Root Maggots in Canola
Root maggots come from flies laying their small white eggs near the soil surface of canola plants. Maggots will hatch in 3-10 days depending on temperatures. Once the maggots hatch they will find the canola roots and start feeding on the roots immediately. They will eat the root hairs and create extensive burrows through the main tap root, either killing or stunting plant growth in the process. Maggots will feed on canola roots for approximately 3-4 weeks before they pupate in the soil. The most problematic areas for root maggot have been reported in central, western, and northwestern Alberta. But root maggots do occur within Saskatchewan and Manitoba as well.
Root Maggot Damage
In severe cases root maggot damage can cause wilting, stunting, reduced flowering, decreased branching, decreased seed weight, and lower yields. If root maggot burrows are severe enough plant lodging and death can also occur. Root maggot damage can range from light to severe depending on cultural measures and the year. Root maggots tend to be worse in cool and wet years.
Root Maggot Control
There are no insecticides registered for controlling root maggot. Cultural practices are currently the best practices for root maggot management in canola. Increased seeding rates will help with the control of root maggot. Root maggots tend to be worse in lower plant densities with plants that have larger roots. Having at least a one-year break between canola crops will also help to significantly manage root maggot populations in a canola crop.
How to Scout for Root Maggot Damage
You want to scout for root maggot damage between flowering and podding stages. Start off by walking into any area of the field and collect 10 random plants. Bring the plants back to your truck and knock the dirt off of the roots. Assess the roots and keep track of what percentage of roots have what severity of damage.
E.g., If 4/10 plants have light to severe damage. Then that area would be assessed as 40% moderate root maggot damage.
Repeat these steps in 2-3 locations for a field >160 acres and 4-5 locations in a field < 320 acres. You should assess your fields twice between flowering and podding to get more accurate results. Results will help to determine if root maggots were the cause of a potential yield loss at harvest.
Overall there are no main controls for root maggot. Best practices to manage root maggots are to have at least a one-year break between canola crops. Assessing root maggot damage severities in the field will also help to determine if root maggots were the cause of a slight yield loss.