Flea beetle adults are still causing trouble in canola this week. In one field we scouted, flea beetle populations were very large and were causing large amounts of defoliation on late-planted canola that was just emerging (Figure 1). It is important to continue monitoring fields, even if they have been treated for flea beetles to ensure that the populations have been successfully managed and defoliation isn’t occurring.
Although there are three species of flea beetle that will feed on canola, we have only been observing the striped flea beetle (Figure 2) and the crucifer flea beetle (Figure 3).
Once canola reaches the fourth leaf stage, the impact of defoliation on yield is reduced. In addition, rain reduces flea beetle feeding as they will hide during rain events.
It is important to remember that flea beetle populations tend to be much higher near field edges. For this reason, the entire field should be scouted to determine how far the infestation goes. In some cases, treatment of the field edge will be sufficient to reduce flea beetle populations.
To scout for flea beetle feeding, walk in a W pattern and evaluate at least five sites per field. At each site, evaluate the defoliation that is present on ten plants (50 plants per field). Weather conditions can influence flea beetle infestations and their populations tend to be more uniformly distributed during hot, calm days. If populations persist, additional treatments may be required to reduce the flea beetle populations. Treatment is recommended when an average of 20-25% of defoliation has occurred on the cotyledons or the first true leaves and flea beetles are still feeding in the field.
If early season management is necessary, foliar insecticides will provide the best reduction in flea beetle populations. Pyrethroid insecticides with the active ingredients of bifenthrin, deltamethrin, gamma-cyhalothrin or zeta-cypermethrin at the high labeled rates provide good management of flea beetles. Make sure to select an insecticide that is labeled for canola and flea beetles.