Flea beetles defoliating canola in South Dakota

SDSU Extension
Farm Forum

This year flea beetle emergence is behind schedule, but so is a lot of the canola emergence. We are observing very large flea beetle populations on late-planted canola that is just emerging. As a result, much of this canola is being heavily defoliated and will likely require foliar insecticide management to prevent further defoliation and loss of the developing plants.

Profile and Behavior

Small black and yellow beetle feeding on the green leaf of a canola plant.

There are three species of flea beetles that commonly infest canola and feed on the leaves. They are the crucifer flea beetle, hop flea beetle, and striped flea beetle. The main concern with flea beetle feeding occurs early in the season when vegetation can be rapidly removed by these pests.

The use of insecticide seed treatments can greatly reduce flea beetle feeding early in the growing season. However, if emergence of canola was delayed due to the spring conditions it is possible that the seed treatment is no longer effective against the flea beetles.

Scouting and Management

The first thing to keep in mind when scouting fields for flea beetles is that their 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. 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 the populations are limited to the field edges, a perimeter insecticide application can effectively reduce the populations. 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.

Flea beetle.