Flea beetles were a major concern last spring in most areas of Western Canada. The combination of dry and cold weather slowed canola growth allowing the flea beetles to continue to feed on the canola plants. The two main species of flea beetles are: Striped and Crucifer. Striped flea beetles are the most common species that can be found in fields due to seed treatments being more effective on Crucifer flea beetles.
Figure 1. Crucifer flea beetle on left and Striped flea beetle on right. Photo credit: John Gavloski, Manitoba Agriculture, Food and Rural Development
Monitoring/Scouting.
Scouting for flea beetles occurs from plant emergence up to the 4 leaf stage. Adults overwinter under plant material on field margins therefore, the headlands of a field will most often have a higher flea beetle population. It is important to scout the whole field to give a better indication of damage. Areas of the field along treelines or depressions beside sloughs are other hot spots to scout.
Examine the cotyledons for shot-hole feeding and assess the percentage of damage (Figure 2). It is also important to examine the stem of the plant because under windy, cold, and damp conditions flea beetles will feed on the stem of the plant.
The economic threshold for a foliar insecticide application is 25% cotyledon leaf damage. Use a lower threshold under the following conditions: hot and dry, if stem feeding is present, if the plant has undergone any frost damage, or if plant stand is below 6 plants per square foot. If the newest leaves are growing fast and do not have any damage on them, then spraying is probably unnecessary.
Figure 2. Percent Damage caused by flea beetle feeding. Source: Canola Council of Canada.
Management options
Seeding into warm soil and establishing an optimal plant stand can provide a buffer for flea beetle damage. Insecticide seed treatments provide residual control of flea beetles for the first 14-35 days. Flea beetles must ingest the seed treatment by feeding on the plant for control therefore, if populations are very high the seed treatment will have limited control. As mentioned earlier seed treatments are far more effective on Crucifer flea beetles than Striped flea beetles. If damage if above the economic threshold of 25%, then apply a foliar insecticide.
Summary
Flea beetles are a pest that must be scouted early in canola and mustard and can cause significant yield loss and reduction in plant stands if not properly managed.
Brandon Smith, PAg
Field Scouting Manager
brandon@croprecords.com