Soroka: Occurrence and Damage Potential of Root Maggots in Canola

Date: July 1999
Term: 2 years
Status: Completed
Researcher(s): Julie Soroka and Owen Olfert, Agriculture and Agri-Food Canada, Saskatoon SK and Lloyd Dosdall, Alberta Environment Centre
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: ACPC, AAFC Matching Investment Initiative

Project Summary

Crucifer root maggots are an economic pest of canola production. However, the extent of root maggot injury to canola across the prairies was not known. In the mid-90s, field losses from root maggots in Polish canola had been recorded as high as 52%, with 20% yield reductions in Argentine canola. Researchers wanted to determine the degree of damage done by root maggots to canola and other crucifer species, and to determine the degree of resistance of canola in cultivars and lines. The study found that crucifer root maggots are ubiquitous and damage canola roots wherever canola is grown across the Canadian Prairies. Differences were found in maggot damage among crucifer species, with yellow mustard suffering comparatively less root damage from maggots than other crucifers. No one canola cultivar or line stood out above any other entry as being more resistant to maggot feeding.

Crucifer root maggots are an economic pest of canola production. However, the extent of root maggot injury to canola across the prairies was not known. In the mid-90s, field losses from root maggots in Polish canola (Brassica rapa) had been recorded as high as 52%, with 20% yield reductions in Argentine canola (Brassica napus).

The objectives of this study were to determine the degree of damage done by root maggots to canola in commercial fields across the prairies. Researchers also wanted to determine the degree of resistance of canola in cultivars and lines of canola and other species at various locations. A third objective was to determine the relationship between the visual ratings of root maggot injury and the eventual yield loss.

Canola roots were collected prior to harvest from fields across Manitoba, Saskatchewan and Alberta and were examined for presence and degree of root maggot injury in 1996 and 1997. The study found that crucifer root maggots damaged canola roots wherever canola was grown across the Canadian Prairies. The greatest amount of damage over the greatest area was found in Alberta, although localized areas with heavily damaged roots occurred in the other two provinces, chiefly along the northern edge of the grain belt. On a field scale, this study found that maggot infestation levels per field and degree of feeding injury were fairly similar between B. napus and B. rapa.

Regional, co-op, variety, breeding line and agronomy trials at the Saskatoon Research Centre farm and sites at Melfort and Scott were rated for their resistance to root maggots. In total, 340 entries of seven crucifer species were evaluated for root maggot damage in 29 trials. Patterns of damage within and among species were generally similar in the two years, but there was less damage to roots in 1997 than in 1996. Maggot damage at Scott was much less than at Saskatoon, which in turn was generally less than at Melfort.

Significant differences in maggot infestation and injury among cultivars and breeding lines were found in many trials, especially when feeding levels were low. However, no material tested appeared immune to maggot injury, with all crucifer species fed upon to varying degrees. In general, ranking of species from most to least fed upon by maggots followed the order: B. napus (Argentine canola) = B. rapa (Polish canola) = B. juncea (brown and oriental mustard) ≈ B. carinata (Ethiopian mustard) > > Sinapis alba (yellow mustard). In side-by-side trials, Eruca sativa roots suffered more maggot damage than did Crambe abyssinica roots. Although there were differences in maggot damage within individual species, for example within B. napus cultivars and breeding lines, no one cultivar or line stood out above any other entry as being more resistant to maggot feeding.

Cultivars of B. rapa and B. napus were grown in field cages and infested with known numbers of root maggots to determine how much injury plants can tolerate before yields decreased. In the cage trial, the number of larvae per root and root damage index in July increased with increased fly infestation rates in both years. This early damage to B. napus roots was usually confined to epidermal tunneling, whereas damage to B. rapa roots often included penetration into the root cortex. Results at harvest were less consistent because of the presence of a second generation of root maggots discovered in the cages in August.

Despite visually having the greatest root damage, B. napus plants also had the largest 1000 seed weights. In 1997, 1000 seed weights were similar among the different fly infestation rates. Seed yields were variable and not significantly different among infestation levels or damage indices in either year, indicating that damage levels were not severe enough to affect seed yields. In this study, visual ratings of root maggot injury did not correlate with yield loss.

Scientific Publications

Soroka, J.J., L.M. Dosdall, O.O. Olfert and E. Seidle. 2004. Root maggots (Diptera: Anthomyiidae) in prairie canola (Brassica napus and B. rapa L.): Spatial and temporal surveys of root damage and prediction of damage levels. Can. J. Plant Sci. 84: 1172-1182.

Full Report PDF: Occurrence and Damage Potential of Root Maggots in Canola