Soroka: Effects of Late Season Flea Beetle Feeding on Canola Seed Yields

Date: April 2009
Term: 5 years
Status: Completed
Researcher(s): Dr. Juliana Soroka, Agriculture and Agri-Food Canada, Saskatoon
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: ACPC, MCGA

Project Summary

The best defense against fall flea beetle damage to canola seed yields was to seed at mid-May or earlier. Seeding date had the greatest influence on harvest parameters for all factors investigated, and in most trials earlier seeded plots outyielded later seeded plots.

On occasion, numbers of flea beetles in the summer generation are high in many areas across the prairies. Extensive flea beetle feeding on maturing canola foliage, stems, and pods can occur in years with long, warm autumns. Producers anxious to maintain seed yields wish to know how much feeding maturing canola can tolerate before economic damage occurs. Until this study, there were no economic thresholds for flea beetle damage to canola late in the season.

The objectives of this project were to determine the impact of fall feeding by crucifer-feeding flea beetles on canola growth and seed yield, with the aim of developing an economic threshold for fall flea beetle feeding. The project also monitored flea beetle populations to determine the patterns of movement to and from crops, with the aim of developing methods of forecasting flea beetle populations in the spring.

All photos of flea beetle damage to seed pods – this occurred in cages and were a worst case scenario, and even so yield reduction occurred only on the least mature pods.

Larry Grenkow, AAFC Saskatoon Research Centre

Field trials were established during the 2004-2006 summer seasons to determine the effects of late-season flea beetle feeding on seed yields of canola at the Saskatoon Research Centre field site. However, the natural flea beetle population over most of the prairies crashed in the spring of 2004, resulting in few effects of flea beetle feeding on canola yields from 2004 to 2006. The project was extended through funding from the Pest Management Centre of AAFC to include the 2007 and 2008 summer seasons, during which time flea beetle numbers approached damaging levels.

In all studies in all years, seeding date had the greatest influence on harvest parameters of the three field trials investigated, and in most trials earlier seeded plots outyielded later seeded plots. When harvest results were combined over years, seeding dates, and cultivars, the application of insecticide to plots late in the season did not have any impact on canola seed yields or weights, indicating that significant flea beetle damage to canola prior to harvest is not a common occurrence. The results of this project show that the best defense against fall flea beetle damage to canola seed yields was to seed at mid-May or earlier.

For late season economic thresholds, the project found that flea beetle feeding that occurs when seeds in lower pods of canola are beyond the green stage is unlikely to affect seed yields. And even when seeds are still green, numbers higher than 100 flea beetles per plant, and for some cultivars higher than 350 per plant, may be necessary to cause significant yield reductions. An adjustment to these numbers may be necessary for conditions in which multiple pests such as flea beetles and diamondback moths are present concurrently in the field late in the season.

Monitoring of Flea Beetle Movement with Sticky Card Traps

Researchers conducted another experiment near Saskatoon using yellow sticky traps to try to forecast the presence of flea beetle populations before they entered canola fields in spring. They placed yellow sticky traps (125x75 mm, Phero Tec, Delta, BC) in fields to be seeded to canola and near canola stubble fields, to trap flea beetles from the beginning of April until late June and again after harvest in 2004-2006. Traps were placed at the edges of field headlands, grass verges, or shelterbelts, and then at distances into canola fields to determine the timing and direction of flea beetle invasion into the fields. Spring flea beetle numbers were very low, and few conclusions could be drawn from their analyses. Overall, the study found that the use of yellow sticky traps as a monitoring and predictive tool for flea beetle invasion into canola fields is not reliable, and many questions must be answered before it may or may not become a useful tool in flea beetle management.

Full Report PDF: Effects of Late Season Flea Beetle Feeding on Canola Seed Yields