Canola producers will want to monitor crop emergence closely for any signs of flea beetle damage.
The insect overwinters as an adult and wakes up hungry, with activity increasing as the temperature warms up.
Canola Council of Canada Agronomist Keith Gabert says the insects can cause a lot of damage in a short period of time, which is why scouting the crop on a regular basis is so important.
The key is to stay ahead of the insect by getting a good emergence and stand establishment with five to eight plants per square foot up and growing vigorously.
He says that's not always the case, so producers want to be scouting often enough to sort of catch any issues that might be arising.
Gabert says producers will want to watch for flea beetle feeding or damage like pit marks or pock marks showing up on the clover shaped cotyledons.
"Canola that's emerging from the ground can handle a fair bit of feeding 10 per cent damage actually looks quite striking or looks concerning. We do need to remember that the current round of seed treatments requires some feeding on the part of the flea beetle, so that gets into their stomach, gets ingested, and gives them a bit of a headache or kills them off at least slows them down enough to let that crop get ahead. We really want to get that canola growing through to about the four-leaf stage when any flea beetle feeding that might happen probably won't have an impact on it."
He says feeding damage can advance quickly from 10 per cent to the economic action threshold of 25 percent when producers might want to look at using a foliar insecticide.
"I tell growers to really watch because we can go from 25 per cent action threshold through to a 50 per cent economic damage threshold, where we expect to see some yield loss happening relatively quickly."
The following information on standing up to flea beetles was contributed by Keith Gabert.
When we asked canola farmers what the greatest economic risk to their canola production was, they ranked flea beetles #1*. Scenarios that require multiple in-season foliar sprays are often the result of a slow-establishing non-competitive crop. Strong stand establishment can help reduce flea beetle risk – here are tips to achieve this objective.
Target 5-8 plants per square foot
Canola crops that establish quickly and have five to eight plants per square foot usually face minimal risk from flea beetle feeding. A plant population at the high end of that range will mean more plants for a fixed number of flea beetles. That means fewer beetles per plant, a situation more likely to keep leaf area loss below the threshold of 25 per cent. The graphic below is a visual representation of this point.
Seed shallow into warm, moist soil
These soil conditions are ideal. A later seeding date may reduce the flea beetle risk if it means warmer soils and faster growth. Like most agronomy decisions, delayed seeding comes with tradeoffs: it may reduce flea beetle risk but may not be ideal to avoid summer heat on flowers and limit fall frost risk. If soils are dry, seeding down into moisture may allow for seed germination, but often results in poor emergence and an extended emergence period. With any delays, seed treatment protection may not last through the at-risk period.
Use safe rates of seed-placed fertilizer
The recommendation is to use only phosphorus in the seed row and no more than 20 lb./ac. of actual phosphate. Higher rates of seed-placed fertilizer add more stress, slow the pace of growth and reduce the stand.
Flea beetles will emerge from hibernation hungry and increase their activity once air temperatures reach 15°C. Regular scouting for flea beetle damage is essential and should be done until your crop is well established.
For more on flea beetle management tips, how to make the spray decision and how to improve foliar spray results, check out these Canola Watch articles available at canolawatch.org/fundamentals: Flea beetles: Management tips and The flea beetle spray decision: 8 steps. While there, please sign up to receive the weekly Canola Watch e-newsletter, answering the top canola agronomy questions from across the Prairies.
*Canola Council of Canada 2022 survey results