot so as not to miss an application window. Early identification is key, and you need to be prepared to spray.”

Fungicides, especially those with multiple modes of action, help slow damage from the disease and for those in areas where tar spot is a problem, a fungicide is likely already a necessary part of a grower’s disease management strategy. In those same areas, growers use foliar fungicides to manage gibberella ear rot, which although a longstanding concern, doesn’t strike every year.

Northern corn leaf blight (NCLB) is the most common foliar fungal disease of corn. It first appears on the lower leaves and spreads to the upper canopy where it looks a little like frost damage. NCLB can cause yield losses up to 20 per cent and is constantly developing new races and new fungal pathogens, so staying on top of this one is key to preserving yield.

“Traps and scouting will help make sure you are spending less time on unnecessary insecticide applications and help get the most out of your investment” TRACEY BAUTE, ENTOMOLOGIST OMAFRA

CORN ROOTWORM MOVES WEST

Corn rootworm, a common problem in eastern corn growing regions, was recently found in Manitoba, so western growers can learn from their eastern colleagues. Frustratingly, corn rootworm incidence can be difficult to predict from one year to the next. “It doesn’t matter if you are growing corn for the first time or are in a field that has had back-to-back corn,” says Rabe. “Your best protection is to plant a Bt-Corn that has insect protection built into the genetics so rootworm can’t do any damage.”

And yet there is evidence in Ontario and Quebec that Bt protection can break down. Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) entomologist Tracey Baute runs a trapping program (funded by the Grain Farmers of Ontario) to monitor and quantify the presence of Bt-resistant rootworm in Ontario. “Even if the damage is mild now, the larvae will continue to build up and become a bigger problem, especially in continuous cropping systems, which are more common when corn is grown for livestock feed,” she says. “Corn can lose up to 50 per cent of its yield, which can be a big problem when you are using it to feed your livestock.”

Baute says it is important for growers to flag where and when they identify injury from corn rootworm so OMAFRA can further investigate, collect larvae to be tested for resistance and determine if populations are spreading. She says that while the issue is manageable right now, looking to the U.S. for perspective shows how problematic the pest can become. There, resistance is widespread.

“We are able to monitor the [adult] beetles and track when peak activity occurs,” Baute says. “We can also investigate further when new areas crop up with higher-than-normal populations. We can help the grower determine if they have a population resistant to the Bt traits so they can come up with a plan of action for subsequent seasons.”

There has been some success managing resistant rootworms through the introduction of biocontrol nematodes that are sprayed on the soil. Evidence shows that this protection lasts 10 or more years and will help preserve the use of Bt corn traits.

WESTERN BEAN CUTWORM STILL AN EASTERN PROBLEM

European corn borer in situ.

Despite its name, Western bean cutworm is mainly a problem for eastern corn growers, causing feeding damage on corn ears. While the yield loss isn’t generally as significant as with other pests, those wounds create an entry point for moulds and mycotoxins, which can lead to serious disease and downgrading.

Western bean cutworm is monitored through trapping adult moths when they are active. “Even if you use an insecticide you should still scout later in the season to look for damage,” says Baute. “There is such an extended moth flight that a one time application can’t get them all. Scouting will help determine if you need to consider harvesting early to reduce your risk of mould development.”

Climate change has shifted the migration habits of insects, so Baute is always vigilant for what is potentially on the horizon from corn crops in U.S. border states. “We look at what is overwintering in the States, set traps and just keep track of migration patterns to see what is feeding on the ears of corn south of us, and see what we should be aware of,” she says. “We have been watching for Asiatic garden beetle but we haven’t had reports of it as yet.”

“Your investment in your corn crop is high,” concludes Baute. “Traps and scouting will help make sure you are spending less time on unnecessary insecticide applications and help get the most out of your investment.”

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*Performance may vary from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the growers’ fields.