2025: Seed Treatments for Flea Beetle Control in Spring Canola

Table 1. Location, experiment and agronomic information.

Materials and Methods

The trials were conducted at the NDSU Campus Agronomy farm in Fargo, the Langdon REC in Langdon, and near Roseau, MN. See Table 1 for planting dates, trial design, seeding rates and other information.

The efficacy of various seed treatments was evaluated for controlling crucifer and striped flea beetles in spring canola. Dekalb DK401TL canola seed was treated prior to planting. Two neonicotinoid seed treatments, Helix Vibrance (thiamethoxam) and Prosper Evergol (clothianidin) were tested alone and in combination with three rates of either Lumiderm or Fortenza (cyantraniliprole). Prosper Evergol also was tested in combination with two rates of Buteo Start (flupyradifurone), and in combination with the commercial rates of Lumiderm and Buteo Start. Additionally, foliar applications of Brigade 2EC were used alone and in combination with insecticidal seed treatments. Treatments, rates and active ingredients are listed in Table 2. Seed for Treatments 1, 2 and 12 were treated with a custom fungicide mix that equated with the active ingredients and rates found in the fungicide portion of Helix Vibrance.

Sampling activities, dates and crop stages are given in Table 3. Plots were rated for flea beetle feeding injury using the 0-6 scale developed by Dr. Janet Knodel, with 0 = no feeding and 6 = dead plant. Within each plot, 10 randomly selected seedlings were rated. For analysis, the 10 ratings were averaged for a single rating value per plot. We attempted to rate feeding injury at 7, 10 and 14 days after emergence (DAE), but this was not possible at each location due to weather and other field research commitments. The Roseau trial experienced extremely uneven emergence, which delayed injury rating timing and made injury ratings difficult. Plant stand was measured by counting the number of live plants in three square feet at two locations within each plot, and calculating the number of plants per square foot.

Foliar applications of Brigade 2EC (bifenthrin) were made to Treatments 2, 5, 8, 11 and 12 at Fargo and Langdon immediately following the second injury and defoliation ratings (May 27 and June 17), respectively. At Roseau, the first injury and defoliation ratings could not be completed before the foliar insecticide application. Instead, foliar applications were conducted on May 28, three days prior to the first rating. The second Brigade 2EC application was made to Treatment 12 one week after the first at all locations. All foliar applications were made with a backpack CO₂ sprayer using TeeJet 80015 flat fan nozzles at 40 PSI and a spray volume of 20 GPA.

Plots were harvested at maturity by straight combining with research plot combines, except at Langdon, where they were swathed prior to harvest. Grain weight, percent moisture content, and test weight were collected via the onboard weigh systems on the plot combines used at each location. Yields were adjusted to 8.5% standard grain moisture. All data were analyzed using the GLM procedure in SAS version 9.4 statistical software. The Fisher’s LSD post-hoc test (P<0.05) was used to test for significance among treatment means when the main effect F-test was significant (P<0.05).

Table 2. Treatments, active ingredients and rates used in the trial.

¹Fortenza substituted for Lumiderm, product rate adjusted to match commercial Lumiderm active ingredient rate.

²Commercial Buteo Start rate when used in combination with a neonicotinoid.

Table 3. Sampling activities, sampling dates (DAE = days after emergence), and crop stages.

Results and Discussion

Flea beetle activity and seedling feeding was unusually light due to cold, dry conditions from mid-May through June. These conditions favored canola growth but not flea beetle feeding activity. Flea beetles are most active and destructive to canola seedlings when warm, dry conditions exist during the susceptible seedling stages from emergence through the 6-leaf stage.

At Fargo, flea beetle numbers were very low and no feeding activity was noted at the first rating date (7 DAE). At the second rating date (15 DAE), there were significant differences among treatments for flea beetle injury, but not for percent defoliation. Injury ratings were very low and injury was mainly on the cotyledons. Injury progressed by the third rating date (24 DAE), and although there were significant differences among treatments for injury and defoliation, the values were again low. In general, all treatments that received a foliar bifenthrin application had less feeding injury and less defoliation at 24 DAE compared to insecticidal seed treatments only. There were no significant differences among treatments for established plant stand and grain yield. Treatment means for Fargo are presented in Table 4.

At Langdon, there were no significant differences among treatments for feeding injury or defoliation for the first rating date at 3 DAE. Flea beetle activity had just begun in the trial. At the second rating date (11 DAE), there were pronounced and significant differences among treatments for feeding injury and defoliation. In general, Treatment 1, Treatments 3 and 6 (neonicotinoids only), Treatments 2 and 12 (bifenthrin only), Treatments 4 and 7 (neonicotinoids + cyantraniliprole), and Treatments 5 and 8 (neonicotinoids + cyantraniliprole + bifenthrin) had greater feeding injury and defoliation compared to Treatments 9, 10, 11 and 13, all of which contained flupyradifurone. The same trend was demonstrated at the third rating date (18 DAE), although treatments that received a foliar bifenthrin application showed some improvement. By 18 DAE, seedlings were at the 4-leaf stage and flea beetle pressure was winding down. The same trend was observed for grain yield, where treatments that included flupyradifurone had higher yields compared to neonicotinoids alone and in combination with cyantraniliprole. There were no significant differences among treatments for established plant stand at either the first or second sampling date (only the second plant stand results are presented). Treatment means for Langdon are presented in Table 5.

Roseau experienced very uneven emergence, which complicated the timing of ratings and foliar bifenthrin applications. There were no significant differences among treatments for established plant stand, although stands were thin due to soil crusting during emergence. Significant treatment differences were observed for both rating dates (11 and 16 DAE) for feeding injury and defoliation. The same trend among treatments that was observed at Langdon also was observed at Roseau. Despite this, there were no significant differences among treatments for grain yield. Treatment means for Roseau are presented in Table 6.