Seed & Chemical
Eyespot in Ontario corn
By Julienne Isaacs
Ontario corn growers should be on the lookout for eyespot this season, warns Albert Tenuta. Photo courtesy of Krishan Jindal.
It might not be Ontario’s flashiest foliar disease on corn, or even the most economically devastating – both those awards go to Northern corn leaf blight – but eyespot was on the rise in 2015, and may be a cause for concern for Ontario growers in 2016.
According to Albert Tenuta, field crop pathologist for the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), eyespot is “one of those diseases that looks worse than it actually is – the impact on the corn is minimal.”
But it’s certainly not negligible. Common in the northern regions of the corn belt, eyespot becomes a problem in fields with residue from previous crops, or in continuous corn cropping. Caused by the fungus Aureobasidium zeae, infection generally occurs in the spring under cool, wet conditions; if it spreads to the upper leaves of the plant, it can cause reduced yields.
Tenuta is a member of Agriculture and Agri-Food Canada (AAFC) and OMAFRA’s annual corn disease survey team. Each year, on average, 200 corn plots across Ontario and occasionally Quebec are tested for major corn disease severity.
According to survey team member Krishan Jindal, a pathologist with AAFC’s Ottawa Research and Development Centre, the survey is a valuable tool for studying the distribution of Northern corn leaf blight and other foliar diseases, and identifying the pathogenic races moving through the province.
In 2015, eyespot showed a surprising surge in Ontario cornfields, along with Northern corn leaf blight. “Both diseases were found in almost all fields visited in southern and western Ontario, with 40 per cent of the affected fields having incidence levels of greater than or equal to 30 per cent and one-fourth of the fields having a severity of greater than or equal to five (greater than 20 per cent of the leaf area affected),” reads the report.
But Tenuta says eyespot doesn’t come as a shock to Ontario growers.
“We’ve always had eyespot. We’re just seeing more of it,” Tenuta says. “Many of these diseases are residue-borne, so as we leave more residue we’ll see more disease.”
What does this mean for growers? According to Tenuta, eyespot sometimes means a four to six bushels per acre yield loss, but in conjunction with other diseases, it can cause problematic stress on the plant.
“Where eyespot could be an issue would be on seed corn, where you have a relatively susceptible seed corn inbred,” he says. If the variety is susceptible to other foliar leaf diseases as well, these plants can’t tolerate as much stress, so the impact will be more substantial.
Variety, variety, variety
Management for eyespot comes down to variety.
“It doesn’t matter what disease we’re talking about – the first step is always effective resistant variety selection,” Tenuta says. “The most important decision a grower can make is which particular variety or hybrid they’ll select.”
If a field has a history of eyespot, growers should choose good-yielding varieties with decent resistance.
“The next thing is scouting to determine the amount of disease there: is it a threat? Is it down low in the canopy, or high up? If you’ve got eyespot, you have good conditions for other leaf diseases,” he says.
If disease reaches threshold levels, fungicide application is necessary.
When it comes to tillage, growers may have tough decisions to make when it comes to eyespot and other foliar leaf diseases, Tenuta says. Because eyespot relies on residues as a food source, removal of residues means the fungus can’t spread enough to trouble the next crop. “If they can’t feed, they can’t grow and they can’t infect,” he says.
But growers need to assess whether periodic tillage is right for their operations on a case-by-case basis. “It’s an effective tool, but you have to consider some of the other benefits of conservation tillage in terms of soil erosion. And just because we work the ground doesn’t mean the risk is eliminated – you might be reducing your in-field inoculum, but in many cases we have enough spores moving in from other fields,” he says.
As for the future? More eyespot resistant varieties may be on the way soon. Lana Reid, a research scientist at AAFC’s Ottawa Research and Development Centre, and her team are working on developing a number of inbreds with resistance to a variety of common foliar diseases, including CO450, a corn inbred line that is highly resistant to eyespot. It was made available to breeders in 2013.
“This survey, I would say, is of great value – it gives direction to the research and to breeding projects,” Jindal says.