At the start of spring, the cool, wet weather delayed emergence of flea beetles and the early to mid-May-seeded canola. Now, the hot weather has pushed flea beetles to emerge in large numbers just as the canola is popping. After the seed sits in the ground for 21+ days with little plant growth, the effectiveness and residue of the neonicotinoid seed treatment is significantly reduced. This week some growers are spraying a foliar ‘rescue’ insecticide treatment on top of the insecticide seed treatment to manage the ‘feeding frenzy’ of flea beetles. In some case, three foliar applications were applied to manage the different emergence waves of flea beetles. Hot spots are in the major canola producing areas of ND including North Central (Bottineau Co.), Northeast (Cavalier Co.) and Southwest.
Fields should be scouted daily to identify economic injury or poor performance of insecticide seed treatments. Look for pitting and defoliation on cotyledons and true leaves when scouting. Flea beetle often concentrate on edges of fields in cool wet weather. Walk a W pattern and scout five sites per field. Estimate defoliation on 10 plants per site. Calculate the average defoliation level among the plants inspected.
For foliar insecticide applications, the action threshold is when an average of 20-25% defoliation is found on the cotyledons and/or first true leaves, and beetles are actively feeding in the field.
Foliar treatments must be made quickly. The weakness of foliar control strategies is the inability to cover large number of acres quickly when feeding pressure is high, and residual protection by the insecticides is short (only 5-10 days depending on weather and rate of insecticide), allowing for reinfestation to occur.
Pyrethroid insecticides (a.i. bifenthrin, deltamethrin, gamma-cyhalothrin, zeta-cypermethrin) provide good control of flea beetles and a 7- 10 day residual at the high-labeled rate. If it is hot (above 85⁰F), pyrethroid insecticides break down faster and are not as efficacious at controlling insect pests. So, insecticide application may need to be applied early in the morning or in the evening when daytime temperatures are hot. Insecticides registered for flea beetle management in canola are listed in the 2019 North Dakota Field Crop Insect Management Guide E1143.
For more information, please consult the NDSU Extension fact sheet Integrated Pest Management of Flea Beetles in Canola E1234 (revised).
Janet J. Knodel Lesley Lubenow
Extension Entomologist Area Extension Specialist/Agronomy
NDSU Langdon Research Extension Center

Posted in: NCGA News.
Last Modified: June 6, 2019