Some growers in the Peace River region are noticing very high levels of root maggots. Root maggots are one pest that can get worse — and in some cases, much worse — in a field with continuous canola. An AAFC study has shown very clearly that with continuous canola, there is a statistically significant increase in crop damage by root maggots. Based on average canola prices, the yield losses quantified in the study were equivalent to $108-$140 per acre after only three years of continuous canola. There are no insecticides available to control root maggot in canola, but providing a one year break seems to make a significant reduction in root maggot losses, the study found.
Lloyd Dosdall, the lead entomologist on the study, says that disease probably played a role in yield losses, even with intense root maggot feeding. Root disease and root maggot tend to go together — either because root maggot feeding provides an entry point for disease, or because thin stands caused by seedling disease resulted in more intense root maggot feeding. This latter scenario is supported by Dosdall research from the mid-1990s, which found the greatest root maggot damage occurred in stands planted at half the recommended seeding rate. In this study, lower stand densities produced plants with larger basal stem diameters that were correlated with significant increases in root maggot damage.