Cool, wet conditions, as seen in much of Western Canada during the early part of the 2024 growing season, are favourable for ascochyta, also called mycosphaerella blight, in peas.
The first step in taking action is to make sure that an infection is caused by mycosphaerella and not a bacterial blight, for which fungicide is not effective, explains Dennis Lange, pulse and soybean specialist with Manitoba Agriculture, in this new Pulse School episode.
While ascochyta or mycosphaerella lesions first appear as small, purplish-black or brown flecks (as shown above), bacterial blight symptoms are typically brown and shiny, with a water-soaked, greasy, or translucent appearance.
Once mycosphaerella is confirmed, the decision whether to apply a fungicide, and when, then comes down to four main risk factors: the density of the crop canopy, leaf wetness and humidity, the weather forecast, and symptoms on pea plants.
In the video, filmed at the 2024 Manitoba Crop Diagnostic School last week, Lange demonstrates how to use a decision worksheet published by Manitoba Pulse & Soybean Growers to evaluate whether the threshold for a fungicide application is met.
If symptoms continue to spread upward, and wet conditions continue, a second fungicide application 10–14 days later using a different fungicide group could be warranted, notes Lange.
“This year, based on the weather conditions that we’re seeing, we’re more than likely going to see grower spraying twice this year,” he says. “It’s also really important when you’re looking at spraying twice that you’re looking at rotating some of the fungicide groups. So rather than just using Group 11, for which they’ve have found some resistance in other areas, you need to look at using different groups.”
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