Now’s the time to scout canola fields for flea beetles, says Derwyn Hammond, the Canola Council of Canada’s Manitoba agronomy specialist.
Fields thinned by frost May 27, or struggling because of the cool, dry spring, are especially vulnerable.
“In stands that have been thinned out that’s going to focus that flea beetle population on a smaller number of plants,” said Hammond, who’s based in Brandon. “It’s important guys stay on top of it because you can’t afford anymore losses of the plants. Again, be on the conservative side with the threshold when you pull the trigger for foliar (insecticide application).”
The canola council recommends spraying an insecticide to control flea beetles when 25 per cent of the canola plant’s leaf area is lost and the flea beetles are still active. Studies show yields don’t suffer until 50 per cent of the leaf is lost, but in moderate to heavy infestations a 25 per cent threshold gives the farmer a bit of time to spray before yields are compromised, Hammond said.
“There are some areas where flea beetles are pretty active,” he said. “It’s better to be scouting too soon than not soon enough.”
Hammond said he heard of one farmer in the Swan Lake area who re-seeded some canola in patches decimated by voracious flea beetles.
Seed treatments protect canola for two to four weeks after seeding, depending on the product, Hammond said. Protection has, or soon will, run out on early-seeded canola.
Frost throughout much of agro-Manitoba May 27 injured some canola fields, but Hammond said he expects most will recover, especially in areas where temperatures ranged from 0 to -2°C. However, there were some places — especially south of the Trans-Canada Highway where it was colder. According to Manitoba Agriculture, Food and Rural Initiatives’ website it was -4.1°C in Gretna.
Frost damage depends on how cold it got and for how long and also whether the canola was hardened off or not. Fields exposed to cooler temperatures are more frost-tolerant.
The canola council recommends waiting at least four days before assessing frost-damaged canola.
“Even with blackened cotyledons and/or leaves, re-growth can occur in four to 10 days,” the council said in a news release last week.
“Frost damage to seedlings in the spring has never been more than a minor problem across Western Canada,” the council says in a fact sheet on frost damage.
The main thing to consider is whether the growing point in the young plant is still alive.
“If there is any green colour at the centre of the leaf rosettes, the majority of plants should recover and yields will be higher than if the field is worked and re-seeded,” the council release said.
— Allan Dawson is a reporter for the Manitoba Co-operator.