Early scouting can help ensure canola crops make it through the first few weeks in good shape.
“With the wet conditions, many growers across the Prairies are struggling to get all their canola acres seeded. In the rush to finish seeding, they must remember to scout those fields that have already emerged,” says Troy Prosofsky, agronomy specialist with the Canola Council of Canada (CCC).
Young canola seedlings are especially vulnerable to cutworms, flea beetles and seedling diseases, particularly if they are struggling through cool temperatures or frost, damage from wind or hail, and this season’s challenge — excess moisture stress.
Flea beetle protection on early-seeded canola will be tapering off, and some growers have already applied a foliar insecticide this year. When 25% of the leaf area is damaged or missing, farmers should have their sprayers ready to go. The economic threshold is about 50% of leaf area missing or damaged, but flea beetle damage can move from 25% to 50% within hours if the insects are active and canola is growing more slowly than the rate of feeding.
Under warm calm conditions, fields should be scouted 4 to 5 times a week through the high-risk period. And while flea beetles do slow down in cool, wet weather, they may take refuge on stems and the undersides of leaves. Growers are advised to watch for stem feeding, which can be even more damaging.
Big bald patches? Could be cutworms
Growers are advised to dig down and check for cutworms where there are distinct patches — where plants are missing entirely, or where plants are drooping or appear cut off. Cutworm damage usually appears first on light textured soils, hilltops and south facing slopes where soil temperatures are warmer. To scout, growers can use a trowel dig in the top 2 inches of soil and sift to uncover cutworms. Cutworms prefer dry soil. If digging in moisture, cutworms tend to be close to the soil surface.
“If you do spot freshly severed seedlings, dig to make sure cutworms are the cause,” Prosofsky says. “The preferred time to spray is in the evening or at night and when the economic threshold of 3-4 cutworms per metre square is reached.”
Fast-emerging canola can outgrow seedling diseases
Canola seeded shallow into warm, moist soils will emerge quickly, growing through the seedling disease window while the seed treatment is still strong. Continue to watch for signs of disease while scouting for insects.
Seedling diseased caused by fusarium and pythium species tend to be worse in cool, wet conditions while rhizoctonia, tends to be worse when canola emergence is delayed due to cool, dry conditions.
“The broad spectrum fungicide seed treatments used to treat certified seed typically provide good protection from these seedling diseases,” says Derwyn Hammond, CCC senior agronomy specialist.
“The tell-tale sign of disease is patchy emergence up to the four-leaf stage of the crop. Seeds or seedlings may decay prior to emergence or the seedlings may emerge and appear normal, then stagnate at the two- to four-leaf stages. These plants eventually die,” Hammond says.
But some of these symptoms also point to cutworm damage. This is why close scouting early in the season is important. “At these early stages, dead plants will decay and disappear quickly, making it impossible to accurately identify the cause,” Hammond says. “Determining the exact cause of emergence issues will determine if control measures can be used. It is the first step in avoiding similar problems in the future.”
